---
title: "setResponseCallback( callback ) | Grafana k6 documentation"
description: "set responseCallback to mark responses as expected"
---

> For a curated documentation index, see [llms.txt](/llms.txt). For the complete documentation index, see [llms-full.txt](/llms-full.txt).

# setResponseCallback( callback )

Set the response callback to be called to determine if a response was expected/successful or not.

The result of this is that requests will be tagged with `expected_response` `"true"` or `"false"` and `http_req_failed` will be emitted with the reverse. This does include all redirects so if for a request only 200 is the expected response and there is 301 redirect before that, the redirect will be marked as failed as only status code 200 was marked as expected.

#### Exceptions

Due to implementation specifics:

- Requests with authentication `digest` are always expected to first get 401 and then to get whatever was specified.
- Requests with authentication `ntlm` will let a 401 status code on the first request as well as anything defined by `expectedStatuses`

Expand table

| Parameter | Type                                                                          | Description                                                                                           |
|-----------|-------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------|
| callback  | [expectedStatuses](/docs/k6/latest/javascript-api/k6-http/expected-statuses/) | an object returned from [expectedStatuses](/docs/k6/latest/javascript-api/k6-http/expected-statuses/) |

Currently only the very special [expectedStatuses](/docs/k6/latest/javascript-api/k6-http/expected-statuses/) objects are supported but in the future it is planned that a JavaScript callback will be supported as well. By default requests with status codes between 200 and 399 are considered “expected”.

Setting the callback to `null` disables the tagging with `expected_response` and the emitting of `http_req_failed`.

It is recommended that if a per request responseCallback is used with [Params](/docs/k6/latest/javascript-api/k6-http/params/) it is actually defined once and used instead of creating it on each request.

### Example

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import http from 'k6/http';

http.setResponseCallback(http.expectedStatuses({ min: 200, max: 300 }));

const only300Callback = http.expectedStatuses(300);

export default () => {
  // this will use the default response callback and be marked as successful
  http.get('https://quickpizza.grafana.com/api/status/200');

  // this will be marked as a failed request as it won't get the expected status code of 300
  http.get('https://quickpizza.grafana.com/api/status/200', {
    responseCallback: only300Callback,
  });

  http.setResponseCallback(http.expectedStatuses(301));
  // from here on for this VU only the 301 status code will be successful so on the next iteration of
  // the VU the first request will be marked as failure
};
```