In Mockoon you can easily define response headers for each route but also at the environment level. Response headers defined on a route will override those defined in an environment.

Route level response headers

To add response headers like Content-Type to your route, go to the route's Headers tab and fill the name and value fields:

Add route response header

Environment level response headers

You can also add response headers at the environment level. Headers defined in an environment will be overridden if they are redefined on a route. To define an environment response header:

Open the Environment Settings by clicking on the cog in the upper right corner:

click on cog icon

And add one or more headers at the bottom of the page:

Add environment response header