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Markdown Checker Online

Paste your Markdown and run a quick lint-style check for common formatting and structure problems (headings, links, code fences, references, and whitespace). This tool runs locally in your browser—no uploads.

Category: Text · URL: /tools/markdown-checker-online.html

Markdown input

Report

Run a check to see results.

Note: This checks Markdown structure and syntax patterns only. It does not fetch URLs to verify whether links are reachable.

Related tools

Markdown Checker — Find Broken Links, Headings, and Code Fences Markdown Formatter (VS Code-Friendly) Markdown Formatter Online Markdown File Generator Text Formatter Online
Privacy: runs locally in your browser. No uploads, no tracking scripts.

How to use

Use this checker to catch common Markdown issues before publishing or committing.

  1. Paste your Markdown into the input box.
  2. Choose which checks to run (headings, links, code fences, whitespace).
  3. Click Check Markdown to generate a compact report.
  4. Fix issues and re-run until the report is clean.
Keywords this page targets (natural cluster): markdown checker online, check markdown syntax online, markdown lint online, validate markdown, markdown link syntax checker, markdown reference link checker, unclosed code fence checker, markdown heading checker, duplicate heading checker, markdown heading level jump, markdown trailing whitespace checker, markdown tab character checker, markdown line length checker, markdown image alt text checker, gfm markdown checker, markdown report generator, markdown quality check, markdown validator for github, find markdown errors, markdown links validator, markdown formatting checker, markdown static analysis tool
Secondary intents covered: Find unclosed ``` code fences and mismatched fence markers, Detect heading level jumps (e.g., H2 → H4) and missing heading text, Flag duplicate headings that may create duplicate anchors in renderers, Spot malformed inline links/images like [text](url and ](url), Identify missing reference link definitions ([id]: url) used in the document, Clean up trailing whitespace, tabs, and overlong lines before committing

FAQ

Does this tool check if URLs are actually reachable (true broken links)?

No—this is a syntax/structure checker. It flags malformed link Markdown and missing reference definitions, but it doesn’t fetch URLs.

Is my Markdown uploaded to a server?

No. The checks run locally in your browser and the tool does not make network requests.

What Markdown flavor does it support?

It targets common Markdown and GitHub-flavored patterns (headings, fenced code blocks, inline links/images, and reference links).

How does it detect duplicate headings?

It generates a simple slug from heading text and warns when the same slug appears more than once.

What counts as a code fence issue?

It reports unclosed fenced blocks (``` or ~~~) and only closes fences that match the same marker character.

Why does it warn about heading level jumps?

Large jumps (like H2 to H4) often break document structure and table-of-contents output, so they’re flagged as warnings.

Can I change the maximum line length rule?

Yes—set the Max line value to match your style guide (for example 80, 100, or 120).