markdownlint/doc/md025.md

# `MD025` - Multiple top-level headings in the same document

Tags: `headers`, `headings`

Aliases: `single-h1`, `single-title`

Parameters:

* `front_matter_title`: RegExp for matching title in front matter (`string`, default `^\s*title\s*[:=]`)
* `level`: Heading level (`integer`, default `1`)

This rule is triggered when a top-level heading is in use (the first line of
the file is an h1 heading), and more than one h1 heading is in use in the
document:

```markdown
# Top level heading

# Another top-level heading
```

To fix, structure your document so there is a single h1 heading that is
the title for the document. Subsequent headings must be
lower-level headings (h2, h3, etc.):

```markdown
# Title

## Heading

## Another heading
```

Note: The `level` parameter can be used to change the top-level (ex: to h2) in
cases where an h1 is added externally.

If [YAML](https://en.wikipedia.org/wiki/YAML) front matter is present and contains
a `title` property (commonly used with blog posts), this rule treats that as a top
level heading and will report a violation for any subsequent top-level headings.
To use a different property name in the front matter, specify the text of a regular
expression via the `front_matter_title` parameter. To disable the use of front
matter by this rule, specify `""` for `front_matter_title`.

Rationale: A top-level heading is an h1 on the first line of the file, and
serves as the title for the document. If this convention is in use, then there
can not be more than one title for the document, and the entire document
should be contained within this heading.