How do I highlight trailing whitespace with a custom color in Vim?

Explanation

How it works

Vim's highlight and match commands let you create custom visual indicators. By combining them, you can make trailing whitespace glaringly visible with a colored background.

The setup has two parts:

1. Define a highlight group:

highlight TrailingWhitespace ctermbg=red guibg=red

• TrailingWhitespace is a custom name you choose
• ctermbg=red sets the background color in terminal Vim
• guibg=red sets the background color in GVim/GUI Vim

2. Create a match pattern:

match TrailingWhitespace /\s\+$/

• match links a highlight group to a regex pattern
• \s\+$ matches one or more whitespace characters at the end of a line

For a more robust setup that does not highlight trailing whitespace while you are still typing on the current line, use an autocmd:

autocmd InsertEnter * match TrailingWhitespace /\s\+\%#\@<!$/
autocmd InsertLeave * match TrailingWhitespace /\s\+$/

The \%#\@<! pattern means "not at the cursor position," so trailing spaces on the line you are currently editing are not highlighted until you leave insert mode.

You can also auto-strip trailing whitespace on save:

autocmd BufWritePre * %s/\s\+$//e

Example

Add to your ~/.vimrc:

" Define the highlight color
highlight TrailingWhitespace ctermbg=red guibg=red

" Smart matching: don't highlight current line in insert mode
augroup TrailingSpace
    autocmd!
    autocmd BufWinEnter * match TrailingWhitespace /\s\+$/
    autocmd InsertEnter * match TrailingWhitespace /\s\+\%#\@<!$/
    autocmd InsertLeave * match TrailingWhitespace /\s\+$/
augroup END

Now any line with trailing spaces shows a red highlight at the end. This makes it easy to spot unwanted whitespace that can cause issues in diffs, linters, and code reviews.