I use Fiddler extensively. It’s one of the few tools that I honestly don’t think I could do my job without.
A few good use cases:
- Any time redirects are involved … like with authentication systems with multiple redirects for one request. You can see step by step what’s happening.
- Cookies … rather than just checking your browser tools to see what cookies have been set, just check out the response headers and see exactly where they where and by what they were set.
- Caching. Viewing cache headers is huge. Not to mention to see whether a request for a resource was actually made to the server, or just served from cache.
- Ajax. Obviously, it helps to see what you are sending a receiving.
- Tracking code … is your beacon request being sent?
- Basically any time there is a front end issue with your web page, fiddler can usually help … are all the resources you’re expecting being included? Is there a funny third-party request from your page that you don’t recognize? Are there 404’s on any of your resources… etc.
- Pausing requests and responses. This is helpful if you want to test a SPOF for a file, or performance.
- Editing requests and responses. Is there an obfuscated js file on a page that you want to debug, but can’t because it’s all on a single line? No worries, pause the response, copy the script into a js beautifier, edit the response by adding the beautified js, and viola, you can now debug.
You can manipulate requests and responses programatically, which is a new thing I recently discovered… which is way more useful than I would have anticipated. http://www.fiddler2.com/fiddler/dev/scriptsamples.asp
- Highlight requests that have certain text or headers … (like requests that set a certain cookie, etc.)
- Simulate delays
- Pause particular responses so you can edit (or test SPOF)
- Return a 404 or 500 on certain resources to test how your app will handle it
- Add / Remove headers
- You can record a session and use it to load testing.
- You can use it to test a REST api by creating your own requests from scratch.
- You can reply requests and sessions over again without actually using your browser.
There’s other good tools out there that can accomplish the same thing, and Fiddler is admittedly not the most intuitive program. But just like Eclipse, once you figure it out, you’ll love it.
Bah! This took longer than 10 minutes … i might have to bump my description up to 15 :/