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MD009 - No Trailing Spaces

This rule checks for trailing spaces at the end of lines.

Why This Rule Exists

Trailing spaces are usually unintentional and can cause issues:

  • They're invisible in most editors, making them hard to spot
  • They can cause unexpected behavior in version control systems
  • They may render differently across different markdown processors
  • They increase file size unnecessarily

Examples

❌ Incorrect (violates rule)

This line has trailing spaces   ← spaces
This one has a tab at the end	← tab
Multiple spaces here    ← spaces

(Where arrows indicate invisible whitespace characters)

✅ Correct

This line has no trailing spaces
This one is clean too
Two spaces for line break are allowed  
when configured (br_spaces = 2)

Configuration

[MD009]
br_spaces = 2  # Number of trailing spaces allowed for line breaks (default: 2)
strict = false # If true, disallow even configured line break spaces (default: false)

Automatic Fix

This rule supports automatic fixing. The fix will:

  • Remove all trailing whitespace from lines
  • Preserve configured line break spaces (typically 2 spaces)
  • Maintain the line's content and structure

When to Disable

Consider disabling this rule if:

  • Your project intentionally uses trailing spaces for formatting

Rule Details

  • Rule ID: MD009
  • Aliases: no-trailing-spaces
  • Category: Whitespace
  • Severity: Warning
  • Automatic Fix: ✅ Available

Configuration Options

[MD009]
br_spaces = 2  # Number of spaces allowed for line breaks (default: 2)
strict = false # If true, disallow even configured line break spaces (default: false)

Understanding Line Breaks

Markdown supports two types of line breaks:

Hard Line Break (Two Spaces)

First line  
Second line on new line

Renders as:

First line
Second line on new line

Paragraph Break (Blank Line)

First paragraph

Second paragraph

Renders as:

First paragraph

Second paragraph

Common Issues and Solutions

Invisible Trailing Spaces

Problem: Spaces at line ends are invisible in most editors.

This line has spaces    ← invisible spaces
Another line with tab	← invisible tab

Solution: Configure your editor to show whitespace or use the automatic fix.

This line has no trailing spaces
Another clean line

Inconsistent Line Break Handling

Problem: Different markdown processors handle trailing spaces differently.

Some text   
More text    
Final text

Solution: Use exactly two spaces for line breaks when needed.

Some text  
More text  
Final text

Editor Configuration

Visual Studio Code

Add to settings.json:

{
  "files.trimTrailingWhitespace": true,
  "markdown.preview.breaks": true,
  "[markdown]": {
    "files.trimTrailingWhitespace": false
  }
}

Vim

Add to .vimrc:

" Show trailing spaces
set list listchars=trail:·

" Remove trailing spaces on save
autocmd BufWritePre * %s/\s\+$//e

Sublime Text

Add to preferences:

{
  "trim_trailing_white_space_on_save": true,
  "draw_white_space": ["all"]
}

Version Control Considerations

Git Configuration

Configure Git to warn about trailing whitespace:

git config core.whitespace trailing-space

Pre-commit Hooks

Use a pre-commit hook to catch trailing spaces:

#!/bin/sh
# .git/hooks/pre-commit
exec git diff --check --cached

When Line Break Spaces Are Needed

Sometimes two trailing spaces are intentional:

Poetry and Verses

Roses are red  
Violets are blue  
Markdown is great  
And so are you

Addresses

123 Main Street  
Suite 100  
Anytown, ST 12345

Preserving Formatting

Name:     John Doe  
Email:    john@example.com  
Phone:    555-1234

Performance Impact

Trailing spaces can impact:

  1. File Size: Unnecessary whitespace increases file size
  2. Diff Noise: Changes to trailing spaces clutter version control
  3. Search/Replace: Invisible characters can break patterns
  4. Copy/Paste: Trailing spaces may cause unexpected behavior

Automatic Fix Behavior

The automatic fix will:

  1. Remove all trailing whitespace from each line
  2. Preserve exactly br_spaces spaces when configured (default: 2)
  3. Handle tabs and mixed whitespace
  4. Maintain line endings (LF/CRLF)

Fix Examples

Before:

Text with spaces    
Text with tab	
Text with mixed

After (default config):

Text with spaces
Text with tab
Text with mixed

After (br_spaces=2, preserving line breaks):

Paragraph text
Line break needed  
Next line
  • MD010 - Hard tabs
  • MD012 - Multiple consecutive blank lines
  • MD047 - Files should end with a single newline

References