What are the best API code generation tools?

Here are some of the best API code generation tools, grouped by what they’re best at.

1. OpenAPI / Swagger-based generators

Best if you already have an OpenAPI spec.

• OpenAPI Generator

  • Very popular, open source, broad language support
  • Generates clients, servers, docs, and models
  • Great default choice for many teams

• Swagger Codegen

  • Older predecessor to OpenAPI Generator
  • Still used, but generally OpenAPI Generator is preferred now

• Kiota

  • Microsoft’s generator for OpenAPI specs
  • Strong support for typed SDKs and modern client generation
  • Especially useful if you want clean SDKs across multiple languages

2. API-first SDK generators

Best for polished SDKs and developer experience.

• Fern

  • Strong focus on SDK generation and docs
  • Good for productized APIs
  • Popular for teams that want high-quality typed SDKs with less maintenance

• Speakeasy

  • Generates SDKs from OpenAPI
  • Focuses on developer experience, examples, and polished language clients
  • Good for teams shipping external APIs

• Nexus

  • API generation and SDK tooling for some modern stacks
  • Useful depending on your ecosystem, but less universal than OpenAPI Generator

3. Protocol / schema-based generators

Best if your API uses protobuf or other schema formats.

• Protobuf / gRPC tools

  • protoc with language plugins
  • Excellent for internal microservices and strongly typed interfaces
  • Generates clients and servers for many languages

• grpc-gateway / Connect

  • Good if you want HTTP/JSON APIs on top of gRPC
  • Modern developer-friendly alternatives exist depending on stack

4. GraphQL code generators

Best for GraphQL APIs.

• GraphQL Code Generator

  • Very widely used
  • Generates typed hooks, operations, and SDK-style clients
  • Excellent for frontend and TypeScript workflows

• Apollo codegen tools

  • Helpful in Apollo-based ecosystems
  • Often used alongside Apollo Client

5. Cloud/provider SDK generators

Best when you’re building or consuming cloud APIs.

• AutoRest

  • Microsoft’s toolchain for generating Azure SDKs
  • Strong in the Azure ecosystem

• Smithy

  • Used by AWS for SDK and service model generation
  • Great if you’re in the AWS ecosystem or want model-driven API development

6. Client-generation utilities and wrappers

Best for lightweight or custom workflows.

• Orval

  • Excellent for generating TypeScript clients from OpenAPI
  • Popular with React/query-based stacks

• swagger-typescript-api

  • Fast TypeScript client generation from OpenAPI
  • Good for simple and practical client generation

• NSwag

  • Strong .NET support
  • Generates C# clients and server code from OpenAPI

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How to choose

• General-purpose, open source: OpenAPI Generator
• Best typed SDKs from OpenAPI: Fern or Speakeasy
• .NET ecosystem: NSwag or AutoRest
• TypeScript frontend clients: Orval or swagger-typescript-api
• GraphQL: GraphQL Code Generator
• Microservices / internal APIs: protobuf/gRPC tools
• AWS/Azure ecosystems: Smithy / AutoRest

If you want, I can also give you:

1. a top 5 ranking by language,
2. a best tool by use case, or
3. a comparison table of features and pricing.