OpenAPI support for tRPC 🧩

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

Usage

1. Install @lilyrose2798/trpc-openapi.

# npm
npm install @lilyrose2798/trpc-openapi
# yarn
yarn add @lilyrose2798/trpc-openapi

2. Add OpenApiMeta to your tRPC instance.

import { initTRPC } from '@trpc/server';
import { OpenApiMeta } from '@lilyrose2798/trpc-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}!` };
    });
});

4. Generate an OpenAPI document.

import { generateOpenApiDocument } from '@lilyrose2798/trpc-openapi';

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

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

5. Add an @lilyrose2798/trpc-openapi handler to your app.

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

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

import http from 'http';
import { createOpenApiHttpHandler } from '@lilyrose2798/trpc-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=Lily', { method: 'GET' });
const body = await res.json(); /* { greeting: 'Hello Lily!' } */

Requirements

Peer dependencies:

• tRPC Server v10 (@trpc/server) must be installed.
• Zod v3 (zod@^3.14.4) must be installed (recommended ^3.20.0).

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

• Both input and output parsers are present AND use Zod validation.
• Query input parsers extend Object<{ [string]: String | Number | BigInt | Date }> or Void.
• Mutation input parsers 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 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 or application/x-www-form-urlencoded 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 '@lilyrose2798/trpc-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 '@lilyrose2798/trpc-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

Please see full example here.

// pages/api/[...trpc].ts
import { createOpenApiNextHandler } from '@lilyrose2798/trpc-openapi';

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

export default createOpenApiNextHandler({ router: appRouter });

With AWS Lambda

Please see full example here.

import { createOpenApiAwsLambdaHandler } from '@lilyrose2798/trpc-openapi';

import { appRouter } from './appRouter';

export const openApi = createOpenApiAwsLambdaHandler({ router: appRouter });

With Fastify

Please see full example here.

import { fastifyTRPCPlugin } from '@trpc/server/adapters/fastify';
import Fastify from 'fastify';
import { fastifyTRPCOpenApiPlugin } from '@lilyrose2798/trpc-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 |

OpenApiMeta

Please see full typings here.

| Property | Type | Description | Required | Default | | -------------------- | --------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------ | -------- | ----------------------- | | enabled | boolean | Exposes this procedure to trpc-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 | false | | 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 |

Still using tRPC v9? See our .interop() example.

License

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