httpstat.us
A super simple service for generating different HTTP codes. It's useful for testing how your own scripts deal with varying responses. Just add the status code you want to the URL.
HTTP & Headers
HTTP Status
Bulk URL Redirect checker to easily check status codes, response headers, and redirect chains.
Requestly
Intercept & modify network requests. Main features include Modifying headers, Setting up redirects, Switch hosts, inserting custom scripts & much more