Markdown Lint - Online Validator
Check Markdown against the markdownlint rule set and fix problems automatically — all in your browser.
Problems
Loading the markdownlint rules…
What Is markdownlint?
markdownlint is the de facto standard style checker for Markdown, created by David Anson. It defines roughly fifty rules (MD001–MD059) covering heading structure, list consistency, blank lines, trailing whitespace, code fences, link syntax, and more. Each rule has an ID like MD009 and an alias like no-trailing-spaces, and every finding here links to the official rule documentation.
This page runs the same rule engine that powers the VS Code markdownlint extension and the markdownlint-cli tools used in CI pipelines. If your document passes here, it will pass the default configuration in your editor and your build — handy for fixing a README before a pull request without installing anything.
How Auto-Fix Works
Many rules carry machine-applicable fixes: trailing spaces are trimmed, multiple blank lines collapsed, list markers and heading spacing normalized, and a final newline added. The Fix automaticallybutton applies every available fix at once using markdownlint's own applyFixes helper, then re-lints the result. Findings without a fix — like a skipped heading level — stay in the list for manual review.
The line-length rule (MD013) is off by default because prose lines longer than 80 characters are a stylistic choice; enable the checkbox if your project enforces it. Your text never leaves the browser.
Frequently Asked Questions
Which rules are checked?
The standard markdownlint rule set used by the VS Code extension and CI tools: heading structure, list consistency, spacing, trailing whitespace, link syntax, and more. Each finding links to the rule documentation.
Can it fix the problems automatically?
Yes. The Fix button applies markdownlint's automatic fixes for every fixable rule, such as trailing spaces, heading spacing, and list markers. Unfixable findings remain listed for manual review.