diff --git a/.rubocop.yml b/.rubocop.yml
index a5b30b0..b36dbf4 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,3 +1,5 @@
+inherit_from: .rubocop_todo.yml
+
 require:
   - rubocop-rake
   - rubocop-rspec
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
new file mode 100644
index 0000000..f9d5a9f
--- /dev/null
+++ b/.rubocop_todo.yml
@@ -0,0 +1,23 @@
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2023-01-12 10:00:10 UTC using RuboCop version 1.42.0.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
+
+# Offense count: 2
+# Configuration parameters: AllowedMethods, AllowedPatterns, IgnoredMethods, CountRepeatedAttributes.
+Metrics/AbcSize:
+  Max: 23
+
+# Offense count: 2
+# Configuration parameters: CountComments, CountAsOne, ExcludedMethods, AllowedMethods, AllowedPatterns, IgnoredMethods.
+Metrics/MethodLength:
+  Max: 16
+
+# Offense count: 4
+# Configuration parameters: AssignmentOnly.
+RSpec/InstanceVariable:
+  Exclude:
+    - 'spec/nostr/client_spec.rb'
diff --git a/README.md b/README.md
index d31c505..0bed75a 100644
--- a/README.md
+++ b/README.md
@@ -4,8 +4,8 @@
 [![Maintainability](https://api.codeclimate.com/v1/badges/c7633eb2c89eb95ee7f2/maintainability)](https://codeclimate.com/github/wilsonsilva/nostr/maintainability)
 [![Test Coverage](https://api.codeclimate.com/v1/badges/c7633eb2c89eb95ee7f2/test_coverage)](https://codeclimate.com/github/wilsonsilva/nostr/test_coverage)
 
-Nostr client. Please note that the API is likely to change as the gem is still in development and has not yet reached a
-stable release. Use with caution.
+Asynchronous Nostr client. Please note that the API is likely to change as the gem is still in development and
+has not yet reached a stable release. Use with caution.
 
 ## Installation
 
@@ -19,10 +19,171 @@ If bundler is not being used to manage dependencies, install the gem by executin
 
 ## Usage
 
+### Requiring the gem
+
+All examples below assume that the gem has been required.
+
 ```ruby
 require 'nostr'
 ```
 
+
+### Generating a keypair
+
+```ruby
+keygen  = Nostr::Keygen.new
+keypair = keygen.generate_keypair
+
+keypair.private_key
+keypair.public_key
+```
+
+### Generating a private key and a public key
+
+```ruby
+keygen  = Nostr::Keygen.new
+
+private_key = keygen.generate_private_key
+public_key  = keygen.extract_public_key(private_key)
+```
+
+### Connecting to a Relay
+
+Clients can connect to multiple Relays. In this version, a Client can only connect to a single Relay at a time.
+
+You may instantiate multiple Clients and multiple Relays.
+
+```ruby
+client = Nostr::Client.new
+relay = Nostr::Relay.new(url: 'wss://relay.damus.io', name: 'Damus')
+
+client.connect(relay)
+```
+
+### WebSocket events
+
+All communication between clients and relays happen in WebSockets.
+
+The `:connect` event is fired when a connection with a WebSocket is opened. You must call `Nostr::Client#connect` first.
+
+```ruby
+client.on :connect do
+  # all the code goes here
+end
+```
+
+The `:close` event is fired when a connection with a WebSocket has been closed because of an error.
+
+```ruby
+client.on :error do |error_message|
+  puts error_message
+end
+
+# > Network error: wss://rsslay.fiatjaf.com: Unable to verify the server certificate for 'rsslay.fiatjaf.com'
+```
+
+The `:message` event is fired whenwhen data is received through a WebSocket.
+
+```ruby
+client.on :message do |message|
+  puts message
+end
+
+# > Network error: wss://rsslay.fiatjaf.com: Unable to verify the server certificate for 'rsslay.fiatjaf.com'
+```
+
+The `:close` event is fired when a connection with a WebSocket is closed.
+
+```ruby
+client.on :close do |code, reason|
+  # you may attempt to reconnect
+
+  client.connect(relay)
+end
+```
+
+### Requesting for events / creating a subscription
+
+A client can request events and subscribe to new updates after it has established a connection with the Relay.
+
+You may use a `Nostr::Filter` instance with as many attributes as you wish:
+
+```ruby
+client.on :connect do
+  filter = Nostr::Filter.new(
+    ids: ['8535d5e2d7b9dc07567f676fbe70428133c9884857e1915f5b1cc6514c2fdff8'],
+    authors: ['ae00f88a885ce76afad5cbb2459ef0dcf0df0907adc6e4dac16e1bfbd7074577'],
+    kinds: [Nostr::EventKind::TEXT_NOTE],
+    e: ["f111593a72cc52a7f0978de5ecf29b4653d0cf539f1fa50d2168fc1dc8280e52"],
+    p: ["f1f9b0996d4ff1bf75e79e4cc8577c89eb633e68415c7faf74cf17a07bf80bd8"],
+    since: 1230981305,
+    until: 1292190341,
+    limit: 420,
+  )
+
+  subscription = client.subscribe('a_random_subscription_id', filter)
+end
+```
+
+With just a few:
+
+```ruby
+client.on :connect do
+  filter = Nostr::Filter.new(kinds: [Nostr::EventKind::TEXT_NOTE])
+  subscription = client.subscribe('a_random_subscription_id', filter)
+end
+```
+
+Or omit the filter:
+
+```ruby
+client.on :connect do
+  subscription = client.subscribe('a_random_subscription_id')
+end
+```
+
+Or even omit the subscription id:
+
+```ruby
+client.on :connect do
+  subscription = client.subscribe('a_random_subscription_id')
+end
+```
+
+### Stop previous subscriptions
+
+You can stop receiving messages from a subscription by calling `#unsubscribe`:
+
+```ruby
+client.unsubscribe('your_subscription_id')
+```
+
+### Publishing an event
+
+To publish an event you need a keypair.
+
+```ruby
+# Set up the private key
+private_key = 'a630b06e2f883378d0aa335b9adaf7734603e00433350b684fe53e184f08c58f'
+user = Nostr::User.new(private_key)
+
+# Create a signed event
+event = user.create_event(
+  created_at: 1667422587, # optional, defaults to the current time
+  kind: Nostr::EventKind::TEXT_NOTE,
+  tags: [], # optional, defaults to []
+  content: 'Your feedback is appreciated, now pay $8'
+)
+
+# Send it to the Relay
+client.publish(event)
+```
+
+## NIPS
+
+- [x] [NIP-01 - Client](https://github.com/nostr-protocol/nips/blob/master/01.md)
+- [ ] [NIP-01 - Relay](https://github.com/nostr-protocol/nips/blob/master/01.md)
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies.
diff --git a/lib/nostr.rb b/lib/nostr.rb
index 179b7dd..325464a 100644
--- a/lib/nostr.rb
+++ b/lib/nostr.rb
@@ -1,6 +1,17 @@
 # frozen_string_literal: true
 
 require_relative 'nostr/version'
+require_relative 'nostr/keygen'
+require_relative 'nostr/client_message_type'
+require_relative 'nostr/filter'
+require_relative 'nostr/subscription'
+require_relative 'nostr/relay'
+require_relative 'nostr/key_pair'
+require_relative 'nostr/event_kind'
+require_relative 'nostr/event_fragment'
+require_relative 'nostr/event'
+require_relative 'nostr/client'
+require_relative 'nostr/user'
 
 # Encapsulates all the gem's logic
 module Nostr
diff --git a/lib/nostr/client.rb b/lib/nostr/client.rb
new file mode 100644
index 0000000..99125eb
--- /dev/null
+++ b/lib/nostr/client.rb
@@ -0,0 +1,176 @@
+# frozen_string_literal: true
+
+require 'event_emitter'
+require 'faye/websocket'
+
+module Nostr
+  # Clients can talk with relays and can subscribe to any set of events using a subscription filters.
+  # The filter represents all the set of nostr events that a client is interested in.
+  #
+  # There is no sign-up or account creation for a client. Every time a client connects to a relay, it submits its
+  # subscription filters and the relay streams the "interested events" to the client as long as they are connected.
