I thought this tool wouldn't get much traffic. Mojang's restrictions seemed reasonable - 600 requests per 10 minutes? That's a request every second; no way I'll reach that load. Except I am reaching that load. All the time. Apparently if you Google search "Minecraft Name History" this is one of the first few results. That's what I get for spreading the word, I guess.
Caching isn't a trivial problem - there are all sorts of nuances with Mojang changing offensive names before the 30 day period, etc, and I don't even have anywhere to cache information to. I hacked the script together in an hour in really horribly written PHP code that should never be in any production environment. It's not worth the effort to me when other tools exist and work better.
I don't want people finding a broken dysfunctional service at the top of their Google search results - it's an inconvenience to everyone. So I've decided: I'm shutting down this service. It was great while it worked, but other services exist that have solved the caching problem in their own ways. Just use Google to find them - they're right under my result (for now - hopefully my result fades away).
The source code will always be available on GitHub.