## Debugging syntax files

Syntax files are often the cause for slowdowns due to wrong and/or complex
regular expressions. If the `+profile` [feature](#what-kind-of-vim-am-i-running)
is compiled in, Vim provides the super useful `:syntime` command.

```vim
:syntime on
" hit <c-l> a few times to redraw the window which causes the syntax rules to get applied again
:syntime off
:syntime report
```

The output contains important metrics. E.g. you can see which regexp takes too
long and should be optimized or which regexps are used all the time but never
even match.

See `:h :syntime`.