OpenAI Crystal Client

A comprehensive Crystal client for the OpenAI API, auto-generated from the official OpenAPI specification.

Features

• Full coverage of the OpenAI API (2480 types, 220 endpoints)
• Type-safe request and response objects with JSON serialization
• Server-Sent Events (SSE) streaming support for chat completions
• Multipart form data support for file uploads
• Comprehensive error handling with typed exceptions
• Provider extension system for OpenAI-compatible APIs (DeepSeek, Groq, etc.)
• Auto-generated from OpenAPI spec v2.3.0

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     openai:
       github: dsisnero/openai

2. Run shards install

Usage

Basic Setup

require "openai"

# Create a client with your API key
client = OpenAI::Client.new(api_key: ENV["OPENAI_API_KEY"])

# Or use a custom base URL (for Azure OpenAI, proxies, etc.)
client = OpenAI::Client.new(
  api_key: ENV["OPENAI_API_KEY"],
  base_url: "https://your-resource.openai.azure.com"
)

Chat Completions

# Using helper methods (recommended)
request = OpenAI::CreateChatCompletionRequest.new(model: "gpt-4o")
  .add_system_message("You are a helpful assistant")
  .add_user_message("Hello, how are you?")

response = client.create_chat_completion(request)
puts response.choices.first.message.content

Using ChatMessages Module

# Using the ChatMessages factory module
request = OpenAI::CreateChatCompletionRequest.new(
  model: "gpt-4o",
  messages: [
    OpenAI::ChatMessages.system("You are a helpful assistant"),
    OpenAI::ChatMessages.user("What is 2 + 2?"),
  ] of OpenAI::ChatCompletionRequestMessage
)

response = client.create_chat_completion(request)
puts response.choices.first.message.content

Parsing Messages from JSON

# Parse messages from JSON (useful for loading conversations)
json_messages = %([
  {"role": "system", "content": "You are a helpful assistant"},
  {"role": "user", "content": "Hi there!"}
])

request = OpenAI::CreateChatCompletionRequest.new(model: "gpt-4o")
  .add_messages_from_json(json_messages)

response = client.create_chat_completion(request)
puts response.choices.first.message.content

Streaming Chat Completions

request = OpenAI::CreateChatCompletionRequest.new(model: "gpt-4o")
  .add_user_message("Tell me a story")

request.stream = true

client.create_chat_completion_stream(request) do |chunk|
  chunk.choices.each do |choice|
    if content = choice.delta.content
      print content
    end
  end
end
puts

Embeddings

request = OpenAI::CreateEmbeddingRequest.new(
  model: "text-embedding-3-small",
  input: "The quick brown fox jumps over the lazy dog"
)

response = client.create_embedding(request)
embedding = response.data.first.embedding
puts "Embedding dimension: #{embedding.size}"

Image Generation

request = OpenAI::CreateImageRequest.new(
  model: "dall-e-3",
  prompt: "A white siamese cat",
  n: 1,
  size: OpenAI::CreateImageRequestSize::N1024X1024
)

response = client.create_image(request)
puts response.data.first.url

Error Handling

begin
  response = client.create_chat_completion(request)
rescue ex : OpenAI::AuthenticationError
  puts "Invalid API key: #{ex.message}"
rescue ex : OpenAI::RateLimitError
  puts "Rate limited: #{ex.message}"
rescue ex : OpenAI::BadRequestError
  puts "Bad request: #{ex.message}"
rescue ex : OpenAI::APIError
  puts "API error: #{ex.message}"
end

OpenAI-Compatible Providers

This client supports OpenAI-compatible APIs through a provider extension system. Providers allow you to override types and methods that differ from the OpenAI spec.

Using the DeepSeek Provider

require "openai"
require "openai/providers/deepseek"

# Create a DeepSeek client
client = OpenAI::Providers::DeepSeek::Client.new(
  api_key: ENV["DEEPSEEK_API_KEY"]
)

# List models (uses DeepSeek-compatible types)
models = client.list_models
models.data.each { |m| puts m.id }

# Chat completions work the same as OpenAI
request = OpenAI::CreateChatCompletionRequest.new(model: "deepseek-chat")
  .add_system_message("You are a helpful assistant")
  .add_user_message("Hello!")

response = client.create_chat_completion(request)
puts response.choices.first.message.content

# Streaming also works
request.stream = true
client.create_chat_completion_stream(request) do |chunk|
  chunk.choices.each do |choice|
    if content = choice.delta.content
      print content
    end
  end
end

Creating a Custom Provider

To add support for another OpenAI-compatible API, create a provider module:

# src/openai/providers/my_provider.cr

require "../client"
require "../types"

module OpenAI
  module Providers
    module MyProvider
      BASE_URL = "https://api.myprovider.com/v1"

      # Override types that differ from OpenAI
      # Example: MyProvider doesn't return `created` timestamp for models
      class Model
        include JSON::Serializable

        property id : String
        
        @[JSON::Field(emit_null: false)]
        property created : Int64?  # Make optional
        
        property object : String
        property owned_by : String

        def initialize(
          @id : String = "",
          @created : Int64? = nil,
          @object : String = "model",
          @owned_by : String = ""
        )
        end
      end

      class ListModelsResponse
        include JSON::Serializable

        property object : String
        property data : Array(Model)

        def initialize(
          @object : String = "list",
          @data : Array(Model) = [] of Model
        )
        end
      end

