# Hono

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

> OpenAI-compatible Hono middleware - scan chat bodies and SSE streams, return 422 on policy block.



Enforce data policy on OpenAI-compatible chat routes in Hono. Scan request messages before upstream, scan JSON and SSE responses on the way back.

## Quickstart [#quickstart]

```ts
import { createTailrace } from "@tailrace/core";
import { tailraceHono } from "@tailrace/hono";
import { Hono } from "hono";

const app = new Hono();
const tailrace = createTailrace();

app.use(
  "/v1/*",
  tailraceHono(tailrace, {
    agent: (c) => c.req.header("x-agent-id") ?? "default",
    workflowId: (c) => c.req.header("x-workflow-id") ?? "default",
  }),
);
```

Peer: `hono` `>=4`. Only `mode: "openai-compatible"` in v0.1.

## Boundaries covered [#boundaries-covered]

| Location                | Tailrace boundary                                   | Direction            |
| ----------------------- | --------------------------------------------------- | -------------------- |
| Chat request messages   | `{ kind: "model", provider }` (`model` field as-is) | Outbound to upstream |
| JSON chat completion    | same model boundary                                 | Inbound              |
| SSE `text/event-stream` | same; carry-buffer across chunks                    | Inbound              |

Block → **422** `{ error: { type: "policy_violation", entity, rule } }`. SSE: cancel upstream, emit one error `data:` event, close (abort-only; no `streamBlockBehavior` in v0.1).

## Guides [#guides]

* [Protect PII in the AI SDK](/docs/guides/protect-pii-in-ai-sdk) - related model-boundary patterns
* [Boundaries](/docs/concepts/boundaries)

## Reference [#reference]

* [Hono package](/docs/reference/hono)