+  #
+  class Client
+    include EventEmitter
+
+    # Instantiates a new Client
+    #
+    # @api public
+    #
+    # @example Instantiating a client that logs all the events it sends and receives
+    #   client = Nostr::Client.new(debug: true)
+    #
+    def initialize
+      @subscriptions = {}
+
+      initialize_channels
+    end
+
+    # Connects to the Relay's websocket endpoint
+    #
+    # @api public
+    #
+    # @example Connecting to a relay
+    #   relay = Nostr::Relay.new(url: 'wss://relay.damus.io', name: 'Damus')
+    #   client.connect(relay)
+    #
+    # @param [Relay] relay The relay to connect to
+    #
+    # @return [void]
+    #
+    def connect(relay)
+      execute_within_an_em_thread do
+        client = Faye::WebSocket::Client.new(relay.url, [], { tls: { verify_peer: false } })
+        parent_to_child_channel.subscribe { |msg| client.send(msg) }
+
+        client.on :open do
+          child_to_parent_channel.push(type: :open)
+        end
+
+        client.on :message do |event|
+          child_to_parent_channel.push(type: :message, data: event.data)
+        end
+
+        client.on :error do |event|
+          child_to_parent_channel.push(type: :error, message: event.message)
+        end
+
+        client.on :close do |event|
+          child_to_parent_channel.push(type: :close, code: event.code, reason: event.reason)
+        end
+      end
+    end
+
+    # Subscribes to a set of events using a filter
+    #
+    # @api public
+    #
+    # @example Creating a subscription with no id and no filters
+    #   subscription = client.subscribe
+    #
+    # @example Creating a subscription with an ID
+    #   subscription = client.subscribe(subscription_id: 'my-subscription')
+    #
+    # @example Subscribing to all events created after a certain time
+    #   subscription = client.subscribe(filter: Nostr::Filter.new(since: 1230981305))
+    #
+    # @param subscription_id [String] The subscription id. A random string.
+    # @param filter [Filter] A set of attributes that represent the events that the client is interested in.
+    #
+    # @return [Subscription] The subscription object
+    #
+    def subscribe(subscription_id: SecureRandom.hex, filter: Filter.new)
+      subscriptions[subscription_id] = Subscription.new(id: subscription_id, filter:)
+      parent_to_child_channel.push([ClientMessageType::REQ, subscription_id, filter.to_h].to_json)
+      subscriptions[subscription_id]
+    end
+
+    # Stops a previous subscription
+    #
+    # @api public
+    #
+    # @example Stopping a subscription
+    #  client.unsubscribe(subscription.id)
+    #
+    # @example Stopping a subscription
+    #  client.unsubscribe('my-subscription')
+    #
+    # @param subscription_id [String] ID of a previously created subscription.
+    #
+    # @return [void]
+    #
+    def unsubscribe(subscription_id)
+      subscriptions.delete(subscription_id)
+      parent_to_child_channel.push([ClientMessageType::CLOSE, subscription_id].to_json)
+    end
+
+    # Sends an event to a Relay
+    #
+    # @api public
+    #
+    # @example Sending an event to a relay
+    #  client.publish(event)
+    #
+    # @param event [Event] The event to be sent to a Relay
+    #
+    # @return [void]
+    #
+    def publish(event)
+      parent_to_child_channel.push([ClientMessageType::EVENT, event.to_h].to_json)
+    end
+
+    private
+
+    # The subscriptions that the client has created
+    #
+    # @api private
+    #
+    # @return [Hash{String=>Subscription}>]
+    #
+    attr_reader :subscriptions
+
+    # The channel that the parent thread uses to send messages to the child thread
+    #
+    # @api private
+    #
+    # @return [EventMachine::Channel]
+    #
+    attr_reader :parent_to_child_channel
+
+    # The channel that the child thread uses to send messages to the parent thread
+    #
+    # @api private
+    #
+    # @return [EventMachine::Channel]
+    #
+    attr_reader :child_to_parent_channel
+
+    # Executes a block of code within the EventMachine thread
+    #
+    # @api private
+    #
+    # @return [Thread]
+    #
+    def execute_within_an_em_thread(&block)
+      Thread.new { EventMachine.run(block) }
+    end
+
+    # Creates the communication channels between threads
+    #
+    # @api private
+    #
+    # @return [void]
+    #
+    def initialize_channels
+      @parent_to_child_channel = EventMachine::Channel.new
+      @child_to_parent_channel = EventMachine::Channel.new
+
+      child_to_parent_channel.subscribe do |msg|
+        emit :connect                           if msg[:type] == :open
+        emit :message, msg[:data]               if msg[:type] == :message
+        emit :error,   msg[:message]            if msg[:type] == :error
+        emit :close,   msg[:code], msg[:reason] if msg[:type] == :close
+      end
+    end
+  end
+end
diff --git a/lib/nostr/client_message_type.rb b/lib/nostr/client_message_type.rb
new file mode 100644
index 0000000..c8a3ae4
--- /dev/null
+++ b/lib/nostr/client_message_type.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Clients can send 3 types of messages, which must be JSON arrays
+  module ClientMessageType
+    # @return [String] Used to publish events
+    EVENT = 'EVENT'
+
+    # @return [String] Used to request events and subscribe to new updates
+    REQ = 'REQ'
+
+    # @return [String] Used to stop previous subscriptions
+    CLOSE = 'CLOSE'
+  end
+end
diff --git a/lib/nostr/event.rb b/lib/nostr/event.rb
new file mode 100644
index 0000000..eb44fd6
--- /dev/null
+++ b/lib/nostr/event.rb
@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+module Nostr
+  # The only object type that exists in Nostr is an event. Events are immutable.
+  class Event < EventFragment
+    # 32-bytes sha256 of the the serialized event data.
+    # To obtain the event.id, we sha256 the serialized event. The serialization is done over the UTF-8 JSON-serialized
+    # string (with no white space or line breaks)
+    #
+    # @api public
+    #
+    # @example Getting the event id
+    #   event.id # => 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460'
+    #
+    # @return [String]
+    #
+    attr_reader :id
+
+    # 64-bytes signature of the sha256 hash of the serialized event data, which is
+    # the same as the "id" field
+    #
+    # @api public
+    #
+    # @example Getting the event signature
+    #   event.sig # => ''
+    #
+    # @return [String]
+    #
+    attr_reader :sig
+
+    # Instantiates a new Event
+    #
+    # @api public
+    #
+    # @example Instantiating a new event
+    #   Nostr::Event.new(
+    #    id: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+    #    pubkey: '48df4af6e240ac5f7c5de89bf5941b249880be0e87d03685b178ccb1a315f52e',
+    #    created_at: 1230981305,
+    #    kind: 1,
+    #    tags: [],
+    #    content: 'Your feedback is appreciated, now pay $8',
+    #    sig: '123ac2923b792ce730b3da34f16155470ab13c8f97f9c53eaeb334f1fb3a5dc9a7f643
+    #          937c6d6e9855477638f5655c5d89c9aa5501ea9b578a66aced4f1cd7b3'
+    # )
+    #
+    #
+    # @param id [String] 32-bytes sha256 of the the serialized event data.
+    # @param sig [String] 64-bytes signature of the sha256 hash of the serialized event data, which is
+    # the same as the "id" field
+    #
+    def initialize(id:, sig:, **kwargs)
+      super(**kwargs)
+
+      @id = id
+      @sig = sig
+    end
+
+    # Converts the event to a hash
+    #
+    # @api public
+    #
+    # @example Converting the event to a hash
+    #  event.to_h
+    #
+    # @return [Hash] The event as a hash.
+    #
+    def to_h
+      {
+        id:,
+        pubkey:,
+        created_at:,
+        kind:,
+        tags:,
+        content:,
+        sig:
+      }
+    end
+
+    # Compares two events. Returns true if all attributes are equal and false otherwise
+    #
+    # @api public
+    #
+    # @example
+    #  event1 == event2 # => true
+    #
+    # @return [Boolean] True if all attributes are equal and false otherwise
+    #
+    def ==(other)
+      to_h == other.to_h
+    end
+  end
+end
diff --git a/lib/nostr/event_fragment.rb b/lib/nostr/event_fragment.rb
new file mode 100644
index 0000000..b979778
--- /dev/null
+++ b/lib/nostr/event_fragment.rb
@@ -0,0 +1,111 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Part of an +Event+. A complete +Event+ must have an +id+ and a +sig+.
