trpc-to-openapi

trpc-to-openapi

OpenAPI support for tRPC 🧩

• Support for tRPC ^11.1.0
• Easy REST endpoints for your tRPC procedures.
• Perfect for incremental adoption.
• Supports all OpenAPI versions.

Note: This project is a fork of a fork, with full credit to the original authors. It appears that the original author has abandoned the project, so I plan to add new features in the near future.

Usage

1. Install trpc-to-openapi.

# pnpm
pnpm add trpc-to-openapi
# npm
npm install trpc-to-openapi
# yarn
yarn add trpc-to-openapi

2. Add OpenApiMeta to your tRPC instance.

import { initTRPC } from '@trpc/server';
import { OpenApiMeta } from 'trpc-to-openapi';

const t = initTRPC.meta<OpenApiMeta>().create(); /* 👈 */

3. Enable openapi support for a procedure.

export const appRouter = t.router({
  sayHello: t.procedure
    .meta({ /* 👉 */ openapi: { method: 'GET', path: '/say-hello' } })
    .input(z.object({ name: z.string() }))
    .output(z.object({ greeting: z.string() }))
    .query(({ input }) => {
      return { greeting: `Hello ${input.name}!` };
    }),

  getStatus: t.procedure
    .meta({ /* 👉 */ openapi: { method: 'GET', path: '/status' } })
    .output(z.object({ status: z.string() }))
    .query(() => {
      return { status: 'healthy' };
    });
});

4. Generate an OpenAPI document.

import { generateOpenApiDocument } from 'trpc-to-openapi';

import { appRouter } from '../appRouter';
import { UserSchema, ProductSchema } from '../schemas';

/* 👇 */
export const openApiDocument = generateOpenApiDocument(appRouter, {
  title: 'tRPC OpenAPI',
  version: '1.0.0',
  baseUrl: 'http://localhost:3000',
  defs: {
    UserSchema,
    ProductSchema,
  },
});

5. Add an trpc-to-openapi handler to your app.

We currently support adapters for Express, Next.js, Fastify, Nuxt & Node:HTTP.

Fetch, Cloudflare Workers & more soon™, PRs are welcomed 🙌.

No support for AWS lambdas

import http from 'http';
import { createOpenApiHttpHandler } from 'trpc-to-openapi';

import { appRouter } from '../appRouter';

const server = http.createServer(createOpenApiHttpHandler({ router: appRouter })); /* 👈 */

server.listen(3000);

6. Profit 🤑

// client.ts
const res = await fetch('http://localhost:3000/say-hello?name=OpenAPI', { method: 'GET' });
const body = await res.json(); /* { greeting: 'Hello OpenAPI!' } */

const statusRes = await fetch('http://localhost:3000/status', { method: 'GET' });
const statusBody = await statusRes.json(); /* { status: 'healthy' } */

Requirements

Peer dependencies:

• tRPC Server v11 (@trpc/server) must be installed.
• Zod v4 (zod@^4.0.0) must be installed.

For a procedure to support OpenAPI the following must be true:

• An output parser is present AND uses Zod validation.
• If an input parser is present, it must use Zod validation.
• Query input parsers (when present) extend Object<{ [string]: String | Number | BigInt | Date }> or Void.
• Mutation input parsers (when present) extend Object<{ [string]: AnyType }> or Void.
• meta.openapi.method is GET, POST, PATCH, PUT or DELETE.
• meta.openapi.path is a string starting with /.
• meta.openapi.path parameters (when present) exist in input parser as String | Number | BigInt | Date

Please note:

• Data transformers (such as superjson) are ignored.
• Trailing slashes are ignored.
• Routing is case-insensitive.

HTTP Requests

Procedures with a GET/DELETE method will accept inputs via URL query parameters. Procedures with a POST/PATCH/PUT method will accept inputs via the request body with a application/json content type.

Path parameters

A procedure can accept a set of inputs via URL path parameters. You can add a path parameter to any OpenAPI procedure by using curly brackets around an input name as a path segment in the meta.openapi.path field.

Query parameters

Query & path parameter inputs are always accepted as a string. This library will attempt to coerce your input values to the following primitive types out of the box: number, boolean, bigint and date. If you wish to support others such as object, array etc. please use z.preprocess().

// Router
export const appRouter = t.router({
  sayHello: t.procedure
    .meta({ openapi: { method: 'GET', path: '/say-hello/{name}' /* 👈 */ } })
    .input(z.object({ name: z.string() /* 👈 */, greeting: z.string() }))
    .output(z.object({ greeting: z.string() }))
    .query(({ input }) => {
      return { greeting: `${input.greeting} ${input.name}!` };
    });
});

// Client
const res = await fetch('http://localhost:3000/say-hello/Lily?greeting=Hello' /* 👈 */, {
  method: 'GET',
});
const body = await res.json(); /* { greeting: 'Hello Lily!' } */

Request body

// Router
export const appRouter = t.router({
  sayHello: t.procedure
    .meta({ openapi: { method: 'POST', path: '/say-hello/{name}' /* 👈 */ } })
    .input(z.object({ name: z.string() /* 👈 */, greeting: z.string() }))
    .output(z.object({ greeting: z.string() }))
    .mutation(({ input }) => {
      return { greeting: `${input.greeting} ${input.name}!` };
    });
});

// Client
const res = await fetch('http://localhost:3000/say-hello/Lily' /* 👈 */, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ greeting: 'Hello' }),
});
const body = await res.json(); /* { greeting: 'Hello Lily!' } */

Custom headers

Any custom headers can be specified in the meta.openapi.requestHeaders and meta.openapi.responseHeaders zod object schema, these headers will not be validated. Please consider using Authorization for first-class OpenAPI auth/security support.

HTTP Responses

Status codes will be 200 by default for any successful requests. In the case of an error, the status code will be derived from the thrown TRPCError or fallback to 500.

You can modify the status code or headers for any response using the responseMeta function.

Please see error status codes here.

Authorization

To create protected endpoints, add protect: true to the meta.openapi object of each tRPC procedure. By default, you can then authenticate each request with the createContext function using the Authorization header with the Bearer scheme. If you wish to authenticate requests using a different/additional methods (such as custom headers, or cookies) this can be overwritten by specifying securitySchemes object.

Explore a complete example here.

Server

import { TRPCError, initTRPC } from '@trpc/server';
import { OpenApiMeta } from 'trpc-to-openapi';

type User = { id: string; name: string };

const users: User[] = [
  {
    id: 'usr_123',
    name: 'Lily',
  },
];

export type Context = { user: User | null };

export const createContext = async ({ req, res }): Promise<Context> => {
  let user: User | null = null;
  if (req.headers.authorization) {
    const userId = req.headers.authorization.split(' ')[1];
    user = users.find((_user) => _user.id === userId);
  }
  return { user };
};

const t = initTRPC.context<Context>().meta<OpenApiMeta>().create();

export const appRouter = t.router({
  sayHello: t.procedure
    .meta({ openapi: { method: 'GET', path: '/say-hello', protect: true /* 👈 */ } })
    .input(z.void()) // no input expected
    .output(z.object({ greeting: z.string() }))
    .query(({ input, ctx }) => {
      if (!ctx.user) {
        throw new TRPCError({ message: 'User not found', code: 'UNAUTHORIZED' });
      }
      return { greeting: `Hello ${ctx.user.name}!` };
    }),
});

Client

const res = await fetch('http://localhost:3000/say-hello', {
  method: 'GET',
  headers: { Authorization: 'Bearer usr_123' } /* 👈 */,
});
const body = await res.json(); /* { greeting: 'Hello Lily!' } */

Examples

For advanced use-cases, please find examples in our complete test suite.

With Express

Please see full example here.

import { createExpressMiddleware } from '@trpc/server/adapters/express';
import express from 'express';
import { createOpenApiExpressMiddleware } from 'trpc-to-openapi';

import { appRouter } from '../appRouter';

const app = express();

app.use('/api/trpc', createExpressMiddleware({ router: appRouter }));
app.use('/api', createOpenApiExpressMiddleware({ router: appRouter })); /* 👈 */

app.listen(3000);

With Next.js app router

Please see full example here.

// src/app/[...trpc]/route.ts
import { appRouter } from '~/server/api/root';
import { createContext } from '~/server/api/trpc';
import { type NextRequest } from 'next/server';
import { createOpenApiFetchHandler } from 'trpc-to-openapi';

export const dynamic = 'force-dynamic';

const handler = (req: NextRequest) => {
  // Handle incoming OpenAPI requests
  return createOpenApiFetchHandler({
    endpoint: '/',
    router: appRouter,
    createContext: () => createContext(req),
    req,
  });
};

export {
  handler as GET,
  handler as POST,
  handler as PUT,
  handler as PATCH,
  handler as DELETE,
  handler as OPTIONS,
  handler as HEAD,
};

With Next.js pages router

Please see full example here.

