# Access-Control-Request-Headers header

The HTTP **`Access-Control-Request-Headers`** [request header](https://developer.mozilla.org/en-US/docs/Glossary/request%20header) is used by browsers when issuing a [preflight request](https://developer.mozilla.org/en-US/docs/Glossary/preflight%20request) to let the server know which [HTTP headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers) the client might send when the actual request is made (such as with [fetch()](https://developer.mozilla.org/en-US/docs/Web/API/Window%2Ffetch) or [XMLHttpRequest.setRequestHeader()](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/setRequestHeader)). The complementary server-side header of [Access-Control-Allow-Headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Headers) will answer this browser-side header.

<table class="properties">
  <tbody>
    <tr>
      <th scope="row">Header type</th>
      <td>[Request header](https://developer.mozilla.org/en-US/docs/Glossary/Request%20header)</td>
    </tr>
    <tr>
      <th scope="row">[Forbidden request header](https://developer.mozilla.org/en-US/docs/Glossary/Forbidden%20request%20header)</th>
      <td>Yes</td>
    </tr>
  </tbody>
</table>

## Syntax

```http
Access-Control-Request-Headers: <header-name>,<header-name>,…
```

## Directives

- `<header-name>`
  - : A sorted list of unique, comma-separated, lowercase [HTTP headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers) that are included in the request.

## Examples

```http
Access-Control-Request-Headers: content-type,x-pingother
```

## Specifications

## Browser compatibility

## See also

- [Access-Control-Request-Method](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Request-Method)