+  class EventFragment
+    # 32-bytes hex-encoded public key of the event creator
+    #
+    # @api public
+    #
+    # @example
+    #   event.pubkey # => '48df4af6e240ac5f7c5de89bf5941b249880be0e87d03685b178ccb1a315f52e'
+    #
+    # @return [String]
+    #
+    attr_reader :pubkey
+
+    # Date of the creation of the vent. A UNIX timestamp, in seconds
+    #
+    # @api public
+    #
+    # @example
+    #   event.created_at # => 1230981305
+    #
+    # @return [Integer]
+    #
+    attr_reader :created_at
+
+    # The kind of the event. An integer from 0 to 2
+    #
+    # @api public
+    #
+    # @example
+    #   event.kind # => 1
+    #
+    # @return [Integer]
+    #
+    attr_reader :kind
+
+    # An array of tags. Each tag is an array of strings
+    #
+    # @api public
+    #
+    # @example Tags referencing an event
+    #  event.tags #=> [["e", "event_id", "relay URL"]]
+    #
+    # @example Tags referencing a key
+    #  event.tags #=> [["p", "event_id", "relay URL"]]
+    #
+    # @return [Array<Array>]
+    #
+    attr_reader :tags
+
+    # An arbitrary string
+    #
+    # @api public
+    #
+    # @example
+    #  event.content # => 'Your feedback is appreciated, now pay $8'
+    #
+    # @return [String]
+    #
+    attr_reader :content
+
+    # Instantiates a new EventFragment
+    #
+    # @api public
+    #
+    # @example
+    #   Nostr::EventFragment.new(
+    #     pubkey: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+    #     created_at: 1230981305,
+    #     kind: 1,
+    #     tags: [['e', '189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408']],
+    #     content: 'Your feedback is appreciated, now pay $8'
+    #   )
+    #
+    # @param pubkey [String] 32-bytes hex-encoded public key of the event creator.
+    # @param created_at [Integer] Date of the creation of the vent. A UNIX timestamp, in seconds.
+    # @param kind [Integer] The kind of the event. An integer from 0 to 2.
+    # @param tags [Array<Array>] An array of tags. Each tag is an array of strings.
+    # @param content [String] Arbitrary string.
+    #
+    def initialize(pubkey:, kind:, content:, created_at: Time.now.to_i, tags: [])
+      @pubkey = pubkey
+      @created_at = created_at
+      @kind = kind
+      @tags = tags
+      @content = content
+    end
+
+    # Serializes the event fragment, to obtain a SHA256 hash of it
+    #
+    # @api public
+    #
+    # @example Converting the event to a hash
+    #   event_fragment.serialize
+    #
+    # @return [Array] The event fragment as an array.
+    #
+    def serialize
+      [
+        0,
+        pubkey,
+        created_at,
+        kind,
+        tags,
+        content
+      ]
+    end
+  end
+end
diff --git a/lib/nostr/event_kind.rb b/lib/nostr/event_kind.rb
new file mode 100644
index 0000000..3e25861
--- /dev/null
+++ b/lib/nostr/event_kind.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Defines the event kinds that can be emitted by clients.
+  module EventKind
+    # The content is set to a stringified JSON object +{name: <username>, about: <string>,
+    # picture: <url, string>}+ describing the user who created the event. A relay may delete past set_metadata
+    # events once it gets a new one for the same pubkey.
+    #
+    # @return [Integer]
+    #
+    SET_METADATA = 0
+
+    # The content is set to the text content of a note (anything the user wants to say).
+    # Non-plaintext notes should instead use kind 1000-10000 as described in NIP-16.
+    #
+    # @return [Integer]
+    #
+    TEXT_NOTE = 1
+
+    # The content is set to the URL (e.g., wss://somerelay.com) of a relay the event creator wants to
+    # recommend to its followers.
+    #
+    # @return [Integer]
+    #
+    RECOMMEND_SERVER = 2
+  end
+end
diff --git a/lib/nostr/filter.rb b/lib/nostr/filter.rb
new file mode 100644
index 0000000..68189eb
--- /dev/null
+++ b/lib/nostr/filter.rb
@@ -0,0 +1,172 @@
+# frozen_string_literal: true
+
+module Nostr
+  # A filter determines what events will be sent in a subscription.
+  class Filter
+    # A list of event ids or prefixes
+    #
+    # @api public
+    #
+    # @example
+    #   filter.ids # => ['c24881c305c5cfb7c1168be7e9b0e150', '35deb2612efdb9e13e8b0ca4fc162341']
+    #
+    # @return [Array<String>, nil]
+    #
+    attr_reader :ids
+
+    # A list of pubkeys or prefixes, the pubkey of an event must be one of these
+    #
+    # @api public
+    #
+    # @example
+    #   filter.authors # => ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+    #
+    # @return [Array<String>, nil]
+    #
+    attr_reader :authors
+
+    # A list of a kind numbers
+    #
+    # @api public
+    #
+    # @example
+    #   filter.kinds # => [0, 1, 2]
+    #
+    # @return [Array<Integer>, nil]
+    #
+    attr_reader :kinds
+
+    # A list of event ids that are referenced in an "e" tag
+    #
+    # @api public
+    #
+    # @example
+    #   filter.e # => ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2']
+    #
+    # @return [Array<String>, nil]
+    #
+    attr_reader :e
+
+    # A list of pubkeys that are referenced in a "p" tag
+    #
+    # @api public
+    #
+    # @example
+    #   filter.p # => ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+    #
+    # @return [Array<String>, nil]
+    #
+    attr_reader :p
+
+    # A timestamp, events must be newer than this to pass
+    #
+    # @api public
+    #
+    # @example
+    #   filter.since # => 1230981305
+    #
+    # @return [Integer, nil]
+    #
+    attr_reader :since
+
+    # A timestamp, events must be older than this to pass
+    #
+    # @api public
+    #
+    # @example
+    #   filter.until # => 1292190341
+    #
+    # @return [Integer, nil]
+    #
+    attr_reader :until
+
+    # Maximum number of events to be returned in the initial query
+    #
+    # @api public
+    #
+    # @example
+    #   filter.limit # => 420
+    #
+    # @return [Integer, nil]
+    #
+    attr_reader :limit
+
+    # Instantiates a new Filter
+    #
+    # @api public
+    #
+    # @example
+    #   Nostr::Filter.new(
+    #     ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+    #     authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+    #     kinds: [0, 1, 2],
+    #     since: 1230981305,
+    #     until: 1292190341,
+    #     e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+    #     p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+    #   )
+    #
+    # @param kwargs [Hash]
+    # @option kwargs [Array<String>, nil] ids A list of event ids or prefixes
+    # @option kwargs [Array<String>, nil] authors A list of pubkeys or prefixes, the pubkey of an event must be one
+    # of these
+    # @option kwargs [Array<Integer>, nil] kinds A list of a kind numbers
+    # @option kwargs [Array<String>, nil] e A list of event ids that are referenced in an "e" tag
+    # @option kwargs [Array<String, nil>] p A list of pubkeys that are referenced in a "p" tag
+    # @option kwargs [Integer, nil] since A timestamp, events must be newer than this to pass
+    # @option kwargs [Integer, nil] until A timestamp, events must be older than this to pass
+    # @option kwargs [Integer, nil] limit Maximum number of events to be returned in the initial query
+    #
+    def initialize(**kwargs)
+      @ids = kwargs[:ids]
+      @authors = kwargs[:authors]
+      @kinds = kwargs[:kinds]
+      @e = kwargs[:e]
+      @p = kwargs[:p]
+      @since = kwargs[:since]
+      @until = kwargs[:until]
+      @limit = kwargs[:limit]
+    end
+
+    # Converts the filter to a hash, removing all empty attributes
+    #
+    # @api public
+    #
+    # @example
+    #   filter.to_h # => {:ids=>["c24881c305c5cfb7c1168be7e9b0e150"],
+    #    :authors=>["000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7"],
+    #    :kinds=>[0, 1, 2],
+    #    :"#e"=>["7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2"],
+    #    :"#p"=>["000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7"],
+    #    :since=>1230981305,
+    #    :until=>1292190341}
+    #
+    # @return [Hash] The filter as a hash.
+    #
+    def to_h
+      {
+        ids:,
+        authors:,
+        kinds:,
+        '#e': e,
+        '#p': p,
+        since:,
+        until: self.until,
+        limit:
+      }.compact
+    end
+
+    # Compares two filters. Returns true if all attributes are equal and false otherwise
+    #
+    # @api public
+    #
+    # @example
+    #  filter == filter # => true
+    #
+    # @return [Boolean] True if all attributes are equal and false otherwise
+    #
+    def ==(other)
+      to_h == other.to_h
+    end
+  end
+end
diff --git a/lib/nostr/key_pair.rb b/lib/nostr/key_pair.rb
new file mode 100644
index 0000000..169ea48
--- /dev/null
+++ b/lib/nostr/key_pair.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module Nostr
+  # A pair of public and private keys
+  class KeyPair
+    # 32-bytes hex-encoded private key
+    #
+    # @api public
+    #
+    # @example
+    #   keypair.private_key # => '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900'
+    #
+    # @return [String]
+    #
+    attr_reader :private_key
+
+    # 32-bytes hex-encoded public key
+    #
+    # @api public
+    #
+    # @example
+    #   keypair.public_key # => '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558'
+    #
+    # @return [String]
+    #
+    attr_reader :public_key
+
+    # Instantiates a key pair
+    #
+    # @api public
+    #
+    # @example
+    #   keypair = Nostr::KeyPair.new(
+    #     private_key: '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900',
+    #     public_key: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+    #   )
+    #
+    # @param private_key [String] 32-bytes hex-encoded private key.
