# Custom header YAML reference
<a name="custom-header-YAML-format"></a>

Specify custom headers using the following YAML format:

```
customHeaders:
  - pattern: '*.json'
    headers:
    - key: 'custom-header-name-1'
      value: 'custom-header-value-1'
    - key: 'custom-header-name-2'
      value: 'custom-header-value-2'
  - pattern: '/path/*'
    headers:
    - key: 'custom-header-name-1'
      value: 'custom-header-value-2'
```

For a monorepo, use the following YAML format:

```
applications:
  - appRoot: app1
    customHeaders:
    - pattern: '**/*'
      headers:
      - key: 'custom-header-name-1'
        value: 'custom-header-value-1'
  - appRoot: app2
    customHeaders:
    - pattern: '/path/*.json'
      headers:
      - key: 'custom-header-name-2'
        value: 'custom-header-value-2'
```

When you add custom headers to your app, you will specify your own values for the following:

**pattern**  
Custom headers are applied to all URL file paths that match the pattern.

**headers**  
Defines the headers that match the file pattern.

**key**  
The name of the custom header.

**value**  
The value of the custom header.

To learn more about HTTP headers, see Mozilla's list of [HTTP Headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers).