MD020 - No Space Inside Hashes on Closed ATX Style Heading

Severity: Warning
Category: Headings
Auto-fix: ✓ Available

Rule Description

This rule ensures closed ATX-style headings have no spaces inside the closing hashes. Closed ATX headings use trailing hash characters for symmetry, and spaces inside these markers are incorrect.

Why This Rule Exists

Proper closed heading format is important because:

Follows the ATX heading specification
Maintains consistent heading style
Prevents parsing issues with some markdown processors
Ensures visual symmetry in closed headings

Examples

❌ Incorrect (violates rule)

# Heading with space before closing #
## Another heading ##  
### Heading with spaces ###

✅ Correct

# Heading with proper closing #
## Another heading ##
### Correctly closed heading ###
# Open heading is also fine

Configuration

This rule has no configuration options.

Automatic Fix

This rule supports automatic fixing with --fix. The fix will:

Remove spaces between heading content and closing hashes
Preserve the heading level and content
Maintain the closed heading style

Apply Fix

# Fix closed heading spacing
mdbook-lint lint --fix docs/

# Preview what would be fixed
mdbook-lint lint --fix --dry-run docs/

When to Disable

Consider disabling this rule if:

You prefer open ATX headings (without closing hashes)
Your markdown processor has different requirements for closed headings

Disable in Config

# .mdbook-lint.toml
disabled_rules = ["MD020"]

Disable Inline

<!-- mdbook-lint-disable MD020 -->
# Heading with space # 
<!-- mdbook-lint-enable MD020 -->

MD018 - No space after hash on ATX heading
MD019 - Multiple spaces after hash on ATX heading
MD021 - Multiple spaces inside hashes on closed ATX heading
MD022 - Headings should be surrounded by blank lines
MD003 - Heading style

mdbook-lint Documentation