> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getmcp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# notifications/cancelled

> Client tells the server an in-flight request should be cancelled — typically because the user hit Stop.

`notifications/cancelled` is a **client → server** notification (no response expected). The client sends it when the user wants to abort an in-flight request — for example, hitting "Stop" while a long-running `tools/call` is mid-execution.

GetMCP records the cancellation against `session_id + request_id` in an in-process registry. Code paths that opt into cancellation can poll the flag and bail early.

***

## Wire-level Shape

```json theme={null}
{
  "jsonrpc": "2.0",
  "method":  "notifications/cancelled",
  "params": {
    "requestId": 42,
    "reason":    "User pressed Stop"
  }
}
```

<ParamField body="params.requestId" type="integer | string" required>
  The `id` of the in-flight request the client wants to cancel.
</ParamField>

<ParamField body="params.reason" type="string">
  Optional human-readable explanation. Logged but not propagated to the upstream API.
</ParamField>

***

## Polling the Flag

Once the cancellation lands, any code on the server can check:

```php theme={null}
use GetMCP\Protocol\CancellationHandler;

if ( CancellationHandler::is_cancelled( $session_id, $request_id ) ) {
    // Abort the loop, close connections, return early.
}
```

`is_cancelled()` is `O(1)` — cheap enough to poll inside a loop iterating over large datasets or pre-flight before each upstream HTTP call.

***

## Caveats

* The built-in `ToolExecutor` is **synchronous**. It does not yet poll `is_cancelled()` mid-flight, so an in-flight `tools/call` will run to completion regardless. The hook is in place — wiring it into the executor's loops is a future change.
* Custom tools authored via the `getmcp_after_tool_call` / `getmcp_before_tool_call` hooks **can** poll the flag manually.
* Cancellation state is cleared automatically when the request completes (success or error) so re-using the same request id later doesn't carry a stale cancel.

***

<Note>
  Cancellation is "best effort" per the spec. The server is not required to honour every cancel signal — it may simply finish the in-flight work and return the result. GetMCP follows this contract.
</Note>