Markdown Validator
Validate Markdown syntax and catch common issues like unclosed fences, broken links, and malformed tables — runs entirely in your browser.
Input Markdown
Validation Report
Markdown Validation Examples
Valid Markdown has proper spacing and closed fences. Examples:
Valid Markdown
Invalid – missing heading space and unclosed code fence
#API needs a space after #. The code block is missing closing ```.
Paste either example into the editor above. Use Sample to load more data.
What Is a Markdown Validator?
Markdown has syntax rules. Unclosed code fences, broken links, malformed tables, or invalid HTML can cause rendering issues. A Markdown validator checks your document and reports common problems. The CommonMark spec defines the syntax, and Markdown syntax reference by John Gruber is where it all started.
This tool parses your Markdown and generates a validation report. It runs entirely in your browser. Nothing is sent to a server. For formatting, use the Markdown Formatter. For linting (style rules), use the Markdown Linter.
How to Use This Tool
Paste or Upload Markdown
Copy your Markdown and paste it into the left editor. You can also click Upload to load a .md or .markdown file. The Sample button loads example data.
Check the Validation Report
The right panel shows the report. It lists issues like unclosed fences, broken reference links, malformed tables, or empty headings. Download the report for sharing.
Fix and Revalidate
Fix issues in the input and revalidate. For formatting, use the Markdown Formatter. For converting to HTML, use Markdown to HTML.
When Markdown Validation Helps
When publishing docs, READMEs, or content to GitHub, GitLab, or static sites like Jekyll and Hugo, validation catches issues before they cause broken rendering. The GFM spec defines tables and extensions. Unclosed code blocks or malformed tables can break entire pages. Running your Markdown through here gives you confidence before merge or deploy.
Content from multiple authors or AI-generated Markdown often has subtle errors. Validating here provides a checklist. For style consistency (e.g. heading levels, list formatting), use the Markdown Linter.
Frequently Asked Questions
What does Markdown validation check?
The validator checks for common Markdown issues: skipped heading levels (e.g. going from H1 to H3), unclosed fenced code blocks, malformed link syntax [text](url), inconsistent list indentation, and empty heading markers. It doesn't enforce a style guide — it checks for structural errors.
Does valid Markdown mean it will render correctly everywhere?
Not necessarily. Different Markdown parsers have different rules — a document valid in CommonMark may render differently in GitHub or Notion. Validation catches syntax errors but cannot guarantee visual consistency across all renderers.
Can I validate a README file?
Yes — paste the entire README.md content and the validator will check for structural issues. This is especially useful before committing to GitHub to catch formatting problems early.
Is there a size limit for validation?
No server-side limits — validation runs entirely in your browser. Typical README files and documentation pages validate instantly regardless of size.
Related Tools
Learn more: CommonMark, CommonMark spec, GitHub Flavored Markdown, Markdown Guide, GitHub, W3C HTML, GitLab, Hugo.