Plain text output for command line user agents

I've just been building a restful API and am testing it with curl.

I have debugtoolbar enabled and 500 errors come through as a full web page which isn't at all easy to read.

The obvious solution is to disable debugtoolbar but it would still be nice to show plain text output for obvious CLI requests eg. `curl`, `wget`, `httpie` in case people use curl with dbtb switched on.

Alternatively there could be a white list of browser user-agents to show HTML response for or use `content-type`, but that all seems error prone.