+    # @param public_key [String] 32-bytes hex-encoded public key.
+    #
+    def initialize(private_key:, public_key:)
+      @private_key = private_key
+      @public_key = public_key
+    end
+  end
+end
diff --git a/lib/nostr/keygen.rb b/lib/nostr/keygen.rb
new file mode 100644
index 0000000..ea5a3fc
--- /dev/null
+++ b/lib/nostr/keygen.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+require 'ecdsa'
+require 'securerandom'
+
+module Nostr
+  # Generates private keys, public keys and key pairs.
+  class Keygen
+    # Instantiates a new keygen
+    #
+    # @api public
+    #
+    # @example
+    #   keygen = Nostr::Keygen.new
+    #
+    def initialize
+      @group = ECDSA::Group::Secp256k1
+    end
+
+    # Generates a pair of private and public keys
+    #
+    # @api public
+    #
+    # @example
+    #   keypair = keygen.generate_keypair
+    #   keypair # #<Nostr::KeyPair:0x0000000107bd3550
+    #    @private_key="893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900",
+    #    @public_key="2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558">
+    #
+    # @return [KeyPair] An object containing a private key and a public key.
+    #
+    def generate_key_pair
+      private_key = generate_private_key
+      public_key  = extract_public_key(private_key)
+
+      KeyPair.new(private_key:, public_key:)
+    end
+
+    # Generates a private key
+    #
+    # @api public
+    #
+    # @example
+    #   private_key = keygen.generate_private_key
+    #   private_key # => '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900'
+    #
+    # @return [String] A 32-bytes hex-encoded private key.
+    #
+    def generate_private_key
+      (SecureRandom.random_number(group.order - 1) + 1).to_s(16)
+    end
+
+    # Extracts a public key from a private key
+    #
+    # @api public
+    #
+    # @example
+    #   private_key = keygen.generate_private_key
+    #   public_key = keygen.extract_public_key(private_key)
+    #   public_key # => '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558'
+    #
+    # @return [String] A 32-bytes hex-encoded public key.
+    #
+    def extract_public_key(private_key)
+      group.generator.multiply_by_scalar(private_key.to_i(16)).x.to_s(16)
+    end
+
+    private
+
+    # The elliptic curve group. Used to generate public and private keys
+    #
+    # @api private
+    #
+    # @return [ECDSA::Group]
+    #
+    attr_reader :group
+  end
+end
diff --git a/lib/nostr/relay.rb b/lib/nostr/relay.rb
new file mode 100644
index 0000000..106c438
--- /dev/null
+++ b/lib/nostr/relay.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Relays expose a websocket endpoint to which clients can connect.
+  class Relay
+    # The websocket URL of the relay
+    #
+    # @api public
+    #
+    # @example
+    #   relay.url # => 'wss://relay.damus.io'
+    #
+    # @return [String]
+    #
+    attr_reader :url
+
+    # The name of the relay
+    #
+    # @api public
+    #
+    # @example
+    #   relay.name # => 'Damus'
+    #
+    # @return [String]
+    #
+    attr_reader :name
+
+    # Instantiates a new Relay
+    #
+    # @api public
+    #
+    # @example
+    #   relay = Nostr::Relay.new(url: 'wss://relay.damus.io', name: 'Damus')
+    #
+    # @return [String] The websocket URL of the relay
+    # @return [String] The name of the relay
+    #
+    def initialize(url:, name:)
+      @url = url
+      @name = name
+    end
+  end
+end
diff --git a/lib/nostr/subscription.rb b/lib/nostr/subscription.rb
new file mode 100644
index 0000000..06b9091
--- /dev/null
+++ b/lib/nostr/subscription.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require 'securerandom'
+
+module Nostr
+  # A subscription the result of a request to receive events from a relay
+  class Subscription
+    # A random string that should be used to represent a subscription
+    #
+    # @api public
+    #
+    # @example
+    #   subscription.id # => 'c24881c305c5cfb7c1168be7e9b0e150'
+    #
+    # @return [String]
+    #
+    attr_reader :id
+
+    # An object that determines what events will be sent in the subscription
+    #
+    # @api public
+    #
+    # @example
+    #   subscription.filter # => #<Nostr::Subscription:0x0000000110eea460 @filter=#<Nostr::Filter:0x0000000110c24de8>,
+    #   @id="0dd7f3fa06cd5f797438dd0b7477f3c7">
+    #
+    # @return [Filter]
+    #
+    attr_reader :filter
+
+    # Initializes a subscription
+    #
+    # @api public
+    #
+    # @example Creating a subscription with no id and no filters
+    #   subscription = Nostr::Subscription.new
+    #
+    # @example Creating a subscription with an ID
+    #   subscription = Nostr::Subscription.new(id: 'c24881c305c5cfb7c1168be7e9b0e150')
+    #
+    # @example Subscribing to all events created after a certain time
+    #   subscription = Nostr::Subscription.new(filter: Nostr::Filter.new(since: 1230981305))
+    #
+    # @param id [String] A random string that should be used to represent a subscription
+    # @param filter [Filter] An object that determines what events will be sent in that subscription
+    #
+    def initialize(filter:, id: SecureRandom.hex)
+      @id = id
+      @filter = filter
+    end
+
+    # Compares two subscriptions. Returns true if all attributes are equal and false otherwise
+    #
+    # @api public
+    #
+    # @example
+    #  subscription1 == subscription1 # => true
+    #
+    # @return [Boolean] True if all attributes are equal and false otherwise
+    #
+    def ==(other)
+      id == other.id && filter == other.filter
+    end
+  end
+end
diff --git a/lib/nostr/user.rb b/lib/nostr/user.rb
new file mode 100644
index 0000000..a14d425
--- /dev/null
+++ b/lib/nostr/user.rb
@@ -0,0 +1,92 @@
+# frozen_string_literal: true
+
+require 'schnorr'
+require 'json'
+
+module Nostr
+  # Each user has a keypair. Signatures, public key, and encodings are done according to the
+  # Schnorr signatures standard for the curve secp256k1.
+  class User
+    # A pair of private and public keys
+    #
+    # @api public
+    #
+    # @example
+    #   user.keypair # #<Nostr::KeyPair:0x0000000107bd3550
+    #    @private_key="893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900",
+    #    @public_key="2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558">
+    #
+    # @return [KeyPair]
+    #
+    attr_reader :keypair
+
+    # Instantiates a user
+    #
+    # @api public
+    #
+    # @example Creating a user with no keypair
+    #   user = Nostr::User.new
+    #
+    # @example Creating a user with a keypair
+    #   user = Nostr::User.new(keypair: keypair)
+    #
+    # @param keypair [Keypair] A pair of private and public keys
+    # @param keygen [Keygen] A private key and public key generator
+    #
+    def initialize(keypair: nil, keygen: Keygen.new)
+      @keypair = keypair || keygen.generate_key_pair
+    end
+
+    # Builds an Event
+    #
+    # @api public
+    #
+    # @example Creating a note event
+    #   event = user.create_event(
+    #     kind: Nostr::EventKind::TEXT_NOTE,
+    #     content: 'Your feedback is appreciated, now pay $8'
+    #   )
+    #
+    # @param event_attributes [Hash]
+    # @option event_attributes [String] :pubkey 32-bytes hex-encoded public key of the event creator.
+    # @option event_attributes [Integer] :created_at Date of the creation of the vent. A UNIX timestamp, in seconds.
+    # @option event_attributes [Integer] :kind The kind of the event. An integer from 0 to 2.
+    # @option event_attributes [Array<Array>] :tags  An array of tags. Each tag is an array of strings.
+    # @option event_attributes [String] :content Arbitrary string.
+    #
+    # @return [Event]
+    #
+    def create_event(event_attributes)
+      event_fragment = EventFragment.new(**event_attributes.merge(pubkey: keypair.public_key))
+      event_sha256 = Digest::SHA256.hexdigest(JSON.dump(event_fragment.serialize))
+
+      signature = sign(event_sha256)
+
+      Event.new(
+        id: event_sha256,
+        pubkey: event_fragment.pubkey,
+        created_at: event_fragment.created_at,
+        kind: event_fragment.kind,
+        tags: event_fragment.tags,
+        content: event_fragment.content,
+        sig: signature
+      )
+    end
+
+    private
+
+    # Signs an event with the user's private key
+    #
+    # @api private
+    #
+    # @param event_sha256 [String] The SHA256 hash of the event.
+    #
+    # @return [String] The signature of the event.
