How do I generate strongly typed API clients?

To generate strongly typed API clients, the usual approach is:

1. Describe the API with a machine-readable contract

   • Most commonly:
     • OpenAPI/Swagger for REST APIs
     • gRPC/protobuf for RPC APIs
     • GraphQL schema for GraphQL APIs

2. Use a code generator

   • The generator reads the contract and emits client code with:
     • typed request/response models
     • typed method signatures
     • enums / discriminated unions where supported
     • validation helpers in some generators

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Common options by API style

REST APIs

OpenAPI is the standard.

Popular generators:

• OpenAPI Generator
• Swagger Codegen
• NSwag (.NET, TypeScript)
• Kiota (Microsoft, multi-language)
• orval (TypeScript/React Query)
• openapi-typescript (TS types only)
• openapi-fetch (typed fetch client for TS)

Example workflow:

1. Write or export openapi.yaml
2. Run generator
3. Import generated client into your app

Example:

openapi-generator-cli generate -i openapi.yaml -g typescript-fetch -o ./client

This can produce code like:

const api = new PetApi();
const pets = await api.listPets();

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gRPC APIs

Use protobuf definitions.

Generate strongly typed clients with:

• protoc
• language-specific plugins

Example:

protoc --ts_out=./client --plugin=protoc-gen-ts=...

This gives you typed request/response messages and service stubs.

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GraphQL APIs

Use the GraphQL schema and operations.

Popular tools:

• GraphQL Code Generator
• Apollo codegen

These generate:

• typed query/mutation result types
• typed variables
• typed hooks in frontend frameworks

Example:

graphql-codegen

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Best practices for strong typing

• Keep the API contract as the source of truth
• Generate models from the contract, rather than hand-writing them
• Version your API schema
• Use enums and oneOf/anyOf carefully for better type narrowing
• Add runtime validation if you need safety beyond compile-time types
• Regenerate clients in CI when the contract changes

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If you’re using TypeScript

The most common choices are:

• openapi-typescript → generates types from OpenAPI
• openapi-fetch → lightweight typed HTTP client
• orval → generates clients + hooks
• GraphQL Code Generator → for GraphQL

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Quick recommendation

• REST + TypeScript: openapi-typescript or orval
• REST + many languages: OpenAPI Generator
• gRPC: protoc
• GraphQL: GraphQL Code Generator

If you want, I can show you a step-by-step example for your stack, like:

• TypeScript + REST
• Python
• Java/Kotlin
• C#
• Go