Version: 11.x

HTTP RPC Specification

Methods <-> Type mapping

HTTP Method	Mapping	Notes
`GET`	`.query()`	Input JSON-stringified in query param. e.g. `myQuery?input=${encodeURIComponent(JSON.stringify(input))}`
`POST`	`.mutation()`	Input as POST body.
`GET`	`.subscription()`	Subscriptions are supported via Server-sent Events using `httpSubscriptionLink`, or via WebSockets using `wsLink`.

Accessing nested procedures

Nested procedures are separated by dots, so a request to byId below would end up being a request to /api/trpc/post.byId.

ts
export const appRouter = router({
  post: router({
    byId: publicProcedure.input(String).query(async (opts) => {
      // [...]
    }),
  }),
});

ts
export const appRouter = router({
  post: router({
    byId: publicProcedure.input(String).query(async (opts) => {
      // [...]
    }),
  }),
});

Batching

When batching, we combine all parallel procedure calls of the same HTTP method in one request using a data loader.

The called procedures' names are combined by a comma (,) in the pathname
Input parameters are sent as a query parameter called input which has the shape Record<number, unknown>.
We also need to pass batch=1 as a query parameter.
If the response has different statuses, we send back 207 Multi-Status (e.g., if one call errored and one succeeded)

Batching Example Request

Given a router like this exposed at `/api/trpc`:

server/router.ts
tsx
export const appRouter = t.router({
  postById: t.procedure.input(String).query(async (opts) => {
    const post = await opts.ctx.post.findUnique({
      where: { id: opts.input },
    });
    return post;
  }),
  relatedPosts: t.procedure.input(String).query(async (opts) => {
    const posts = await opts.ctx.findRelatedPostsById(opts.input);
    return posts;
  }),
});

server/router.ts
tsx
export const appRouter = t.router({
  postById: t.procedure.input(String).query(async (opts) => {
    const post = await opts.ctx.post.findUnique({
      where: { id: opts.input },
    });
    return post;
  }),
  relatedPosts: t.procedure.input(String).query(async (opts) => {
    const posts = await opts.ctx.findRelatedPostsById(opts.input);
    return posts;
  }),
});

... And two queries defined like this in a React component:

MyComponent.tsx
tsx
export function MyComponent() {
  const post1 = trpc.postById.useQuery('1');
  const relatedPosts = trpc.relatedPosts.useQuery('1');
 
  return (
    <pre>
      {JSON.stringify(
        {
          post1: post1.data ?? null,
          relatedPosts: relatedPosts.data ?? null,
        },
        null,
        4,
      )}
    </pre>
  );
}

MyComponent.tsx
tsx
export function MyComponent() {
  const post1 = trpc.postById.useQuery('1');
  const relatedPosts = trpc.relatedPosts.useQuery('1');
 
  return (
    <pre>
      {JSON.stringify(
        {
          post1: post1.data ?? null,
          relatedPosts: relatedPosts.data ?? null,
        },
        null,
        4,
      )}
    </pre>
  );
}

The above would result in exactly 1 HTTP call with this data:

Location property	Value
`pathname`	`/api/trpc/postById,relatedPosts`
`search`	`?batch=1&input=%7B%220%22%3A%221%22%2C%221%22%3A%221%22%7D` *

*) input in the above is the result of:

ts
encodeURIComponent(
  JSON.stringify({
    0: '1', // <-- input for `postById`
    1: '1', // <-- input for `relatedPosts`
  }),
);

ts
encodeURIComponent(
  JSON.stringify({
    0: '1', // <-- input for `postById`
    1: '1', // <-- input for `relatedPosts`
  }),
);

Batching Example Response

Example output from server

json
[
  // result for `postById`
  {
    "result": {
      "data": {
        "id": "1",
        "title": "Hello tRPC",
        "body": "..."
        // ...
      }
    }
  },
  // result for `relatedPosts`
  {
    "result": {
      "data": [
        /* ... */
      ]
    }
  }
]

json
[
  // result for `postById`
  {
    "result": {
      "data": {
        "id": "1",
        "title": "Hello tRPC",
        "body": "..."
        // ...
      }
    }
  },
  // result for `relatedPosts`
  {
    "result": {
      "data": [
        /* ... */
      ]
    }
  }
]

HTTP Response Specification

In order to have a specification that works regardless of the transport layer we try to conform to JSON-RPC 2.0 where possible.

