wsdjeg-vim-galore-zh_cn/chapter/Debugging-Syntax-Files.md

Debugging syntax files

Syntax files are often the cause for slowdowns due to wrong and/or complex regular expressions. If the +profile feature is compiled in, Vim provides the super useful :syntime command.

: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.