openapi-typescript is a monorepo of developer tools for consuming OpenAPI 3.x schemas in TypeScript. It provides a CLI and Node.js API to convert any valid OpenAPI specification (3.0/3.1) into TypeScript type definitions (interfaces, unions, enums) with zero runtime overhead. The generated types are used by companion packages: openapi-fetch, a tiny (~6 kB) type-safe fetch client with full parameter serialization, middleware pipeline, and custom serializer support; and openapi-react-query, a ~1 kB wrapper around @tanstack/react-query that provides typed hooks (useQuery, useMutation, useInfiniteQuery, useSuspenseQuery) with automatic query key inference. The monorepo also includes openapi-typescript-helpers, a shared package of utility types (Readable, Writable, FilterKeys, etc.) consumed by the other packages. The architecture is a pnpm workspace with Turborepo orchestration, Biome for linting/formatting, unbuild for package building, and Changesets for versioning. The core code generator (packages/openapi-typescript) uses the TypeScript Compiler API to build AST nodes directly, supporting an extensive set of options (enums, immutable types, path-params-as-types, read/write markers, root types, etc.). The fetch client (packages/openapi-fetch) implements full OpenAPI parameter serialization styles, a middleware system with onRequest/onResponse/onError lifecycle hooks, and a path-based client proxy for ergonomic endpoint access. All packages are thoroughly tested with unit tests, snapshot tests against real-world APIs (GitHub, Stripe, DigitalOcean), and e2e tests using Playwright. The repository includes comprehensive documentation (English, Japanese, Chinese) with a VitePress site, framework examples (Next.js, SvelteKit, Vue 3), and benchmarking against alternatives. The project is actively maintained with a large community (8.4k stars, 287 open issues, 672 forks) and is used in production by companies such as Netlify, Supabase, Google Firebase CLI, and GitHub Octokit.