The project I am working on at the time of the post has many rewrite rules that a request has to go through before being served.

Problems sometimes occur due to incorrect regex, new features that should be handled by rule N but get caught by rule Y and many other cases.

Having hundreds of rules it’s very hard to spot which one is the culprit - in comes Failed Requests Using Tracing.

I found this guide helpful setting it up on the project - FREB IIS

Make sure you setup Rewrite at the Trace Provider and after you are done debugging, switch off FREB as it might impact disk space over time.

  • if you don’t see Rewrite option, you have to repair your IIS URL Rewrite module

FREB Rewrite Trace Provider

You might encounter permission issue when FREB tries to create the logs folder. What worked for me was to setup Full Control permissions to IIS_USRS, IISUSR, Network Service and also manually create the …\logs\FailedReqLogFiles\ folder.

Permission Issue