What formatting problems does the auto-fix handle?

Powered by markdownlint rules, it automatically fixes: ① Missing space after # in headings (##Heading → ## Heading) ② Missing blank lines around headings ③ Trailing whitespace on lines ④ Ordered lists where every item is "1." — converted to incrementing 1. 2. 3. (note: markdownlint allows all-ones by default; this tool explicitly enables the ordered-numbering check) ⑤ Incorrect spacing after list markers ⑥ Missing newline at end of file ⑦ Hard tabs converted to spaces. All changes are format-only and never alter content.

What issues can't be auto-fixed?

Some issues require human judgment and won't be touched automatically: line length (reasonable long lines depend on context), whether links resolve correctly, whether code-block language tags are accurate, or whether image alt text is meaningful. For a full lint report, pair this with markdownlint-cli2 locally.

Is my Markdown content uploaded to a server?

No. Format checking and auto-fixing run entirely in your browser using the markdownlint JavaScript library. Your Markdown never leaves your device — safe for internal documents and unpublished drafts.

Will the fix break my content?

No content words are ever changed — only whitespace, blank lines, and indentation are adjusted. That said, we recommend downloading a backup first, or using Ctrl/Cmd + Z in the editor to review the diff after fixing.

How is this different from Prettier's Markdown formatting?

Prettier re-flows the entire document (line width, quotes, spacing) — it's aggressive and suited to enforcing consistency across a team codebase. This tool uses markdownlint and only fixes clear rule violations, making far fewer changes. It's better suited for the "fix someone else's poorly formatted .md file" scenario without rewriting your prose.

Markdown Format Checker & Auto-Fix · Fix Markdown Errors Online

Paste or import Markdown and auto-fix formatting issues — output a clean, standards-compliant .md file.

Import file

What You Can Do With It?

Check Doc Formatting

Automatically catch heading level errors, missing spaces, and other Markdown issues

Validate Before PR Merge

Run lint checks on Markdown docs before merging pull requests

Enforce Team Style

Configure shared rules to keep writing style consistent across contributors

Auto-Fix Issues

Automatically fix correctable formatting problems after scanning

Clean Up Legacy Docs

Batch-check and fix formatting in old documents to improve doc quality

Learn Markdown Best Practices

Lint hints teach standard Markdown conventions and build good writing habits

Why Choose This Tool?

One-click auto-fix

Heading spaces, list indentation, trailing spaces, missing blank lines — all corrected automatically

Detailed error list

Issues listed by line number with click-to-jump navigation — fix progress at a glance

Content stays local

Linting and fixing run entirely in the browser — your document never leaves the device

markdownlint-compatible

Uses the standard markdownlint rule set — consistent with VSCode plugins and CI lint checks

How To Use?

Input Markdown

Paste or upload the Markdown document you want to check

Run Lint Check

Scan for formatting issues with locations and fix suggestions listed

Fix & Export

Auto-fix correctable issues and download the cleaned-up document

Input Markdown

Paste or upload the Markdown document you want to check

Run Lint Check

Scan for formatting issues with locations and fix suggestions listed

Fix & Export

Auto-fix correctable issues and download the cleaned-up document

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Online LaTeX formula editor with real-time preview. Insert Greek letters, integrals, matrices with one click. Export to SVG/PNG. Runs entirely in browser — no data upload.

Markdown Share

Paste your Markdown document and generate a shareable preview link. Recipients see the full rendered layout without installing anything. Links expire automatically after 7 days. Data stays in your browser.

HTML to MD

Paste any HTML — copied from a webpage, WeChat article, blog post or rich-text editor — and convert it to clean, GFM-flavored Markdown. Smart cleanup of inline styles, tables, code blocks, blockquotes and images. Runs 100% in your browser; nothing is uploaded.

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For Markdown writers who already draft in Obsidian, VSCode, or Typora: paste your .md, see a true WeChat-style live preview, copy and paste into the WeChat editor with all formatting preserved. Supports local image uploads: images referenced in your Markdown are detected automatically, uploaded and stored in browser IndexedDB (persists across page reloads), or import a ZIP / folder to batch-import images. Code highlighting, blockquotes, tables — all rendered the way WeChat displays them.

