# Hey API — Generate Production-Ready SDKs from OpenAPI Specs

> An open-source tool that turns OpenAPI and Swagger specifications into type-safe client SDKs, validators, mocks, and more for TypeScript and Python projects.

## Install

Save in your project root:

# Hey API — Generate Production-Ready SDKs from OpenAPI Specs

## Quick Use
```bash
# Install the CLI
npx @hey-api/openapi-ts -i https://petstore3.swagger.io/api/v3/openapi.json -o src/client
# Or add to your project
npm install @hey-api/client-fetch
npx @hey-api/openapi-ts -i ./openapi.yaml -o src/client -c @hey-api/client-fetch
```

## Introduction
Hey API is an open-source code generation tool that transforms OpenAPI and Swagger specifications into type-safe client SDKs. It produces clean, human-readable TypeScript or Python code with full type safety, eliminating the boilerplate of manually writing API clients.

## What Hey API Does
- Generates fully typed API client code from OpenAPI 2.0, 3.0, and 3.1 specifications
- Produces runtime validators using Zod, Valibot, or Arktype from API schemas
- Creates mock data generators for testing based on API response schemas
- Supports multiple HTTP clients including Fetch, Axios, and custom adapters
- Offers a plugin architecture for extending code generation behavior

## Architecture Overview
Hey API processes OpenAPI specification files through a multi-stage pipeline: parsing, intermediate representation, and code generation. The core parser normalizes different OpenAPI versions into a unified IR. Plugins then operate on this IR to produce client code, validators, types, or mocks. The output is tree-shakeable, so bundlers only include the endpoints your code actually uses.

## Self-Hosting & Configuration
- Install `@hey-api/openapi-ts` as a dev dependency in your project
- Point the CLI at a local file or remote URL for your OpenAPI spec
- Configure output directory and client library in `hey-api.config.ts`
- Select plugins for validators, mocks, or framework-specific integrations
- Run code generation as part of your build pipeline or CI

## Key Features
- Clean, human-readable generated code that looks hand-written
- Tree-shakeable output for minimal bundle size
- Plugin system for Zod schemas, mock data, TanStack Query, and more
- Support for multiple HTTP client backends
- Active maintenance with millions of weekly npm downloads

## Comparison with Similar Tools
- **openapi-generator** — supports many languages but produces verbose, hard-to-read code
- **openapi-typescript** — types-only, no runtime client or validators
- **Orval** — generates React Query hooks but less flexible plugin system
- **swagger-codegen** — the original generator, now legacy and less maintained
- **Kiota** — Microsoft's generator, focused on Graph API patterns

## FAQ
**Q: Which OpenAPI versions does Hey API support?**
A: It supports OpenAPI 2.0 (Swagger), 3.0, and 3.1 specifications.

**Q: Can I use Hey API with a non-TypeScript project?**
A: Hey API primarily targets TypeScript. Python support is available through community plugins. Other languages should use openapi-generator.

**Q: How do I keep generated code up to date?**
A: Run the CLI as a build step or CI job. When your OpenAPI spec changes, re-run generation and commit the updated client code.

**Q: Does Hey API support authentication?**
A: Yes. It generates typed auth configuration based on the security schemes defined in your OpenAPI spec.

## Sources
- https://github.com/hey-api/hey-api
- https://heyapi.dev

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Source: https://tokrepo.com/en/workflows/asset-096bc676
Author: AI Open Source