Speakeasy
Takes an OpenAPI spec and generates polished, type-safe client SDKs across multiple languages, Terraform providers, and MCP servers for AI agent integration. Handles pagination, retries, webhooks, and streaming out of the box. Increasingly positioning itself as the API platform for the agent era.
Swagger / OpenAPI
Swagger UI is the canonical open-source renderer for interactive API documentation from OpenAPI specs, with 28k+ GitHub stars. SwaggerHub adds collaborative API design, versioning, and governance at scale. The de facto standard for REST API specification across the industry.