      # Create a client that inherits from OpenAI::Client
      class Client < OpenAI::Client
        def initialize(
          api_key : String = ENV["MY_PROVIDER_API_KEY"]? || "",
          base_url : String = BASE_URL,
          timeout : Time::Span = OpenAI::Client::DEFAULT_TIMEOUT,
          organization : String? = nil
        )
          super(
            api_key: api_key,
            base_url: base_url,
            timeout: timeout,
            organization: organization
          )
        end

        # Override methods that need different return types
        def list_models : ListModelsResponse
          path = "/models"
          response = request("GET", path)
          ListModelsResponse.from_json(response.body)
        end
      end
    end
  end
end

Provider Extension Guidelines

1. Only override what's different - Most endpoints work without changes
2. Use @[JSON::Field(emit_null: false)] - For optional fields not in the provider's response
3. Inherit from OpenAI::Client - Get all standard functionality for free
4. Use protected methods - request() and request_stream() are available to subclasses
5. Add conversion methods - For interoperability with standard OpenAI types

Known Provider Differences

Provider	Differences
DeepSeek	Model.created not returned in /models
Groq	TBD
Together	TBD
Anthropic	Different API structure (not directly compatible)

API Coverage

The client covers all OpenAI API endpoints organized by category:

Category	Endpoints	Description
Chat	12	Chat completions, including streaming
Completions	1	Legacy text completions
Embeddings	1	Text embeddings
Images	3	Image generation and editing
Audio	3	Speech, transcription, translation
Files	5	File upload and management
Fine-tuning	13	Model fine-tuning
Assistants	23	Assistants API
Models	3	Model listing and info
Moderations	1	Content moderation
Batch	4	Batch processing
Uploads	4	Large file uploads
Vector Stores	16	Vector storage for RAG
Evals	12	Model evaluations

Development

Regenerating the Client from OpenAPI Spec

The client is auto-generated from the OpenAPI specification. To regenerate after updating the spec:

Quick Rebuild

crystal run build.cr

Full Rebuild with Validation

# 1. Remove old generated files (keeps providers/)
rm -rf src/openai/api src/openai/types src/openai/client.cr src/openai/error.cr \
       src/openai/multipart.cr src/openai/streaming.cr src/openai/types.cr
rm -rf spec/openai

# 2. Regenerate from OpenAPI spec
crystal run build.cr

# 3. Format generated code
crystal tool format src/openai/ spec/

# 4. Verify compilation
crystal build src/openai.cr --no-codegen

# 5. Run tests
crystal spec

# 6. Test examples
crystal run examples/completion.cr --no-codegen

Customizing the Generator

The build.cr generator can be modified for custom needs:

# Key areas in build.cr:

# Type mapping (line ~380)
# - Modify how OpenAPI types map to Crystal types

# Endpoint parsing (line ~1000)  
# - Customize how API methods are generated

# Chat helpers (line ~1730)
# - Add/modify convenience methods for chat

# Client generation (line ~2200)
# - Customize HTTP client behavior

Project Structure

src/openai/
  client.cr       # Main HTTP client (generated)
  types.cr        # All generated types (2480+)
  error.cr        # Error hierarchy (generated)
  multipart.cr    # Multipart form encoding (generated)
  streaming.cr    # SSE streaming support (generated)
  api/            # API methods by category (generated)
    chat.cr
    embeddings.cr
    ...
  types/          # Type references by category (generated)
    chat.cr
    embeddings.cr
    ...
  providers/      # Provider extensions (NOT generated, manually maintained)
    deepseek.cr
    ...

build.cr          # Code generator
openapi.documented.yml  # OpenAPI specification

Running Tests

# Install dependencies
shards install

# Run all tests
crystal spec

# Run specific test file
crystal spec spec/openai/types/chat_spec.cr

Running Examples

# Set API keys
export OPENAI_API_KEY="your-openai-key"
export DEEPSEEK_API_KEY="your-deepseek-key"

# Run examples
crystal run examples/completion.cr
crystal run examples/image.cr
crystal run examples/deepseek.cr
crystal run examples/list_models.cr

Contributing

Please read CONTRIBUTING.md for details on our code of conduct and the process for submitting pull requests.

Contributing a Provider

1. Create src/openai/providers/your_provider.cr
2. Add an example in examples/your_provider.cr
3. Document differences in the README
4. Submit a PR

Support

• Issues: Use the GitHub Issues for bug reports and feature requests
• Discussions: For questions and discussions, use GitHub Discussions

License

This project is licensed under the MIT License - see the LICENSE file for details.

Changelog

See CHANGELOG.md for a list of changes.

Contributors

• Dominic Sisneros - creator and maintainer

Acknowledgments

• OpenAI for their comprehensive API
• The Crystal community for excellent tooling and support
• All contributors who help improve this project