+    #
+    def sign(event_sha256)
+      hex_private_key = Array(keypair.private_key).pack('H*')
+      hex_message = Array(event_sha256).pack('H*')
+      Schnorr.sign(hex_message, hex_private_key).encode.unpack1('H*')
+    end
+  end
+end
diff --git a/lib/nostr/version.rb b/lib/nostr/version.rb
index 32cfe8d..70f6991 100644
--- a/lib/nostr/version.rb
+++ b/lib/nostr/version.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
 module Nostr
+  # The version of the gem
   VERSION = '0.1.0'
 end
diff --git a/nostr.gemspec b/nostr.gemspec
index 979fbdb..403f2fa 100644
--- a/nostr.gemspec
+++ b/nostr.gemspec
@@ -31,6 +31,13 @@ Gem::Specification.new do |spec|
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
+  spec.add_dependency 'bech32', '~> 1.3'
+  spec.add_dependency 'bip-schnorr', '~> 0.4'
+  spec.add_dependency 'ecdsa', '~> 1.2'
+  spec.add_dependency 'event_emitter', '~> 0.2'
+  spec.add_dependency 'faye-websocket', '~> 0.11'
+  spec.add_dependency 'json', '~> 2.6'
+
   spec.add_development_dependency 'bundler-audit', '~> 0.9'
   spec.add_development_dependency 'dotenv', '~> 2.8'
   spec.add_development_dependency 'guard', '~> 2.18'
@@ -40,6 +47,8 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'guard-rubocop', '~> 1.5'
   spec.add_development_dependency 'overcommit', '~> 0.59'
   spec.add_development_dependency 'pry', '~> 0.14'
+  spec.add_development_dependency 'puma', '~> 5.6'
+  spec.add_development_dependency 'rack', '~> 3.0'
   spec.add_development_dependency 'rake', '~> 13.0'
   spec.add_development_dependency 'rspec', '~> 3.12'
   spec.add_development_dependency 'rubocop', '~> 1.42'
diff --git a/spec/nostr/client_message_type_spec.rb b/spec/nostr/client_message_type_spec.rb
new file mode 100644
index 0000000..ed455a4
--- /dev/null
+++ b/spec/nostr/client_message_type_spec.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::ClientMessageType do
+  describe '::EVENT' do
+    it 'is a string' do
+      expect(described_class::EVENT).to eq('EVENT')
+    end
+  end
+
+  describe '::REQ' do
+    it 'is a string' do
+      expect(described_class::REQ).to eq('REQ')
+    end
+  end
+
+  describe '::CLOSE' do
+    it 'is a string' do
+      expect(described_class::CLOSE).to eq('CLOSE')
+    end
+  end
+end
diff --git a/spec/nostr/client_spec.rb b/spec/nostr/client_spec.rb
new file mode 100644
index 0000000..7943597
--- /dev/null
+++ b/spec/nostr/client_spec.rb
@@ -0,0 +1,309 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+# This test suite does not use let blocks because they don't work with EventMachine.
+#
+# EventMachine is a pain to work with, hence the use of sleep statements and instance variables.
+# I'll come back to fix this once I'm more familiar with it.
+
+RSpec.describe Nostr::Client do
+  def server(port)
+    @echo_server = EchoServer.new
+    @echo_server.listen(port)
+  end
+
+  def stop
+    @echo_server.stop
+  end
+
+  let(:client) { described_class.new }
+  let(:relay)  { Nostr::Relay.new(url: plain_text_url, name: 'localhost') }
+
+  let(:port)           { 4180 }
+  let(:plain_text_url) { "ws://0.0.0.0:#{port}/" }
+
+  before { server port }
+  after  { stop }
+
+  describe '.new' do
+    it 'creates an instance of a relay' do
+      client = described_class.new
+
+      expect(client).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#connect' do
+    it 'connects to the relay' do
+      connected = false
+
+      client.on :connect do
+        connected = true
+      end
+
+      client.connect(relay)
+      sleep 0.02
+
+      expect(connected).to be(true)
+    end
+  end
+
+  describe '#on' do
+    context 'when the connection is opened' do
+      it 'fires the :connect event' do
+        connect_event_fired = false
+
+        client.on :connect do
+          connect_event_fired = true
+        end
+
+        client.connect(relay)
+        sleep 0.02
+
+        expect(connect_event_fired).to be(true)
+      end
+    end
+
+    context 'when the client receives a message' do
+      it 'fires the :message event' do
+        received_message = nil
+
+        client.on :message do |_message|
+          received_message = 'hello'
+        end
+
+        client.connect(relay)
+
+        sleep 0.1
+
+        @echo_server.send('hello')
+
+        sleep 0.1
+
+        expect(received_message).to eq('hello')
+      end
+    end
+
+    context "when there's a connection error" do
+      it 'fires the :error event' do
+        connection_error_event = nil
+
+        client.on :error do |event|
+          connection_error_event = event
+        end
+
+        relay = Nostr::Relay.new(url: 'musk', name: 'localhost')
+
+        client.connect(relay)
+
+        sleep 0.1
+
+        expect(connection_error_event).to eq('Network error: musk: musk is not a valid WebSocket URL')
+      end
+    end
+
+    context 'when the connection is closed' do
+      it 'fires the :close event' do
+        connection_closed_code = nil
+        connection_closed_reason = nil
+
+        client.on :close do |code, reason|
+          connection_closed_code = code
+          connection_closed_reason = reason
+        end
+
+        client.connect(relay)
+
+        sleep 0.1
+
+        @echo_server.close(1000, 'We are done')
+
+        sleep 0.1
+
+        aggregate_failures do
+          expect(connection_closed_code).to eq(1000)
+          expect(connection_closed_reason).to eq('We are done')
+        end
+      end
+    end
+  end
+
+  describe '#subscribe' do
+    context 'when given a subscription id' do
+      it 'sends a REQ message to the relay, asking for all events and returns a subscription with the same id' do
+        id = '16605b59b539f6e86762f28fb57db2fd'
+
+        client = described_class.new
+
+        sent_message = nil
+        subscription = nil
+
+        client.on :message do |message|
+          sent_message = message
+        end
+
+        client.on :connect do
+          subscription = client.subscribe(subscription_id: id)
+        end
+
+        relay = Nostr::Relay.new(url: plain_text_url, name: 'localhost')
+        client.connect(relay)
+
+        sleep 0.01
+
+        aggregate_failures do
+          expect(sent_message).to eq('["REQ","16605b59b539f6e86762f28fb57db2fd",{}]')
+          expect(subscription).to eq(Nostr::Subscription.new(id:, filter: nil))
+        end
+      end
+    end
+
+    context 'when given a filter' do
+      it 'sends a REQ message to the relay, asking for filtered events and returns a subscription with same filter' do
+        allow(SecureRandom).to receive(:hex).and_return('16605b59b539f6e86762f28fb57db2fd')
+        filter = Nostr::Filter.new(since: 1_230_981_305)
+
+        client = described_class.new
+
+        sent_message = nil
+        subscription = nil
+
+        client.on :message do |message|
+          sent_message = message
+        end
+
+        client.on :connect do
+          subscription = client.subscribe(filter:)
+        end
+
+        relay = Nostr::Relay.new(url: plain_text_url, name: 'localhost')
+        client.connect(relay)
+
+        sleep 0.01
+
+        aggregate_failures do
+          expect(sent_message).to eq('["REQ","16605b59b539f6e86762f28fb57db2fd",{"since":1230981305}]')
+          expect(subscription).to eq(Nostr::Subscription.new(id: '16605b59b539f6e86762f28fb57db2fd', filter:))
+        end
+      end
+    end
+
+    context 'when given a subscription id and a filter' do
+      it 'sends a REQ message to the relay, asking for filtered events and returns a subscription with the same id' do
+        id = '16605b59b539f6e86762f28fb57db2fd'
+        filter = Nostr::Filter.new(since: 1_230_981_305)
+
+        client = described_class.new
+
+        sent_message = nil
+        subscription = nil
+
+        client.on :message do |message|
+          sent_message = message
+        end
+
+        client.on :connect do
+          subscription = client.subscribe(subscription_id: id, filter:)
+        end
+
+        relay = Nostr::Relay.new(url: plain_text_url, name: 'localhost')
+        client.connect(relay)
+
+        sleep 0.01
+
+        aggregate_failures do
+          expect(sent_message).to eq('["REQ","16605b59b539f6e86762f28fb57db2fd",{"since":1230981305}]')
+          expect(subscription).to eq(Nostr::Subscription.new(id:, filter:))
+        end
+      end
+    end
+
+    context 'when not given a subscription id nor a filter' do
+      it 'sends a REQ message to the relay, asking for all events and returns a subscription with a random id' do
+        allow(SecureRandom).to receive(:hex).and_return('16605b59b539f6e86762f28fb57db2fd')
+
+        client = described_class.new
+
+        sent_message = nil
+        subscription = nil
+
+        client.on :message do |message|
+          sent_message = message
+        end
+
+        client.on :connect do
+          subscription = client.subscribe
+        end
+
+        relay = Nostr::Relay.new(url: plain_text_url, name: 'localhost')
+        client.connect(relay)
+
+        sleep 0.01
+
+        aggregate_failures do
+          expect(sent_message).to eq('["REQ","16605b59b539f6e86762f28fb57db2fd",{}]')
+          expect(subscription).to eq(Nostr::Subscription.new(id: '16605b59b539f6e86762f28fb57db2fd', filter: nil))
+        end
+      end
+    end
+  end
+
+  describe '#unsubscribe' do
