Swagger
API DevelopmentTools for designing, building, and documenting RESTful APIs
apidocumentationopenapirest
Tools for designing, building, and documenting RESTful APIs
End-to-end typesafe APIs for TypeScript applications
Fast and Git-friendly open-source API client
Complete API development environment for building and testing APIs
Open-source API client for GraphQL, REST, and gRPC
Collective list of free APIs for development
Open-source API development ecosystem