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Frequently Asked Questions

: Powered by markdownlint rules, it automatically fixes: ① Missing space after # in headings (##Heading → ## Heading) ② Missing blank lines around headings ③ Trailing whitespace on lines ④ Ordered lists where every item is "1." — converted to incrementing 1. 2. 3. (note: markdownlint allows all-ones by default; this tool explicitly enables the ordered-numbering check) ⑤ Incorrect spacing after list markers ⑥ Missing newline at end of file ⑦ Hard tabs converted to spaces. All changes are format-only and never alter content.
: Some issues require human judgment and won't be touched automatically: line length (reasonable long lines depend on context), whether links resolve correctly, whether code-block language tags are accurate, or whether image alt text is meaningful. For a full lint report, pair this with markdownlint-cli2 locally.
: No. Format checking and auto-fixing run entirely in your browser using the markdownlint JavaScript library. Your Markdown never leaves your device — safe for internal documents and unpublished drafts.
: No content words are ever changed — only whitespace, blank lines, and indentation are adjusted. That said, we recommend downloading a backup first, or using Ctrl/Cmd + Z in the editor to review the diff after fixing.
: Prettier re-flows the entire document (line width, quotes, spacing) — it's aggressive and suited to enforcing consistency across a team codebase. This tool uses markdownlint and only fixes clear rule violations, making far fewer changes. It's better suited for the "fix someone else's poorly formatted .md file" scenario without rewriting your prose.

Encountered other problems or suggestions? Have a bug or suggestion? Drop us an email.

Email Us

Why Markdown formatting standards matter

Markdown's strength is expressing structure in plain text — but that same simplicity creates a blind spot: different tools have wildly different tolerance for "sloppy" formatting. GitHub will render ##Heading (no space after #) as plain text; markdownlint, Vale, and CI pipelines flag trailing spaces as lint errors; pandoc collapses heading hierarchy when blank lines are missing.

These issues seem trivial at the source but cascade badly in team collaboration, version control, and multi-platform publishing: meaningless whitespace diffs in PRs, CI format checks blocking releases, the same .md rendering inconsistently across renderers. Fixing the format upfront is a form of respect — for your own drafts, and for every downstream tool in your pipeline.

MeTool's Markdown Format Checker & Auto-Fix tool is powered by the industry-standard markdownlint ruleset and runs entirely in your browser — content never leaves your device, making it safe for internal docs and unpublished drafts.

7 common formatting problems the auto-fix handles

① Missing space after # in headings (MD018 / MD019)

Many people habitually write ##Heading. Browser previews often let it slide, but strict renderers treat it as plain text. Auto-fix inserts the required space: ## Heading.

② Missing blank lines around headings (MD022)

A heading that immediately follows body text without a blank line causes some renderers and export tools to "glue" the heading to the paragraph above, breaking hierarchy. Auto-fix inserts a blank line before and after each heading.

③ Trailing whitespace (MD009)

Trailing spaces have special meaning in Markdown (two spaces = forced line break), but unintentional trailing spaces create Git diff noise and CI lint failures. Auto-fix removes them.

④ Inconsistent ordered-list numbering (MD029)

Copy-paste scenarios and certain editors output 1. 1. 1. throughout. GitHub renders it fine, but Word and PDF export tools may get confused. Auto-fix normalises the sequence to 1. 2. 3..

⑤ Incorrect spacing after list markers (MD030)

Spec requires exactly one space after - or *. Some tools produce two or zero. Auto-fix standardises to a single space.

⑥ Missing newline at end of file (MD047)

POSIX requires text files to end with a newline. Without one, Git shows "No newline at end of file", generating spurious diffs in collaborative projects.

⑦ Hard tabs (MD010)

Literal tab characters outside code blocks render at inconsistent widths across renderers. Auto-fix converts them to four spaces (the Markdown indentation standard).

Auto-fix vs. Prettier: which one to reach for

The two tools have different jobs:

This tool (markdownlint auto-fix): fixes clear rule violations only, never rewrites prose. Best for "clean up the messy .md someone sent me" — minimal diffs, no risk of accidentally re-flowing your text.
Prettier: a style enforcer that re-lays out the entire document — line width (default 80 chars), punctuation spacing, list indentation all get reset. Great for enforcing consistency across a team codebase via CI, but too aggressive for "just fix a few lint errors".

Recommended workflow: run this tool to fix format errors → polish content in the Markdown editor → publish to WeChat or export to PDF.

Automating format checks in CI / pre-commit hooks

This tool is designed for the manual "fix one .md right now" scenario. If you maintain a Markdown documentation library or docs site, consider pairing it with these automation approaches:

markdownlint-cli2: run markdownlint-cli2 "**/*.md" locally or in CI; add --fix to auto-repair fixable issues, and let a non-zero exit code block the pipeline.
Pre-commit hook: combine husky + lint-staged to auto-run markdownlint --fix on changed .md files before every commit, so only clean commits land in the repo.
GitHub Actions: add a markdownlint-cli2 step to PR workflows, making format compliance a merge gate.

All of these use the same ruleset as this browser tool — fixes produced here will match exactly what the CLI produces.