+    it 'sends a CLOSE message to the relay, asking it to stop a subscription' do
+      subscription_id = '16605b59b539f6e86762f28fb57db2fd'
+
+      client = described_class.new
+
+      sent_message = nil
+
+      client.on :message do |message|
+        sent_message = message
+      end
+
+      client.on :connect do
+        client.unsubscribe(subscription_id:)
+      end
+
+      relay = Nostr::Relay.new(url: plain_text_url, name: 'localhost')
+      client.connect(relay)
+
+      sleep 0.01
+
+      expect(sent_message).to eq(['CLOSE', { subscription_id: }].to_json)
+    end
+  end
+
+  describe '#publish' do
+    it 'sends a message to the relay' do
+      relay = Nostr::Relay.new(url: plain_text_url, name: 'localhost')
+      client = described_class.new
+      event = Nostr::Event.new(
+        id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+        pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+        created_at: 1_230_981_305,
+        kind: 1,
+        tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+        content: 'Your feedback is appreciated, now pay $8',
+        sig: '970fea8d213da86c583804522c45d04e61c18c433704b62f793f187bca82091c' \
+             '3884d6207c6511c0966ecf6230082179a49257b03e5a4d2d08da9124a190f1bb'
+      )
+
+      received_message = nil
+
+      client.on :message do |message|
+        received_message = message
+      end
+
+      client.on :connect do
+        client.publish(event)
+      end
+
+      client.connect(relay)
+
+      sleep 0.01
+
+      expect(received_message).to eq(['EVENT', event.to_h].to_json)
+    end
+  end
+end
diff --git a/spec/nostr/event_fragment_spec.rb b/spec/nostr/event_fragment_spec.rb
new file mode 100644
index 0000000..8f8b272
--- /dev/null
+++ b/spec/nostr/event_fragment_spec.rb
@@ -0,0 +1,90 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::EventFragment do
+  let(:event_fragment) do
+    described_class.new(
+      pubkey: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+      created_at: 1_230_981_305,
+      kind: 1,
+      tags: [
+        %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+        %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+      ],
+      content: 'Your feedback is appreciated, now pay $8'
+    )
+  end
+
+  describe '.new' do
+    it 'creates an instance of an event fragment' do
+      event_fragment = described_class.new(
+        pubkey: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+        created_at: 1_230_981_305,
+        kind: 1,
+        tags: [
+          %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+          %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+        ],
+        content: 'Your feedback is appreciated, now pay $8'
+      )
+
+      expect(event_fragment).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#content' do
+    it 'exposes the event fragment content' do
+      expect(event_fragment.content).to eq('Your feedback is appreciated, now pay $8')
+    end
+  end
+
+  describe '#created_at' do
+    it 'exposes the event fragment creation date' do
+      expect(event_fragment.created_at).to eq(1_230_981_305)
+    end
+  end
+
+  describe '#kind' do
+    it 'exposes the event fragment kind' do
+      expect(event_fragment.kind).to eq(1)
+    end
+  end
+
+  describe '#pubkey' do
+    it 'exposes the event fragment pubkey' do
+      expect(event_fragment.pubkey).to eq('ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460')
+    end
+  end
+
+  describe '#serialize' do
+    it 'serializes the event fragment according to NIP-01' do
+      serialized_event_fragment = event_fragment.serialize
+
+      expect(serialized_event_fragment).to eq(
+        [
+          0,
+          'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+          1_230_981_305,
+          1,
+          [
+            %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+            %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+          ],
+          'Your feedback is appreciated, now pay $8'
+        ]
+      )
+    end
+  end
+
+  describe '#tags' do
+    it 'exposes the event fragment tags' do
+      expect(event_fragment.tags).to eq(
+        [
+          %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+          %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+        ]
+      )
+    end
+  end
+end
diff --git a/spec/nostr/event_kind_spec.rb b/spec/nostr/event_kind_spec.rb
new file mode 100644
index 0000000..d83f36c
--- /dev/null
+++ b/spec/nostr/event_kind_spec.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::EventKind do
+  describe '::SET_METADATA' do
+    it 'is an integer' do
+      expect(described_class::SET_METADATA).to eq(0)
+    end
+  end
+
+  describe '::TEXT_NOTE' do
+    it 'is an integer' do
+      expect(described_class::TEXT_NOTE).to eq(1)
+    end
+  end
+
+  describe '::RECOMMEND_SERVER' do
+    it 'is an integer' do
+      expect(described_class::RECOMMEND_SERVER).to eq(2)
+    end
+  end
+end
diff --git a/spec/nostr/event_spec.rb b/spec/nostr/event_spec.rb
new file mode 100644
index 0000000..62f0980
--- /dev/null
+++ b/spec/nostr/event_spec.rb
@@ -0,0 +1,185 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Event do
+  let(:event) do
+    described_class.new(
+      id: '20f31a9b2a0ced48a167add9732ccade1dca5e34b44316e37da4af33bc8946a9',
+      pubkey: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+      created_at: 1_230_981_305,
+      kind: 1,
+      tags: [
+        %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+        %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+      ],
+      content: 'Your feedback is appreciated, now pay $8',
+      sig: '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39' \
+           '63d0086171f842ffebf1f7790ce147b4811a15ef3f59c76ec1324b970cc57ffe'
+    )
+  end
+
+  describe '#==' do
+    context 'when both events have the same attributes' do
+      it 'returns true' do
+        event1 = described_class.new(
+          id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+          pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+          created_at: 1_230_981_305,
+          kind: 1,
+          tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+          content: 'Your feedback is appreciated, now pay $8',
+          sig: '970fea8d213da86c583804522c45d04e61c18c433704b62f793f187bca82091c' \
+               '3884d6207c6511c0966ecf6230082179a49257b03e5a4d2d08da9124a190f1bb'
+        )
+
+        event2 = described_class.new(
+          id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+          pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+          created_at: 1_230_981_305,
+          kind: 1,
+          tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+          content: 'Your feedback is appreciated, now pay $8',
+          sig: '970fea8d213da86c583804522c45d04e61c18c433704b62f793f187bca82091c' \
+               '3884d6207c6511c0966ecf6230082179a49257b03e5a4d2d08da9124a190f1bb'
+        )
+
+        expect(event1).to eq(event2)
+      end
+    end
+
+    context 'when both events have at least one different attribute' do
+      it 'returns false' do
+        event1 = described_class.new(
+          id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+          pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+          created_at: 1_230_981_305,
+          kind: 1,
+          tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+          content: 'Your feedback is appreciated, now pay $8',
+          sig: '970fea8d213da86c583804522c45d04e61c18c433704b62f793f187bca82091c' \
+               '3884d6207c6511c0966ecf6230082179a49257b03e5a4d2d08da9124a190f1bb'
+        )
+
+        event2 = described_class.new(
+          id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+          pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+          created_at: 1_230_981_305,
+          kind: 1,
+          tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+          content: 'Your feedback is appreciated, now pay $8',
+          sig: '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39' \
+               '63d0086171f842ffebf1f7790ce147b4811a15ef3f59c76ec1324b970cc57ffe'
+        )
+
+        expect(event1).not_to eq(event2)
+      end
+    end
+  end
+
+  describe '.new' do
+    it 'creates an instance of an event' do
+      event = described_class.new(
+        id: '20f31a9b2a0ced48a167add9732ccade1dca5e34b44316e37da4af33bc8946a9',
+        pubkey: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+        created_at: 1_230_981_305,
+        kind: 1,
+        tags: [
+          %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+          %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+        ],
+        content: 'Your feedback is appreciated, now pay $8',
+        sig: '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39' \
+             '63d0086171f842ffebf1f7790ce147b4811a15ef3f59c76ec1324b970cc57ffe'
+      )
+
+      expect(event).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#content' do
+    it 'exposes the event content' do
+      expect(event.content).to eq('Your feedback is appreciated, now pay $8')
+    end
+  end
+
+  describe '#created_at' do
+    it 'exposes the event creation date' do
+      expect(event.created_at).to eq(1_230_981_305)
+    end
+  end