Successful Response

Example JSON Response

json
{
  "result": {
    "data": {
      "id": "1",
      "title": "Hello tRPC",
      "body": "..."
    }
  }
}

json
{
  "result": {
    "data": {
      "id": "1",
      "title": "Hello tRPC",
      "body": "..."
    }
  }
}

ts
interface SuccessResponse {
  result: {
    data: TOutput; // output from procedure
  }
}

ts
interface SuccessResponse {
  result: {
    data: TOutput; // output from procedure
  }
}

Error Response

Example JSON Response

json
[
  {
    "error": {
      "json": {
        "message": "Something went wrong",
        "code": -32600, // JSON-RPC 2.0 code
        "data": {
          // Extra, customizable, meta data
          "code": "INTERNAL_SERVER_ERROR",
          "httpStatus": 500,
          "stack": "...",
          "path": "post.add"
        }
      }
    }
  }
]

json
[
  {
    "error": {
      "json": {
        "message": "Something went wrong",
        "code": -32600, // JSON-RPC 2.0 code
        "data": {
          // Extra, customizable, meta data
          "code": "INTERNAL_SERVER_ERROR",
          "httpStatus": 500,
          "stack": "...",
          "path": "post.add"
        }
      }
    }
  }
]

When possible, we propagate HTTP status codes from the error thrown.
If the response has different statuses, we send back 207 Multi-Status (e.g., if one call errored and one succeeded)
For more on errors and how to customize them see Error Formatting.

Error Codes <-> HTTP Status

ts
const HTTP_STATUS_CODES = {
  PARSE_ERROR: 400,
  BAD_REQUEST: 400,
  UNAUTHORIZED: 401,
  PAYMENT_REQUIRED: 402,
  FORBIDDEN: 403,
  NOT_FOUND: 404,
  METHOD_NOT_SUPPORTED: 405,
  TIMEOUT: 408,
  CONFLICT: 409,
  PRECONDITION_FAILED: 412,
  PAYLOAD_TOO_LARGE: 413,
  UNSUPPORTED_MEDIA_TYPE: 415,
  UNPROCESSABLE_CONTENT: 422,
  PRECONDITION_REQUIRED: 428,
  TOO_MANY_REQUESTS: 429,
  CLIENT_CLOSED_REQUEST: 499,
  INTERNAL_SERVER_ERROR: 500,
  NOT_IMPLEMENTED: 501,
  BAD_GATEWAY: 502,
  SERVICE_UNAVAILABLE: 503,
  GATEWAY_TIMEOUT: 504,
} as const;

ts
const HTTP_STATUS_CODES = {
  PARSE_ERROR: 400,
  BAD_REQUEST: 400,
  UNAUTHORIZED: 401,
  PAYMENT_REQUIRED: 402,
  FORBIDDEN: 403,
  NOT_FOUND: 404,
  METHOD_NOT_SUPPORTED: 405,
  TIMEOUT: 408,
  CONFLICT: 409,
  PRECONDITION_FAILED: 412,
  PAYLOAD_TOO_LARGE: 413,
  UNSUPPORTED_MEDIA_TYPE: 415,
  UNPROCESSABLE_CONTENT: 422,
  PRECONDITION_REQUIRED: 428,
  TOO_MANY_REQUESTS: 429,
  CLIENT_CLOSED_REQUEST: 499,
  INTERNAL_SERVER_ERROR: 500,
  NOT_IMPLEMENTED: 501,
  BAD_GATEWAY: 502,
  SERVICE_UNAVAILABLE: 503,
  GATEWAY_TIMEOUT: 504,
} as const;

Error Codes <-> JSON-RPC 2.0 Error Codes

Available codes & JSON-RPC code

ts
/**
 * JSON-RPC 2.0 Error codes
 *
 * `-32000` to `-32099` are reserved for implementation-defined server-errors.
 * For tRPC we're copying the last digits of HTTP 4XX errors.
 */
export const TRPC_ERROR_CODES_BY_KEY = {
  /**
   * Invalid JSON was received by the server.
   * An error occurred on the server while parsing the JSON text.
   */
  PARSE_ERROR: -32700,
  /**
   * The JSON sent is not a valid Request object.
   */
  BAD_REQUEST: -32600, // 400
 
  // Internal JSON-RPC error
  INTERNAL_SERVER_ERROR: -32603, // 500
  NOT_IMPLEMENTED: -32603, // 501
  BAD_GATEWAY: -32603, // 502
  SERVICE_UNAVAILABLE: -32603, // 503
  GATEWAY_TIMEOUT: -32603, // 504
 
