Does the Markdown linter fix or format my file?

No. It reports exact findings without rewriting the document. Some issues, such as duplicate headings and missing references, need author judgment and do not have a safe automatic fix.

No. The Markdown lint checker is available without an account.

Is my Markdown uploaded?

No. Pasted text and uploaded Markdown files are read and checked locally in your browser.

What are the input limits?

Paste Markdown or upload one .md or .markdown file no larger than 1 MB.

Markdown Lint Checker

Find Markdown style, structure, link, and spacing issues with line-level results.

This tool requires JavaScript. If you don't see the editor, enable JavaScript and reload.

How to use Markdown Lint Checker

1Paste Markdown into the editor or upload a .md or .markdown file up to 1 MB.
2Select “Lint Markdown” to run the same default rule configuration used by the mdedit editor.
3Review each severity, rule ID, line, column, and message.
4Fix the source where author judgment is needed, then run the lint check again.

Details

What this Markdown lint checker checks

The checker uses the same shared rule configuration as the mdedit editor. It checks ATX heading style, duplicate headings, list indentation and markers, emphasis markers, empty URLs, undefined references, link-title style, lines over 120 characters, and trailing spaces. Results preserve each rule ID, severity, line, and column.

Markdown linting versus formatting

Linting identifies where Markdown differs from the configured conventions; it does not rewrite the document automatically. That avoids unsafe changes to duplicate headings, missing references, and other findings that require author judgment. Use the line-level results as a formatting checklist, then run the checker again.

What the validator does not prove

A clean result means the enabled lint rules found no issues. It does not verify factual accuracy, external link destinations, accessibility, prose quality, every Markdown flavor, or syntax inside Mermaid blocks. Always preview the document in its publishing destination.

Private, browser-local Markdown checks

Pasted text and uploaded .md or .markdown files are read and checked in your browser without a server round trip. Inputs are limited to 1 MB so a very large document fails with a clear size message instead of freezing the page.

Example

Find a duplicate heading, an undefined reference, and a list-marker style issue with exact locations.

Input (Markdown)

# Release notes

## Changes

## Changes

See the [migration guide][missing].

* Added offline recovery

Lint findings

ERROR no-duplicate-headings — Line 5
ERROR no-undefined-references — Line 7
WARNING unordered-list-marker-style — Line 9

FAQ

Which Markdown lint rules run?: The tool checks heading style, duplicate headings, list indentation and markers, emphasis markers, empty URLs, undefined references, link-title style, 120-character lines, and trailing spaces with the editor default configuration.
Does the Markdown linter fix or format my file?: No. It reports exact findings without rewriting the document. Some issues, such as duplicate headings and missing references, need author judgment and do not have a safe automatic fix.
Do I need to log in?: No. The Markdown lint checker is available without an account.
Is my Markdown uploaded?: No. Pasted text and uploaded Markdown files are read and checked locally in your browser.
What are the input limits?: Paste Markdown or upload one .md or .markdown file no larger than 1 MB.