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.
To add response headers like
Content-Type to your route, go to the route's Headers tab and fill the name and value fields:
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:
And add one or more headers at the bottom of the page: