I recently uploaded fast-tags-0.0.3. The main thing is that all the performance problems I was able to find have been fixed---hopefully will no longer be mistaken as an April Fools joke! Here's copy and paste from the hackage description: Changes since 0.0.2: Lots of speed ups, especially when given lots of files at once. Support for type families and GADTs. Support infix operators, multiple declarations per line, and fix various other bugs that missed or gave bad tags. Limitations: No emacs tags, but they would be easy to add. Not using a real haskell parser means there are more likely to be dark corners that don't parse right. Only top-level functions with type declarations are tagged. Top-level functions without type declarations are skipped, as are ones inside let or where. Code has to be indented "properly", so brace and semicolon style with strange dedents will probably confuse it.