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I embarrassed myself today (yelling at the work desk, telling everyone I'd take them to McDonalds) but with good cause: a tool I wrote some time back made it to Scott Hanselman's 2007 Ultimate Developer/Power User Tools List. The goal of the tool was simple: to do browser based evaluation of regular expressions using the .NET engine. Prior to writing it I would frequent Rexv.org but because the engines supported there were different, I'd usually have to do some conversion to get things to the .NET world.
There are quite a few .NET Regular Expression tools: Expresso, which is my first and favorite since I've used it longest, but also tools like Roy Osherove's The Regulator. The problem with these tools, however, was that as fat clients I wasn't always easily able to use them: I work on different machines (home, work, client sites) and also assist people quite a bit away from my desk.
There are also quite a few Regular Expression tools for the web, Rexv, which I mentioned before but also RegexPal. But these tools support either javascript or alternate implementations so patterns like (?<foo>\w+) usually return some kind of error.
The way Nregex works is pretty straight forward: I'm using YUI for the Ajax library and working with the .NET implementation of the regular expression on the server. A simultaneous goal of mine is to get into more of YUI because I'm always building little knick-knacks in javascript and I think it's the library to beat right now.
Of course it's a fledgling: I worked on it a few nights when I could and fixed bugs here are there when I had a moment. Please use it and give me feedback since that will be my biggest help in making it better.
One more thing: I'm trying to collect useful regular expressions. I'd like to build a good library of expressions to help users of the tool. Use the feedback form and let me know if you've got one you've found handy. Don't worry if it's not .NET specific, I'll do the translation.