How do I fix broken or incorrect syntax highlighting in Vim?

Explanation

Vim's syntax highlighting engine does not always parse the entire file from the beginning — it uses sync points to determine where to start parsing for the visible portion of the screen. In large files or files with complex nested syntax (like long strings, heredocs, or embedded languages), this can cause highlighting to break, showing incorrect colors or treating code as a string.

How it works

• :syntax sync fromstart tells Vim to always parse syntax highlighting from the very first line of the file, rather than guessing a sync point near the visible area
• This guarantees correct highlighting at the cost of slightly slower redraw in very large files
• The change applies only to the current buffer

Example

You are editing a large Python file with multi-line strings. After scrolling, everything below a triple-quoted string appears highlighted as a string:

" Fix the broken highlighting immediately
:syntax sync fromstart

To make this permanent for specific file types, add it to your vimrc:

" Always sync from start for Python files
autocmd FileType python syntax sync fromstart

Tips

• For a quick one-time refresh without changing sync behavior, use :syntax sync minlines=200 to increase the sync lookback range instead
• If highlighting breaks frequently, the root cause may be a flawed syntax plugin — :syntax sync fromstart is a reliable workaround
• This can slow down scrolling in files with thousands of lines; if performance matters, use :syntax sync minlines=500 as a compromise