How do I profile Vimscript functions to find what is slowing down Vim at runtime?

Explanation

When Vim feels sluggish during editing—not just at startup—you need runtime profiling to pinpoint which functions are consuming the most time. The :profile command instruments Vimscript function calls, measuring both self time and total time for each invocation, then writes a detailed log you can analyze.

How it works

• :profile start profile.log begins profiling and sets the output file where results will be written
• :profile func * tells Vim to profile every function call (you can replace * with a specific pattern like MyPlugin* to narrow the scope)
• After reproducing the slow behavior, run :profile stop or quit Vim to flush the results
• Open profile.log to see a sorted breakdown of function call counts, total time, and self time

Example

" Start profiling all functions
:profile start /tmp/profile.log
:profile func *

" Optionally, also profile scripts (sourced files)
:profile file *

" Now do the slow operation...
" When done, stop profiling
:profile stop

The output log looks like:

FUNCTIONS SORTED ON SELF TIME
count  total (s)   self (s)  function
  142   1.235678   0.987654  MySlowFunction()
   38   0.456789   0.345678  StatusLineUpdate()
    5   0.123456   0.098765  SyntaxHighlightCheck()

Tips

• Use :profile func MyPlugin* to narrow profiling to specific functions, reducing overhead
• The self time column is usually most useful—it shows time spent in the function itself, excluding calls to other functions
• Combine with :profile file * to also see which script files are slow during sourcing
• This is the runtime complement to vim --startuptime which only measures startup