Markdown Validator - Free Online Markdown Lint Tool (markdownlint)

What is a Markdown Validator?

A Markdown validator (also called a Markdown linter) analyzes your Markdown source and reports violations of style and correctness rules — skipped heading levels, inconsistent list markers, trailing whitespace, hard tabs, bare URLs, code fences without a language, and dozens more. Clean, consistent Markdown renders predictably on GitHub, in static-site generators, and in converters, and it keeps documentation diffs easy to review.

This tool embeds markdownlint, the de-facto standard Markdown lint engine for Node.js, running entirely in your browser. It applies the same default rule set (MD001–MD059) used by markdownlint-cli2, the VS Code markdownlint extension, and countless CI pipelines — so what passes here passes there. The Fix issues button applies the library’s automatic fixes, mirroring markdownlint-cli2 --fix.

How to Validate Markdown Online in 3 Steps

No installation, no account — just start typing.

1

Type or Paste Markdown

Write in the editor on the left, or paste an existing .md document such as a GitHub README.

2

Review the Issues

Lint results appear live with line numbers, rule IDs and doc links. Click an issue to jump to its line.

3

Fix Automatically

One click fixes every auto-fixable issue — the same behavior as markdownlint-cli2 --fix.

Why Use Our Markdown Lint Tool?

The trusted markdownlint engine, wrapped in a fast browser tool.

50+ markdownlint Rules

The complete default rule set (MD001-MD059) used by markdownlint-cli2 and the VS Code extension.

Lints as You Type

Issues update live with line numbers, rule IDs, and links to the official rule documentation.

One-Click Auto-Fix

Fix trailing spaces, list markers, blank lines and more automatically - like markdownlint-cli2 --fix.

In-Editor Markers

Problem lines are flagged in the Ace editor gutter; click any issue to jump straight to it.

100% Private

Linting runs entirely in your browser with the official markdownlint library. Nothing is uploaded.

CI-Consistent Results

Matches what markdownlint reports in GitHub Actions and CI pipelines with default settings.

Common markdownlint Rules Checked

A selection of the 50+ rules this validator applies. Every rule ID links to the official documentation.

Headings

MD001
heading-increment Heading levels should only increment by one level at a time
MD018
no-missing-space-atx No space after hash on ATX style heading
MD022
blanks-around-headings Headings should be surrounded by blank lines
MD025
single-h1 Multiple top-level headings in the same document
MD026
no-trailing-punctuation Trailing punctuation in heading
MD041
first-line-heading First line in a file should be a top-level heading

Lists

MD004
ul-style Unordered list style should be consistent
MD005
list-indent Inconsistent indentation for list items at the same level
MD007
ul-indent Unordered list indentation
MD029
ol-prefix Ordered list item prefix
MD030
list-marker-space Spaces after list markers
MD032
blanks-around-lists Lists should be surrounded by blank lines

Whitespace

MD009
no-trailing-spaces Trailing spaces
MD010
no-hard-tabs Hard tabs
MD012
no-multiple-blanks Multiple consecutive blank lines
MD013
line-length Line length should not exceed 80 characters
MD047
single-trailing-newline Files should end with a single newline character

Code, Links & More

MD031
blanks-around-fences Fenced code blocks should be surrounded by blank lines
MD034
no-bare-urls Bare URL used instead of a link
MD040
fenced-code-language Fenced code blocks should have a language specified
MD042
no-empty-links No empty links
MD045
no-alt-text Images should have alternate text (alt text)
MD058
blanks-around-tables Tables should be surrounded by blank lines

Frequently Asked Questions

Everything you need to know about the online Markdown validator.

What is a Markdown validator?

A Markdown validator (or Markdown linter) checks your Markdown source against a set of style and correctness rules, flagging problems like skipped heading levels, inconsistent list markers, trailing spaces, hard tabs, and missing code-block languages. This tool runs the same rule engine as the popular markdownlint library.

Which rules does this Markdown lint tool check?

It runs the full default markdownlint rule set - over 50 rules identified as MD001 through MD059 - covering heading structure, list formatting, whitespace, code blocks, links, images, and tables. Each result links to the official rule documentation.

Can it fix Markdown issues automatically?

Yes. Click the Fix button to automatically resolve every fixable issue, such as trailing spaces, missing blank lines around headings, bare URLs, and inconsistent list markers - the same behavior as the --fix option of markdownlint-cli2.

Is my Markdown uploaded to a server?

No. Validation runs entirely in your browser using the official markdownlint JavaScript library. Your text never leaves your device, so it is safe for private or confidential documents.

Is this the same as markdownlint and markdownlint-cli2?

This tool embeds the same markdownlint rule engine that powers markdownlint-cli2, the VS Code markdownlint extension, and thousands of CI pipelines - so the results match what those tools report with their default configuration.

Why should I lint my Markdown files?

Consistent Markdown renders more predictably across GitHub, documentation generators, and converters, and it keeps diffs clean in code review. Linting catches subtle issues - like a skipped heading level or a missing blank line - that can silently break rendering.

Is this Markdown validator free?

Yes, completely free with no sign-up and no limits. You can validate as many documents as you like.

Markdown Clean? Preview It or Ship It as PDF

See your validated Markdown rendered live, or convert it to a professionally formatted PDF in seconds — free and without watermarks.

Live Markdown Preview

Markdown Validator Free Online Markdown Lint Tool