How do I persistently highlight specific patterns with custom colors in Vim?

Explanation

The matchadd() function lets you add persistent highlights to patterns without affecting the search register. Unlike /pattern, these highlights remain visible even when you search for something else, making them ideal for code review or tracking multiple patterns simultaneously.

How it works

• matchadd({group}, {pattern}) — highlights all matches of {pattern} using highlight group {group}
• Returns a match ID that can be used with matchdelete() to remove it
• Common groups: Search, IncSearch, ErrorMsg, WarningMsg, DiffAdd

Example

:call matchadd('ErrorMsg', '\<TODO\>')
:call matchadd('DiffAdd', '\<DONE\>')

Before: TODO and DONE are plain text
After: TODO highlighted in red, DONE in green (simultaneously)

Tips

• Use :call clearmatches() to remove all custom highlights
• Store the ID: :let m = matchadd('Search', 'pat') then :call matchdelete(m)
• Use matchaddpos() to highlight specific line/column positions instead of patterns
• These highlights are window-local — they only affect the current window