Validated at runtime, not just typed at compile time.

Install npm install -D @codewithagents/openapi-gen

Tested against 128 real-world specs (Stripe, GitHub, Spotify, OpenAI) in CI on every commit.

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See it in action

Real output from the Petstore 3.0 spec, generated by the toolchain and committed to the repo. This is what CI compiles on every PR.

Fetch client

// client.ts — auto-generated by @codewithagents/openapi-gen
import type { Pet, Order } from './models.js'
import { getConfig, type ClientConfig } from './client-config.js'
import { z } from 'zod'
import { PetSchema, OrderSchema } from './schemas.js'

export class ApiError extends Error {
  constructor(
    public readonly status: number,
    public readonly body: unknown
  ) {
    super(`API error ${status}`)
    this.name = 'ApiError'
  }
}

// Validates both request and response bodies at runtime against Zod schemas.
export async function addPet(body: Pet, config?: Partial<ClientConfig>): Promise<Pet> {
  PetSchema.parse(body)
  const res = await _request('POST', '/pet', { body }, config)
  return PetSchema.parse(await res.json())
}

export async function findPetsByStatus(
  params: { status: 'available' | 'pending' | 'sold' },
  config?: Partial<ClientConfig>
): Promise<Pet[]> {
  const searchParams = new URLSearchParams()
  if (params?.status != null) searchParams.set('status', String(params.status))
  const res = await _request('GET', '/pet/findByStatus', { searchParams }, config)
  return z.array(PetSchema).parse(await res.json())
}

Types

// models.ts — auto-generated by @codewithagents/openapi-gen
import type { z } from 'zod'
import type {
  OrderSchema,
  CategorySchema,
  UserSchema,
  TagSchema,
  PetSchema,
  ApiResponseSchema,
} from './schemas.js'

export type Order = z.infer<typeof OrderSchema>
export type Category = z.infer<typeof CategorySchema>
export type User = z.infer<typeof UserSchema>
export type Tag = z.infer<typeof TagSchema>
export type Pet = z.infer<typeof PetSchema>
export type ApiResponse = z.infer<typeof ApiResponseSchema>

Zod schemas

// schemas.ts — bootstrapped by @codewithagents/openapi-gen, then yours to extend.
// Re-running the generator will NOT overwrite this file.
import { z } from 'zod'

export const TagSchema = z
  .object({ id: z.number().optional(), name: z.string().optional() })
  .passthrough()

export const PetSchema = z
  .object({
    id: z.number().optional(),
    name: z.string(),
    category: z.object({ id: z.number().optional(), name: z.string().optional() }).optional(),
    photoUrls: z.array(z.string()),
    tags: z.array(TagSchema).optional(),
    status: z.enum(['available', 'pending', 'sold']).optional(),
  })
  .passthrough()

export const OrderSchema = z
  .object({
    id: z.number().optional(),
    petId: z.number().optional(),
    quantity: z.number().optional(),
    status: z.enum(['placed', 'approved', 'delivered']).optional(),
    complete: z.boolean().optional(),
  })
  .passthrough()

React Query hooks

// hooks.ts — auto-generated by @codewithagents/openapi-react-query
import { useQuery, type UseQueryOptions, useMutation } from '@tanstack/react-query'
import { addPet, findPetsByStatus, getPetById, type ApiError } from './client.js'

export const petKeys = {
  findPetsByStatus: (params: Parameters<typeof findPetsByStatus>[0]) =>
    ['pet', 'findPetsByStatus', params] as const,
  detail: (petId: string) => ['pet', petId] as const,
}

export function useFindPetsByStatus(
  params: Parameters<typeof findPetsByStatus>[0],
  options?: Omit<
    UseQueryOptions<Awaited<ReturnType<typeof findPetsByStatus>>, ApiError>,
    'queryKey' | 'queryFn'
  >
) {
  return useQuery<Awaited<ReturnType<typeof findPetsByStatus>>, ApiError>({
    queryKey: petKeys.findPetsByStatus(params),
    queryFn: () => findPetsByStatus(params),
    staleTime: 0,
    gcTime: 300000,
    ...options,
  })
}

// Path-param hooks set enabled: false when id is nullish — no boilerplate at call sites.
export function useGetPetById(
  petId: string | undefined | null,
  options?: Omit<
    UseQueryOptions<Awaited<ReturnType<typeof getPetById>>, ApiError>,
    'queryKey' | 'queryFn'
  >
) {
  return useQuery<Awaited<ReturnType<typeof getPetById>>, ApiError>({
    queryKey: petKeys.detail(petId!),
    queryFn: () => getPetById(petId!),
    enabled: petId != null && (options?.enabled ?? true),
    ...options,
  })
}

