# MCP

URL: https://tailrace.dev/docs/integrations/mcp

> Wrap MCP client transports with Tailrace - JSON-RPC error on block, rewrite on tokenize.



Enforce data policy on MCP `tools/call` and `resources/read` without tearing down the transport.

## Quickstart [#quickstart]

```ts
import { createTailrace } from "@tailrace/core";
import { withMcp } from "@tailrace/mcp";

const tailrace = withMcp(createTailrace());
const transport = tailrace.transport(sseTransport, { server: "salesforce" });
```

Peer: `@modelcontextprotocol/sdk` `>=1`.

## Boundaries covered [#boundaries-covered]

| Location                | Tailrace boundary                                        | Direction |
| ----------------------- | -------------------------------------------------------- | --------- |
| `tools/call` arguments  | `{ kind: "mcp", server, tool, direction: "out" }`        | Outbound  |
| `tools/call` result     | same with `direction: "in"`                              | Inbound   |
| `resources/read` result | `{ kind: "mcp", server, tool: "read", direction: "in" }` | Inbound   |

Block → JSON-RPC error `code: -32001` with `{ type: "policy_violation", entity, rule }` (never the raw value).

## Guides [#guides]

* [Govern MCP tool calls](/docs/guides/govern-mcp-tool-calls)
* [Boundaries](/docs/concepts/boundaries)

## Reference [#reference]

* [MCP package](/docs/reference/mcp)