What is it?
The Markdown Checker makes README files, documentation and blog posts look right in every app. It follows common markdownlint rules: heading levels that skip, more than one H1, “#Title” without a space, empty or reversed links, reference links that are never defined, images without alt text, code blocks that are never closed or have no language, bare web addresses, mixed list markers, tabs and stray trailing spaces.
Who is it for?
Developers writing GitHub READMEs, technical writers, bloggers who write in Markdown, and students preparing project reports.
How to use it
- Paste your code into the Markdown to check box, or tap Try a sample to see how it works.
- The list of problems updates as you type: ✕ marks an error, ! a warning. The line above it sums up, for example “2 errors, 1 warning. Tap Show to jump to the line.”
- Tap Show next to a problem to jump to that line, fix it, and watch the list update. Problems that are not on one line say Whole file. Clear empties the box.
Worked example
#My Project ### Install See https://example.com
Three messages appear: no space after # on line 1, a skipped heading level on line 2 (H1 to H3), and a bare link on line 3. The fixed version is # My Project, ## Install and See <https://example.com>.
Exactly two spaces at the end of a line make a line break; use a blank line for a new paragraph.
Errors and how to fix them
- “✓ No problems found”: the file follows the rules.
- No space after #: GitHub and most apps only treat “# Title” as a heading; “#Title” shows a hash in front.
- Heading level skipped: go from ## to ###, not straight to ####.
- More than one H1: keep a single # title; use ## for sections.
- “Mixed list markers: use … for the whole list”: pick - or * and use it for every item.
- Code block not closed or without a language: end it with ``` and start it with, for example, ```js.
- Bare link: write <https://…> or [text](https://…), which works everywhere.
Open the tool: Markdown Checker
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.