# MD066 - Footnote validation
Aliases: `footnote-validation`
## What this rule does
Checks that all footnote references have corresponding definitions and vice versa.
## Why this matters
- **Prevents broken footnotes**: References without definitions leave readers confused
- **Avoids clutter**: Unused definitions add noise to your document
- **Ensures completeness**: All footnotes work as intended
- **Improves accessibility**: Screen readers can follow properly linked footnotes
## Examples
### Correct
```markdown
This text has a footnote[^1] that is properly defined.
Another reference[^note] works too.
```
### Incorrect - orphaned reference
```markdown
This references[^missing] a footnote that doesn't exist.
```
**Warning**: `Footnote reference [^missing] has no corresponding definition`
### Incorrect - orphaned definition
```markdown
Some text without any footnote references.
```
**Warning**: `Footnote definition [^unused] is never referenced`
## Configuration
This rule has no configuration options.
## Automatic fixes
This rule cannot automatically fix issues because:
- Missing definitions require you to provide the footnote content
- Unused definitions might be intentional placeholders or copy-paste errors
## Footnote syntax
Footnotes are a common markdown extension (not part of CommonMark):
- **Reference**: `[^identifier]` placed inline in text
- **Definition**: `[^identifier]: content` at the start of a line
Footnote definitions can span multiple lines with indentation:
```markdown
```
## Related rules
- [MD067 - Footnote definition order](md067.md)
- [MD068 - Empty footnote definitions](md068.md)