How do I find which Vim scripts or functions are slow and causing performance issues?

Explanation

When Vim feels sluggish, the built-in :profile command lets you measure exactly how much time each script and function consumes. It writes detailed timing data to a log file, showing you where time is being spent so you can optimize or remove the offending code.

How it works

• :profile start profile.log — begins profiling and sets the output file
• :profile func * — tells Vim to profile all functions (you can also target specific ones)
• :profile file * — profiles all sourced scripts
• After reproducing the slow behavior, quit Vim and inspect profile.log

A typical profiling session looks like:

:profile start profile.log
:profile func *
:profile file *
" ... do the slow operation ...
:qa

Example

The output file contains per-function and per-line timing:

FUNCTION  MySlowPlugin#highlight()
Called 47 times
Total time:   2.341500
 Self time:   1.892300

count  total (s)   self (s)
   47   1.892300   1.892300   let matches = matchlist(line, pattern)

This reveals that MySlowPlugin#highlight() was called 47 times and consumed 2.3 seconds, with the regex matching line being the bottleneck.

Tips

• For startup profiling, launch Vim with vim --startuptime startup.log — this is separate from :profile and measures plugin load times
• Sort the profile log by Total time to find the biggest offenders
• Use :profile pause and :profile continue to isolate specific operations
• Profile individual functions with :profile func MyFunc instead of * for targeted analysis