+
+  describe '#kind' do
+    it 'exposes the event kind' do
+      expect(event.kind).to eq(1)
+    end
+  end
+
+  describe '#id' do
+    it 'exposes the event id' do
+      expect(event.id).to eq('20f31a9b2a0ced48a167add9732ccade1dca5e34b44316e37da4af33bc8946a9')
+    end
+  end
+
+  describe '#pubkey' do
+    it 'exposes the event pubkey' do
+      expect(event.pubkey).to eq('ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460')
+    end
+  end
+
+  describe '#serialize' do
+    it 'serializes the event according to NIP-01' do
+      serialized_event = event.serialize
+
+      expect(serialized_event).to eq(
+        [
+          0,
+          'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+          1_230_981_305,
+          1,
+          [
+            %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+            %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+          ],
+          'Your feedback is appreciated, now pay $8'
+        ]
+      )
+    end
+  end
+
+  describe '#sig' do
+    it 'exposes the event signature' do
+      expect(event.sig).to eq(
+        '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39' \
+        '63d0086171f842ffebf1f7790ce147b4811a15ef3f59c76ec1324b970cc57ffe'
+      )
+    end
+  end
+
+  describe '#tags' do
+    it 'exposes the event tags' do
+      expect(event.tags).to eq(
+        [
+          %w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+          %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]
+        ]
+      )
+    end
+  end
+
+  describe '#to_h' do
+    it 'converts the event to a hash' do
+      expect(event.to_h).to eq(
+        id: '20f31a9b2a0ced48a167add9732ccade1dca5e34b44316e37da4af33bc8946a9',
+        pubkey: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+        created_at: 1_230_981_305,
+        kind: 1,
+        tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408],
+               %w[p 472f440f29ef996e92a186b8d320ff180c855903882e59d50de1b8bd5669301e]],
+        content: 'Your feedback is appreciated, now pay $8',
+        sig: '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39' \
+             '63d0086171f842ffebf1f7790ce147b4811a15ef3f59c76ec1324b970cc57ffe'
+      )
+    end
+  end
+end
diff --git a/spec/nostr/filter_spec.rb b/spec/nostr/filter_spec.rb
new file mode 100644
index 0000000..8026d46
--- /dev/null
+++ b/spec/nostr/filter_spec.rb
@@ -0,0 +1,143 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Filter do
+  let(:filter) do
+    described_class.new(
+      ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+      authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+      kinds: [0, 1, 2],
+      since: 1_230_981_305,
+      until: 1_292_190_341,
+      e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+      p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+    )
+  end
+
+  describe '#==' do
+    context 'when both filters have the same attributes' do
+      it 'returns true' do
+        filter1 = described_class.new(
+          ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+          authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+          kinds: [0, 1, 2],
+          since: 1_230_981_305,
+          until: 1_292_190_341,
+          e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+          p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+        )
+
+        filter2 = described_class.new(
+          ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+          authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+          kinds: [0, 1, 2],
+          since: 1_230_981_305,
+          until: 1_292_190_341,
+          e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+          p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+        )
+
+        expect(filter1).to eq(filter2)
+      end
+    end
+
+    context 'when both filters have at least one different attribute' do
+      it 'returns false' do
+        filter1 = described_class.new(
+          ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+          authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+          kinds: [0, 1, 2],
+          since: 1_230_981_305,
+          until: 1_292_190_341,
+          e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+          p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+        )
+
+        filter2 = described_class.new(
+          ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+          authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+          kinds: [1],
+          since: 1_230_981_305,
+          until: 1_292_190_341,
+          e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+          p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+        )
+
+        expect(filter1).not_to eq(filter2)
+      end
+    end
+  end
+
+  describe '.new' do
+    it 'creates an instance of a filter' do
+      filter = described_class.new(
+        ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+        authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+        kinds: [0, 1, 2],
+        since: 1_230_981_305,
+        until: 1_292_190_341,
+        e: ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+        p: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7']
+      )
+
+      expect(filter).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#ids' do
+    it 'exposes the filter ids' do
+      expect(filter.ids).to eq(['c24881c305c5cfb7c1168be7e9b0e150'])
+    end
+  end
+
+  describe '#authors' do
+    it 'exposes the filter authors' do
+      expect(filter.authors).to eq(['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'])
+    end
+  end
+
+  describe '#kinds' do
+    it 'exposes the filter kinds' do
+      expect(filter.kinds).to eq([0, 1, 2])
+    end
+  end
+
+  describe '#since' do
+    it 'exposes the filter since' do
+      expect(filter.since).to eq(1_230_981_305)
+    end
+  end
+
+  describe '#until' do
+    it 'exposes the filter until' do
+      expect(filter.until).to eq(1_292_190_341)
+    end
+  end
+
+  describe '#e' do
+    it 'exposes the filter e' do
+      expect(filter.e).to eq(['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'])
+    end
+  end
+
+  describe '#p' do
+    it 'exposes the filter p' do
+      expect(filter.p).to eq(['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'])
+    end
+  end
+
+  describe '#to_h' do
+    it 'converts the filter to a hash' do
+      expect(filter.to_h).to eq(
+        ids: ['c24881c305c5cfb7c1168be7e9b0e150'],
+        authors: ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+        kinds: [0, 1, 2],
+        '#e': ['7bdb422f254194ae4bb86d354c0bd5a888fce233ffc77dceb3e844ceec1fcfb2'],
+        '#p': ['000000001c5c45196786e79f83d21fe801549fdc98e2c26f96dcef068a5dbcd7'],
+        since: 1_230_981_305,
+        until: 1_292_190_341
+      )
+    end
+  end
+end
diff --git a/spec/nostr/key_pair_spec.rb b/spec/nostr/key_pair_spec.rb
new file mode 100644
index 0000000..3c4cd91
--- /dev/null
+++ b/spec/nostr/key_pair_spec.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::KeyPair do
+  let(:keypair) do
+    described_class.new(
+      private_key: '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900',
+      public_key: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558'
+    )
+  end
+
+  describe '.new' do
+    it 'creates an instance of a key pair' do
+      keypair = described_class.new(
+        private_key: '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900',
+        public_key: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558'
+      )
+
+      expect(keypair).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#private_key' do
+    it 'exposes the private key' do
+      expect(keypair.private_key).to eq('893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900')
+    end
+  end
+
+  describe '#public_key' do
+    it 'exposes the public key' do
+      expect(keypair.public_key).to eq('2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558')
+    end
+  end
+end
diff --git a/spec/nostr/keygen_spec.rb b/spec/nostr/keygen_spec.rb
new file mode 100644
index 0000000..0bc01c8
--- /dev/null
+++ b/spec/nostr/keygen_spec.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Keygen do
+  let(:keygen) { described_class.new }
+
+  describe '.new' do
+    it 'creates an instance of a keygen' do
+      keygen = described_class.new
+
+      expect(keygen).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#generate_key_pair' do
+    it 'generates a private/public key pair' do
+      keypair = keygen.generate_key_pair
+
+      aggregate_failures do
+        expect(keypair.private_key).to match(/[a-f0-9]{64}/)
+        expect(keypair.public_key).to match(/[a-f0-9]{64}/)
+      end
+    end
+  end
+
+  describe '#generate_private_key' do
+    it 'generates a private key' do
+      private_key = keygen.generate_private_key
+
+      expect(private_key).to match(/[a-f0-9]{64}/)
+    end
+  end
+
+  describe '#extract_public_key' do
+    it 'extracts a public key from a private key' do
+      private_key = '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900'
+      public_key = keygen.extract_public_key(private_key)
+
+      expect(public_key).to eq('2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558')
+    end