  // Implementation specific errors
  UNAUTHORIZED: -32001, // 401
  PAYMENT_REQUIRED: -32002, // 402
  FORBIDDEN: -32003, // 403
  NOT_FOUND: -32004, // 404
  METHOD_NOT_SUPPORTED: -32005, // 405
  TIMEOUT: -32008, // 408
  CONFLICT: -32009, // 409
  PRECONDITION_FAILED: -32012, // 412
  PAYLOAD_TOO_LARGE: -32013, // 413
  UNSUPPORTED_MEDIA_TYPE: -32015, // 415
  UNPROCESSABLE_CONTENT: -32022, // 422
  PRECONDITION_REQUIRED: -32028, // 428
  TOO_MANY_REQUESTS: -32029, // 429
  CLIENT_CLOSED_REQUEST: -32099, // 499
} as const;

ts
/**
 * JSON-RPC 2.0 Error codes
 *
 * `-32000` to `-32099` are reserved for implementation-defined server-errors.
 * For tRPC we're copying the last digits of HTTP 4XX errors.
 */
export const TRPC_ERROR_CODES_BY_KEY = {
  /**
   * Invalid JSON was received by the server.
   * An error occurred on the server while parsing the JSON text.
   */
  PARSE_ERROR: -32700,
  /**
   * The JSON sent is not a valid Request object.
   */
  BAD_REQUEST: -32600, // 400
 
  // Internal JSON-RPC error
  INTERNAL_SERVER_ERROR: -32603, // 500
  NOT_IMPLEMENTED: -32603, // 501
  BAD_GATEWAY: -32603, // 502
  SERVICE_UNAVAILABLE: -32603, // 503
  GATEWAY_TIMEOUT: -32603, // 504
 
  // Implementation specific errors
  UNAUTHORIZED: -32001, // 401
  PAYMENT_REQUIRED: -32002, // 402
  FORBIDDEN: -32003, // 403
  NOT_FOUND: -32004, // 404
  METHOD_NOT_SUPPORTED: -32005, // 405
  TIMEOUT: -32008, // 408
  CONFLICT: -32009, // 409
  PRECONDITION_FAILED: -32012, // 412
  PAYLOAD_TOO_LARGE: -32013, // 413
  UNSUPPORTED_MEDIA_TYPE: -32015, // 415
  UNPROCESSABLE_CONTENT: -32022, // 422
  PRECONDITION_REQUIRED: -32028, // 428
  TOO_MANY_REQUESTS: -32029, // 429
  CLIENT_CLOSED_REQUEST: -32099, // 499
} as const;

Overriding the default HTTP method

To override the HTTP method used for queries/mutations, you can use the methodOverride option:

server/httpHandler.ts
tsx
// Your server must separately allow the client to override the HTTP method
const handler = createHTTPHandler({
  router: router,
  allowMethodOverride: true,
});

server/httpHandler.ts
tsx
// Your server must separately allow the client to override the HTTP method
const handler = createHTTPHandler({
  router: router,
  allowMethodOverride: true,
});

client/trpc.ts
tsx
import { createTRPCClient, httpLink } from '@trpc/client';
import type { AppRouter } from './server';
 
// The client can then specify which HTTP method to use for all queries/mutations
const client = createTRPCClient<AppRouter>({
  links: [
    httpLink({
      url: `http://localhost:3000`,
      methodOverride: 'POST', // all queries and mutations will be sent to the tRPC Server as POST requests.
    }),
  ],
});

client/trpc.ts
tsx
import { createTRPCClient, httpLink } from '@trpc/client';
import type { AppRouter } from './server';
 
// The client can then specify which HTTP method to use for all queries/mutations
const client = createTRPCClient<AppRouter>({
  links: [
    httpLink({
      url: `http://localhost:3000`,
      methodOverride: 'POST', // all queries and mutations will be sent to the tRPC Server as POST requests.
    }),
  ],
});

Dig deeper

You can read more details by drilling into the TypeScript definitions in

Methods <-> Type mapping​

Accessing nested procedures​

Batching​

Batching Example Request​

Given a router like this exposed at /api/trpc:​

... And two queries defined like this in a React component:​

The above would result in exactly 1 HTTP call with this data:​

Batching Example Response​

HTTP Response Specification​

Successful Response​

Error Response​

Error Codes <-> HTTP Status​

Error Codes <-> JSON-RPC 2.0 Error Codes​

Overriding the default HTTP method​

Dig deeper​