# tRPC

URL: https://tailrace.dev/docs/reference/trpc

> Reference for @tailrace/trpc - createTailraceMiddleware, withTrpc, and TailraceTrpcOptions.



`@tailrace/trpc` provides procedure middleware for `@trpc/server`. It scans procedure input and result data at the tool boundary (not an OpenAI REST gateway).

## Install [#install]

```bash
pnpm add @tailrace/core @tailrace/trpc @trpc/server
```

Peer dependency: `@trpc/server` `>=10` (bound against `@trpc/server@11.x`). Depends on `@tailrace/core` + [`@tailrace/adapter`](/docs/reference/adapter) (not `@tailrace/http`).

## Exports [#exports]

| Export                     | Description                                            |
| -------------------------- | ------------------------------------------------------ |
| `createTailraceMiddleware` | Standalone middleware for `t.procedure.use(...)`       |
| `withTrpc`                 | Attach fluent `middleware(...)` to a Tailrace instance |
| `TailraceTrpcOptions`      | Options type                                           |
| `TrpcMiddlewareContext`    | Context passed to option resolvers                     |
| `TailraceWithTrpc`         | Fluent instance type                                   |

## Options [#options]

| Option       | Default          | Notes                          |
| ------------ | ---------------- | ------------------------------ |
| `agent`      | `"default"`      | `string` or `(info) => string` |
| `name`       | procedure `path` | Tool name for the boundary     |
| `workflowId` | `"default"`      | `string` or `(info) => string` |
| `onDecision` | -                | Audit callback                 |

## Surfaces [#surfaces]

| Surface | Boundary                                   | Behavior                                              |
| ------- | ------------------------------------------ | ----------------------------------------------------- |
| Input   | `{ kind: "tool", name, direction: "out" }` | `check` before `next`; rewrite input on tokenize/mask |
| Output  | `{ kind: "tool", name, direction: "in" }`  | `check` ok result data; rewrite on tokenize/mask      |
| Block   | -                                          | Throw `TRPCError` (`BAD_REQUEST`), value-free message |

Streaming procedures are out of scope in v0.1 (non-streaming queries/mutations only).

## See also [#see-also]

* [Govern tRPC procedures](/docs/guides/govern-trpc-procedures)
* [tRPC integration](/docs/integrations/trpc)
* [`PolicyViolationError`](/docs/reference/errors/POLICY_VIOLATION)