// pages/api/[...trpc].ts
import { createOpenApiNextHandler } from 'trpc-to-openapi';

import { appRouter } from '../../server/appRouter';

export default createOpenApiNextHandler({ router: appRouter });

With Fastify

Please see full example here.

import { fastifyTRPCPlugin } from '@trpc/server/adapters/fastify';
import Fastify from 'fastify';
import { fastifyTRPCOpenApiPlugin } from 'trpc-to-openapi';

import { appRouter } from './router';

const fastify = Fastify();

async function main() {
  await fastify.register(fastifyTRPCPlugin, { router: appRouter });
  await fastify.register(fastifyTRPCOpenApiPlugin, { router: appRouter }); /* 👈 */

  await fastify.listen({ port: 3000 });
}

main();

Types

GenerateOpenApiDocumentOptions

Please see full typings here.

Property	Type	Description	Required
title	string	The title of the API.	true
description	string	A short description of the API.	false
version	string	The version of the OpenAPI document.	true
baseUrl	string	The base URL of the target server.	true
docsUrl	string	A URL to any external documentation.	false
tags	string[]	A list for ordering endpoint groups.	false
securitySchemes	Record<string, SecuritySchemeObject>	Defaults to Authorization header with Bearer scheme	false
filter	(ctx: { metadata: { openapi: NonNullable<OpenApiMeta['openapi']> } & TMeta }) => boolean	Optional filter function to include/exclude procedures from the generated OpenAPI document.	false

OpenApiMeta

Please see full typings here.

Property	Type	Description	Required	Default
enabled	boolean	Exposes this procedure to trpc-to-openapi adapters and on the OpenAPI document.	false	true
method	HttpMethod	HTTP method this endpoint is exposed on. Value can be GET, POST, PATCH, PUT or DELETE.	true	undefined
path	string	Pathname this endpoint is exposed on. Value must start with /, specify path parameters using {}.	true	undefined
protect	boolean	Requires this endpoint to use a security scheme.	false	true
summary	string	A short summary of the endpoint included in the OpenAPI document.	false	undefined
description	string	A verbose description of the endpoint included in the OpenAPI document.	false	undefined
tags	string[]	A list of tags used for logical grouping of endpoints in the OpenAPI document.	false	undefined
requestHeaders	AnyZodObject	A zod object schema describing any custom headers to add to the request for this endpoint in the OpenAPI document.	false	undefined
responseHeaders	AnyZodObject	A zod object schema describing any custom headers to add to the response for this endpoint in the OpenAPI document.	false	undefined
successDescription	string	A string to use as the description for a successful response.	false	'Successful response'
errorResponses	number[] | { [key: number]: string }	A list of error response codes or an object of response codes and their description to add to the responses for this endpoint.	false	undefined
contentTypes	OpenApiContentType[]	A set of content types specified as accepted in the OpenAPI document.	false	['application/json']
deprecated	boolean	Whether or not to mark an endpoint as deprecated	false	false

CreateOpenApiNodeHttpHandlerOptions

Please see full typings here.

Property	Type	Description	Required
router	Router	Your application tRPC router.	true
createContext	Function	Passes contextual (ctx) data to procedure resolvers.	false
responseMeta	Function	Returns any modifications to statusCode & headers.	false
onError	Function	Called if error occurs inside handler.	false
maxBodySize	number	Maximum request body size in bytes (default: 100kb).	false

License

Distributed under the MIT License. See LICENSE for more information.

Filtering Procedures in OpenAPI Output

You can use the filter option to selectively include or exclude procedures from the generated OpenAPI document. The filter function receives a context object with the procedure's metadata. Return true to include the procedure, or false to exclude it.

Example:

const appRouter = t.router({
  publicProc: t.procedure
    .meta({ openapi: { method: 'GET', path: '/public' }, isPublic: true })
    .input(z.object({}))
    .output(z.object({ result: z.string() }))
    .query(() => ({ result: 'public' })),
  privateProc: t.procedure
    .meta({ openapi: { method: 'GET', path: '/private' }, isPublic: false })
    .input(z.object({}))
    .output(z.object({ result: z.string() }))
    .query(() => ({ result: 'private' })),
});

// Only include procedures where isPublic is true
const openApiDocument = generateOpenApiDocument(appRouter, {
  ...defaultDocOpts,
  filter: ({ metadata }) => metadata.isPublic === true,
});

// openApiDocument.paths will only include '/public'

You can also pass a metadata generic to generateOpenApiDocument to get proper types for your custom metadata in the filter function:

// Define your custom metadata type
interface MyMeta {
  isPublic: boolean;
}

const openApiDocument = generateOpenApiDocument<MyMeta>(appRouter, {
  ...defaultDocOpts,
  filter: ({ metadata }) => metadata.isPublic === true,
});