I’ve played around with Firefox’s Greasemonkey add-on here and there but never really delved into it until recently.  I found most of the common uses for it to be either too specific to someone else’s use habits or already covered by other extensions.  For example, there are probably a million ad blocking scripts out there, but I already have Adblock.

I’ve grown to appreciate Greasemonkey a lot more since I learned that you can make AJAX calls in scripts – now we can do some real damage.  But this post is not about that, it’s about a totally different use case that I hadn’t thought of before.

If you’re a web developer with any friends or family you’ve probably heard this one before:

“Something’s wrong with my web site, can you take a look?”

Often, though, you won’t have access to a dev server, database, or even a copy of the server-side code.  All you can see is the HTML and Javascript source and the HTTP transactions going back and forth.

Greasemonkey can’t rewrite PHP code on someone else’s server but it does make it really, really easy for you to alter forms, delete and change cookie values, and patch and debug Javascript on the site you’re looking at, without changing any other variables.

This can be really, really useful in some situations.  So now it’s officially added to my volunteer/web-developer/brother-in-law toolbelt.