+  end
+end
diff --git a/spec/nostr/relay_spec.rb b/spec/nostr/relay_spec.rb
new file mode 100644
index 0000000..7992cb6
--- /dev/null
+++ b/spec/nostr/relay_spec.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Relay do
+  let(:relay) do
+    described_class.new(url: 'wss://relay.damus.io', name: 'Damus')
+  end
+
+  describe '.new' do
+    it 'creates an instance of a relay' do
+      relay = described_class.new(url: 'wss://relay.damus.io', name: 'Damus')
+
+      expect(relay).to be_an_instance_of(described_class)
+    end
+  end
+
+  describe '#name' do
+    it 'exposes the relay name' do
+      expect(relay.name).to eq('Damus')
+    end
+  end
+
+  describe '#public_key' do
+    it 'exposes the relay URL' do
+      expect(relay.url).to eq('wss://relay.damus.io')
+    end
+  end
+end
diff --git a/spec/nostr/subscription_spec.rb b/spec/nostr/subscription_spec.rb
new file mode 100644
index 0000000..509d1b4
--- /dev/null
+++ b/spec/nostr/subscription_spec.rb
@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Subscription do
+  let(:filter) do
+    Nostr::Filter.new(since: 1_230_981_305)
+  end
+
+  let(:subscription) do
+    described_class.new(id: 'c24881c305c5cfb7c1168be7e9b0e150', filter:)
+  end
+
+  describe '#==' do
+    context 'when both subscriptions have the same attributes' do
+      it 'returns true' do
+        subscription1 = described_class.new(id: 'c24881c305c5cfb7c1168be7e9b0e150', filter:)
+        subscription2 = described_class.new(id: 'c24881c305c5cfb7c1168be7e9b0e150', filter:)
+
+        expect(subscription1).to eq(subscription2)
+      end
+    end
+
+    context 'when both subscriptions have a different id' do
+      it 'returns false' do
+        subscription1 = described_class.new(id: 'c24881c305c5cfb7c1168be7e9b0e150', filter:)
+        subscription2 = described_class.new(id: '16605b59b539f6e86762f28fb57db2fd', filter:)
+
+        expect(subscription1).not_to eq(subscription2)
+      end
+    end
+
+    context 'when both subscriptions have a different filter' do
+      let(:other_filter) do
+        Nostr::Filter.new(since: 1_230_981_305, until: 1_292_190_341)
+      end
+
+      it 'returns false' do
+        subscription1 = described_class.new(id: 'c24881c305c5cfb7c1168be7e9b0e150', filter:)
+        subscription2 = described_class.new(id: 'c24881c305c5cfb7c1168be7e9b0e150', filter: other_filter)
+
+        expect(subscription1).not_to eq(subscription2)
+      end
+    end
+  end
+
+  describe '.new' do
+    context 'when no id is provided' do
+      it 'creates an instance of a subscription using a randomly generated id' do
+        allow(SecureRandom).to receive(:hex).and_return('a_random_string')
+
+        subscription = described_class.new(filter:)
+
+        expect(subscription.id).to eq('a_random_string')
+      end
+    end
+
+    context 'when an id is provided' do
+      it 'creates an instance of a subscription using that ID' do
+        subscription = described_class.new(
+          id: 'c24881c305c5cfb7c1168be7e9b0e150',
+          filter:
+        )
+
+        expect(subscription.id).to eq('c24881c305c5cfb7c1168be7e9b0e150')
+      end
+    end
+  end
+
+  describe '#filter' do
+    it 'exposes the subscription filter' do
+      expect(subscription.filter).to eq(filter)
+    end
+  end
+
+  describe '#id' do
+    it 'exposes the subscription id' do
+      expect(subscription.id).to eq('c24881c305c5cfb7c1168be7e9b0e150')
+    end
+  end
+end
diff --git a/spec/nostr/user_spec.rb b/spec/nostr/user_spec.rb
new file mode 100644
index 0000000..0d8413f
--- /dev/null
+++ b/spec/nostr/user_spec.rb
@@ -0,0 +1,126 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::User do
+  let(:keypair) do
+    Nostr::KeyPair.new(
+      private_key: '893c4cc8088924796b41dc788f7e2f746734497010b1a9f005c1faad7074b900',
+      public_key: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558'
+    )
+  end
+
+  let(:user) do
+    described_class.new(keypair:)
+  end
+
+  describe '.new' do
+    context 'when no key pair is provided' do
+      let(:nostr_keygen) do
+        instance_double(Nostr::Keygen, generate_key_pair: keypair)
+      end
+
+      it 'creates an instance of a user with a new key pair' do
+        allow(Nostr::Keygen).to receive(:new).and_return(nostr_keygen)
+
+        user = described_class.new
+
+        aggregate_failures do
+          expect(user).to be_an_instance_of(described_class)
+          expect(user.keypair).to eq(keypair)
+        end
+      end
+    end
+
+    context 'when a key pair is provided' do
+      it 'creates an instance of a user using the provided key pair' do
+        user = described_class.new(keypair:)
+
+        expect(user.keypair).to eq(keypair)
+      end
+    end
+  end
+
+  describe '#keypair' do
+    it 'exposes the user key pair' do
+      expect(user.keypair).to eq(keypair)
+    end
+  end
+
+  describe '#create_event' do
+    context 'when created_at is missing' do
+      let(:now) { instance_double(Time, to_i: 1_230_981_305) }
+
+      before { allow(Time).to receive(:now).and_return(now) }
+
+      it 'builds and signs an event using the user key pair and the current time' do
+        event = user.create_event(
+          kind: Nostr::EventKind::TEXT_NOTE,
+          tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+          content: 'Your feedback is appreciated, now pay $8'
+        )
+
+        expect(event).to eq(
+          Nostr::Event.new(
+            id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+            pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+            created_at: 1_230_981_305,
+            kind: 1,
+            tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+            content: 'Your feedback is appreciated, now pay $8',
+            sig: '970fea8d213da86c583804522c45d04e61c18c433704b62f793f187bca82091c' \
+                 '3884d6207c6511c0966ecf6230082179a49257b03e5a4d2d08da9124a190f1bb'
+          )
+        )
+      end
+    end
+
+    context 'when tags is missing' do
+      it 'builds and signs an event using the user key pair and empty tags' do
+        event = user.create_event(
+          kind: Nostr::EventKind::TEXT_NOTE,
+          tags: [],
+          created_at: 1_230_981_305,
+          content: 'Your feedback is appreciated, now pay $8'
+        )
+
+        expect(event).to eq(
+          Nostr::Event.new(
+            id: 'ed35331e66dc166109d45daff39b8c1bf83d4c0c7a59a9a8a23b240dc126d526',
+            pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+            created_at: 1_230_981_305,
+            kind: 1,
+            tags: [],
+            content: 'Your feedback is appreciated, now pay $8',
+            sig: 'f5a2cdc29723c888df52afd6f8c6e260110f74ed23fee3edbf39fff4a9f1b9f1' \
+                 'c93284b02d4eba0481325bb5555624ddf969d5905b63f17191f9132a0ddd97b0'
+          )
+        )
+      end
+    end
+
+    context 'when all attributes are present' do
+      it 'builds and signs an event using the user key pair' do
+        event = user.create_event(
+          created_at: 1_230_981_305,
+          kind: Nostr::EventKind::TEXT_NOTE,
+          tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+          content: 'Your feedback is appreciated, now pay $8'
+        )
+
+        expect(event).to eq(
+          Nostr::Event.new(
+            id: '2a3184512d34077601e992ba3c3215354b21a8c76f85c2c7f66093481854e811',
+            pubkey: '2d7661527d573cc8e84f665fa971dd969ba51e2526df00c149ff8e40a58f9558',
+            created_at: 1_230_981_305,
+            kind: 1,
+            tags: [%w[e 189df012cfff8a075785b884bd702025f4a7a37710f581c4ac9d33e24b585408]],
+            content: 'Your feedback is appreciated, now pay $8',
+            sig: '970fea8d213da86c583804522c45d04e61c18c433704b62f793f187bca82091c' \
+                 '3884d6207c6511c0966ecf6230082179a49257b03e5a4d2d08da9124a190f1bb'
+          )
+        )
+      end
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 2c1fcfe..9f469ed 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -20,6 +20,8 @@ end
 
 require 'nostr'
 
+Dir["#{File.dirname(__FILE__)}/support/**/*.rb"].each { |f| require f }
+
 RSpec.configure do |config|
   # Enable flags like --only-failures and --next-failure
   config.example_status_persistence_file_path = '.rspec_status'
diff --git a/spec/support/echo_server.rb b/spec/support/echo_server.rb
new file mode 100644
index 0000000..c8224ca
--- /dev/null
+++ b/spec/support/echo_server.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'puma'
+require 'puma/binder'
+require 'puma/events'
+
+class EchoServer
+  def call(env)
+    @socket = Faye::WebSocket.new(env, ['echo'])
+
+    @socket.onmessage = lambda do |event|
+      @socket.send(event.data)
+    end
+
+    @socket.rack_response
+  end
+
+  def send(message)
+    @socket.send(message)
+  end
+
+  def close(code, reason)
+    @socket.close(code, reason)
+  end
+
+  def log(*args); end
+
+  def listen(port)
+    events = Puma::Events.new(StringIO.new, StringIO.new)
+    binder = Puma::Binder.new(events)
+    binder.parse(["tcp://0.0.0.0:#{port}"], self)
+    @server = Puma::Server.new(self, events)
+    @server.binder = binder
+    @server.run
+  end
+
+  def stop
+    case @server
+    when Puma::Server then @server.stop(true)
+    else @server.stop
+    end
+  end
+end