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The Codegen Project - 8 Months of Progress

· 4 min read
Jonas Lagoni
Jonas Lagoni
The Codegen Project creator

I am way to good at working in the shadows... Since our last update at v0.39.0, the project has grown substantially. Spanning versions v0.40.0 through v0.62.1 and brings complete OpenAPI support, a powerful HTTP client support, and an MCP server for AI integration.

TLDR:

  • MCP server to give AI assistants project context
  • Full OpenAPI/Swagger support (payloads, parameters, headers, types, channels)
  • Comprehensive HTTP client protocol with auth, OAuth2, pagination, retry, and hooks
  • JSON Schema support (models and custom generators)
  • Watch mode, WebSocket channels, and many more improvements...

MCP Server for AI Integration​

Perhaps the most exciting addition is the MCP (Model Context Protocol) server. This gives AI assistants like Claude, Cursor, and others deep context about The Codegen Project - its generators, protocols, configuration options, and best practices.

Why does this matter? Deterministic code generation and AI are complementary. The MCP server bridges these worlds by helping AI assistants create the right context for the task at hand.

This means you can ask your AI assistant to "set up NATS messaging from my AsyncAPI spec" and it will use The Codegen Project to generate consistent, tested code - then help you implement the business logic on top.

Complete OpenAPI Support​

The Codegen Project now fully supports OpenAPI (Swagger 2.0, OpenAPI 3.0, and 3.1) specifications:

// codegen.config.mjs
export default {
  inputType: 'openapi',
  inputPath: './openapi.json',
  language: 'typescript',
  generators: [
    { preset: 'payloads', outputPath: './src/models' },
    { preset: 'parameters', outputPath: './src/params' },
    { preset: 'headers', outputPath: './src/headers' },
    { preset: 'types', outputPath: './src/types' },
    { preset: 'channels', outputPath: './src/api', protocols: ['http_client'] }
  ]
};

Most of the generators you know from AsyncAPI now work with OpenAPI - payloads with validation, typed parameters and headers, and HTTP-specific channel functions.

HTTP Client Protocol Refactor​

The HTTP client protocol received a major overhaul with enterprise-grade features:

Authentication:

  • API Key (header, query, cookie)
  • HTTP Basic/Bearer authentication
  • OAuth2 flows (client credentials, password, implicit, authorization code)
  • Automatic token refresh

Resilience:

  • Configurable retry with exponential backoff
  • Request/response hooks for logging, metrics, and custom logic
  • Abort controller support for cancellation

Pagination:

  • Cursor-based pagination
  • Offset pagination
  • Link-header pagination
  • Automatic iteration helpers
// Generated code with full type safety
const response = await getUsers({
  parameters: { page: 1, limit: 10 },
  auth: { type: 'bearer', token: 'your-token' },
  retry: { maxRetries: 3, backoffMs: 1000 }
});

JSON Schema Input Processor​

You can now generate models directly from JSON Schema files:

export default {
  inputType: 'jsonschema',
  inputPath: './schema.json',
  language: 'typescript',
  generators: [
    { preset: 'models', outputPath: './src/models' }
  ]
};

This supports Draft-4, Draft-6, and Draft-7 specifications.

Other Notable Improvements​

Watch Mode - Automatically regenerate code when your spec changes:

codegen generate --watch
codegen generate --watch --watchPath ./specs

WebSocket Channels - Full WebSocket support with publish, subscribe, and register patterns for bidirectional messaging.

MQTT Subscribe - Complete MQTT subscription functionality with QoS support.

Headers Across Protocols - NATS, Kafka, MQTT, AMQP, and WebSocket all now support typed headers when defined in your spec.

Types Generator - Generate simple type definitions without full model classes.

Models Generator - Generate complex data models using Modelina integration.

Telemetry - Anonymous usage tracking to help improve the project (easily disabled via CODEGEN_TELEMETRY_DISABLED=true).

Improved Channel Structure - Protocol implementations are now split into separate files for better maintainability.

This release represents a significant expansion of The Codegen Project's capabilities. Whether you're working with AsyncAPI, OpenAPI, or JSON Schema - and whether you're building messaging systems or REST APIs - the tooling is now more comprehensive than ever.

The MCP server integration particularly excites us as it validates the vision: deterministic code generation and AI working together, each doing what they do best.

Give v0.62.1 a try, and let us know what you think!

Until next time, happy coding!