---
description: "The zod schema for the POST body of /api/chat, and the LIMITS it enforces."
---

# `chatRequestSchema`

The zod schema for the POST body of `/api/chat`, and the `LIMITS` it enforces. Counts, sizes and names are capped so a page, or anyone calling the endpoint, cannot send an unbounded prompt. [`createChatHandler`](/docs/reference/chat/create-chat-handler) already applies it; use it when you write your own handler or test a client.

## Import

```ts
import { chatRequestSchema, LIMITS } from "@webmcp-agents/chat/server";
import type { ChatRequest } from "@webmcp-agents/chat/server";
```

`LIMITS` is exported from `@webmcp-agents/chat/server` (and used by the client internally); the main entry does not export it.

## Example

A handler of your own that validates the body first and answers with the first issues.

```ts title="api/chat.ts"
import { chatRequestSchema, LIMITS } from "@webmcp-agents/chat/server";

// A handler of your own: validate the POST body first.
export async function POST(req: Request): Promise<Response> {
  const parsed = chatRequestSchema.safeParse(await req.json());

  if (!parsed.success) {
    return Response.json(
      {
        error: "bad_request",
        issues: parsed.error.issues.slice(0, 10),
      },
      { status: 400 },
    );
  }

  const { messages, tools, agent } = parsed.data;
  console.log(
    `${messages.length}/${LIMITS.messages} messages,`,
    `${tools.length}/${LIMITS.tools} tools, agent: ${agent ?? "none"}`,
  );
  return Response.json({ ok: true });
}
```

## Options

`chatRequestSchema.safeParse(body)` takes the parsed JSON body. Its fields (`ChatRequest`):

| Name | Type | Default | Description |
|---|---|---|---|
| `messages` | `AgentMessage[]` | required | The conversation, 1 to 160. Each has an `id` of 1 to 64 characters, a `role` of `"user"` or `"assistant"` and at most 40 `parts`. |
| `tools` | `{ name, description, inputSchema }[]` | required | The page's tools: at most 48, with unique names. |
| `page` | `{ url?: string }` | not set | Where the conversation happens. `url` is at most 2000 characters; only a same-origin path reaches the model. |
| `agent` | `string` | not set | The agent's id, matching `/^[a-zA-Z0-9_.-]{1,64}$/`, looked up in the handler's registry. An id only: instructions in the body are unknown keys and are stripped. |

### Rules per field

| Field | Rule |
|---|---|
| text part | `text` is at most 8000 characters. |
| reasoning part | `text` is at most 32 000 characters; `providerMetadata` at most 32 000 characters as JSON. |
| tool part | `id` is 1 to 128 characters; `name` matches the tool name rule; `state` is one of the [`ToolCallState`](/docs/reference/chat/adapter-types#toolcallstate)s; `output.content` has at most 20 items; `error` and `prompt` are at most 8000 characters; `providerMetadata` at most 32 000 characters as JSON. A nested `agent` run is not accepted (the cloud adapter strips it). |
| tool `name` | `/^[a-zA-Z0-9_.-]{1,128}$/` |
| tool `description` | At most 1024 characters. |
| tool `inputSchema` | An object, at most 8192 characters as JSON. |

### `LIMITS`

| Key | Value | Meaning |
|---|---|---|
| `bodyBytes` | 1 048 576 | Request body, counted while streaming. |
| `messages` | 160 | Messages per request. The cloud adapter trims the oldest past this. |
| `parts` | 40 | Parts per message. |
| `text` | 8000 | Characters per text, error or prompt. |
| `reasoning` | 32 000 | Characters of reasoning text (and its metadata). |
| `tools` | 48 | Tools per request. |
| `description` | 1024 | Characters per tool description. |
| `schemaBytes` | 8192 | Characters per input schema, as JSON. |

## Returns

`chatRequestSchema.safeParse(body)` gives `{ success: true, data: ChatRequest }` or `{ success: false, error }` with the zod issues. `ChatRequest` is `z.infer<typeof chatRequestSchema>`.

## Notes

- The body size is checked before parsing, by the handler (413), not by the schema.
- A tool output keeps `content` and `isError` only: other keys of a result do not reach the server.
- Only a same-origin path from `page.url` reaches the model, and only for a same-origin browser request.

## See also

- [`createChatHandler`](/docs/reference/chat/create-chat-handler)
- [`createCloudAdapter`](/docs/reference/chat/create-cloud-adapter), the client that builds this body
- [Adapter types](/docs/reference/chat/adapter-types)