OpenAPI Tooling

Spec authoring

• OpenAPI 3.1 — the current spec; JSON Schema 2020-12 compatible.
• JSON Schema — typically generated from your code (Zod, Valibot, ArkType, Effect Schema all have OpenAPI/JSON Schema converters).
• TypeSpec (Microsoft) — TS-flavored language that compiles to OpenAPI / JSON Schema / Protobuf.
• Stoplight Studio — visual OpenAPI editor; free.
• Swagger Editor — original; bundled into many CLIs.

Reference / docs renderers

• ★ Scalar — modern, beautiful, fast; embeds in any framework or runs standalone. The default for new projects in 2026.
• Stoplight Elements — open source web component for OpenAPI; mature.
• Redoc — open source; clean design; long-running classic.
• Swagger UI — the original; functional, dated styling.
• Mintlify — paid hosted docs with OpenAPI integration.
• Bump.sh — hosted API docs with diffs and changelog.

TS client codegen (spec → typed client)

• ★ Hey API (@hey-api/openapi-ts) — modern OpenAPI → TS client; the default for new projects.
• ★ openapi-typescript — generates .d.ts only; pair with openapi-fetch for a typed wrapper.
• OpenAPI Generator — the universal "generate client/server in 50 languages" tool.
• swagger-typescript-api — older but still used.
• Orval — generates Axios / Fetch / TanStack Query / SWR / Zod from OpenAPI.
• oazapfts — small, ergonomic TS client gen.

Server-side: schema-first frameworks

• ★ Hono OpenAPI + Zod — @hono/zod-openapi exposes typed routes with auto-generated OpenAPI.
• tRPC's OpenAPI plugin — for hybrid tRPC + REST.
• oRPC — RPC + OpenAPI from one definition; see Backend.
• NestJS — @nestjs/swagger decorators.
• Fastify — @fastify/swagger from JSON Schema.
• Elysia — built-in OpenAPI from typed routes.

Validation / testing from spec

• Schemathesis — property-based testing from OpenAPI; finds bugs your hand-written tests miss.
• Dredd — verify implementation matches docs.
• Spectral (Stoplight) — lint OpenAPI specs (style, naming, security rules).
• Optic — compare actual API traffic to your spec.

Mocking from spec

• Prism (Stoplight) — mock server from any OpenAPI spec.
• Mockoon — desktop GUI for mocks; OpenAPI import.
• MSW — uses your handler code; can also load OpenAPI fixtures.

Pick this if…

• Default API reference UI: Scalar.
• TS client from a third-party API: Hey API or openapi-typescript + openapi-fetch.
• Schema-first new API in TS: Hono + @hono/zod-openapi, or NestJS, or Elysia.
• Lint / govern your OpenAPI: Spectral.
• Test API matches spec: Schemathesis.
• Mock a third-party API: Prism or MSW.