Server interface

// service.ts — auto-generated by @codewithagents/openapi-server
import type { Order, Pet, User } from './models.js'

export interface SwaggerPetstoreOpenAPI30Service {
  /** POST /pet */
  addPet(body: Pet): Promise<Pet>
  /** PUT /pet */
  updatePet(body: Pet): Promise<Pet>
  /** GET /pet/findByStatus */
  findPetsByStatus(params: { status: string }): Promise<Pet[]>
  /** GET /pet/{petId} */
  getPetById(petId: string): Promise<Pet>
  /** DELETE /pet/{petId} */
  deletePet(petId: string): Promise<void>
  /** POST /store/order */
  placeOrder(body: Order): Promise<Order>
  /** GET /user/{username} */
  getUserByName(username: string): Promise<User>
}

Generates clean, type-safe code from real-world specs like:

• Stripe
• GitHub
• Spotify
• OpenAI
• Adyen
• + 123 more in CI

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The pipeline

Each package is independent, but they compose. A single OpenAPI spec drives everything from server contract to form field error UX.

One source of truth. When the spec changes, re-run the generators and the compiler tells you exactly what broke.

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Packages

@codewithagents/openapi-gen

Types, fetch client, and Zod schemas from your OpenAPI spec. Learn more

@codewithagents/openapi-react-query

React Query v5 hooks, generated. Learn more

@codewithagents/openapi-server

Typed service interface and optional router for Hono, Express, or Fastify. Learn more

@codewithagents/api-errors

Map API errors to form field errors. Learn more

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Why this toolkit

Validated, not just typed

Generate Zod schemas from your spec, then enable runtime validation with one config field (input_schema). The fetch client checks both request and response bodies against your schemas, so bugs surface at the boundary, not deep in your UI.

Proven on 128 real specs

Stripe, GitHub, Spotify, OpenAI, Adyen, AWS, and more. Every spec is generated and compiled in CI on every commit. Not benchmarked once and forgotten.

Code you own

Output is plain TypeScript files in your repo. No runtime black box, no proprietary client to call into. Adjust, extend, delete. The compiler is your upgrade guide.

OpenAPI 3.1 first-class

Full support for $ref, allOf, anyOf, oneOf, nullable, and 3.1.1 keyword changes. 3.0.x is supported in practice: 8 of our 13 showcase specs are 3.0.x and all compile. A few 3.0-only constructs like nullable are not yet normalized to 3.1 semantics. No Swagger 2.0.

Native fetch. Zero added bundle weight.

The generated client uses only native fetch. No axios, no wrapper libraries. Nothing from the codegen packages ends up in your bundle.

ESM, strict mode, Prettier-ready

Every generated file compiles with strict: true and "type": "module". Output passes prettier --check with your own config.

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Up and running in minutes

1. Install the generator.

   npm install -D @codewithagents/openapi-gen

   For React Query hooks, also add:

   npm install -D @codewithagents/openapi-react-query && npm install @tanstack/react-query

2. Create a config file in your project root.

   {
     "input_openapi": "./openapi.json",
     "output": "./src/api"
   }

   Point input_openapi at your spec (JSON or YAML, local path or URL). The output directory is created automatically.

3. Run the generator and import the output.

   npx openapi-gen

   Then use the generated barrel directly:

   import { configureClient, getPetById, useFindPetsByStatus } from './src/api'
   
   configureClient({ baseUrl: 'https://petstore3.swagger.io/api/v3' })
   
   const pet = await getPetById('1')
   const { data, isLoading } = useFindPetsByStatus({ status: 'available' })

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Is this for you?

Use it when

• You build in TypeScript and want end-to-end type safety from a single spec.
• You want to own the generated code, not call into a runtime black box.
• Your spec is large, real-world, or full of edge cases. The toolkit is tested against 128 real-world specs (Stripe, GitHub, Spotify, OpenAI, and more) on every PR, so there is a strong chance your edge cases are already covered. The gnarlier your spec, the more that matters.
• You want validation and form-field error UX, not just static types. Zod schemas plus api-errors carry correctness all the way from the spec to the UI.

Look elsewhere if

• You need a non-TypeScript target. Output is TypeScript only. Python, Go, Java, and other language clients are out of scope.
• Your spec is OpenAPI 2.0 / Swagger. Only OpenAPI 3.x is supported. No Swagger 2.0.
• You want a managed runtime SDK. The generated code is yours to own, not a library you call into, so there is no built-in retry, pagination, or caching layer.
• You need a hosted GUI or dashboard. The toolchain is a CLI plus npm packages.

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Built with this toolkit

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Get started

Quickstart

Go from a spec file to a working typed client in five minutes. Read the quickstart

GitHub

Source code, issues, and the compatibility matrix across 128 specs. View on GitHub