This is great. I want a tool like this for other languages.

I don't get it, isn't it doing a basic find/replace that is available in any reasonable editor?

It is doing something a little smarter than that, as gofmt understands the language it is parsing it rather than just a textual find/replace.

The interesting thing here is that you can make your other tools use this, it makes writing tools around go a lot easier.

Yeah I know what gofmt does, it's useful for code formatting and getting you 95% of the way there on api changes but in the slide presentation linked above he mostly just replaces method names and things of that nature.