MDBOOK004 - No Duplicate Chapter Titles

Chapter titles should be unique across the book.

Why This Rule Exists

Duplicate chapter titles create confusion in navigation and can cause issues with mdBook's URL generation. Each chapter should have a distinct, identifiable title.

Examples

Incorrect (SUMMARY.md)

# Summary

- [Introduction](./intro.md)
- [Getting Started](./start.md)
- [Introduction](./advanced-intro.md)  <!-- Duplicate -->

Correct

# Summary

- [Introduction](./intro.md)
- [Getting Started](./start.md)
- [Advanced Introduction](./advanced-intro.md)

Configuration

[MDBOOK004]
case_sensitive = true                  # Case-sensitive comparison (default: true)
ignore_prefixes = ["Chapter", "Part"]  # Prefixes stripped before comparing (default: none)

• case_sensitive: with the default, "Setup" and "setup" are different titles. Set it to false to treat them as duplicates.
• ignore_prefixes: the first matching prefix is stripped from a title (along with the whitespace after it) before comparison, so "Chapter Setup" and "Setup" compare equal.

When to Disable

• Books with intentionally repeated section names
• Multi-part books where repetition is meaningful

Rule Details

• Rule ID: MDBOOK004
• Aliases: no-duplicate-chapter-titles
• Category: MdBook
• Severity: Warning
• Auto-fix: No

Impact

Duplicate titles can cause:

• Confusing navigation sidebar
• Ambiguous URL paths
• Search result confusion
• Poor user experience

Related Rules

• MD024 - No duplicate headings
• MDBOOK003 - SUMMARY.md structure
• MDBOOK025 - SUMMARY.md heading structure