Markdown Formatter

Normalize full-width→half-width, fix spacing. HackMD-compatible.

Data is never sent to the server. Everything runs locally in your browser. Safe for sensitive information.

About this tool

This tool formats Markdown in one click. Three features: 1) Normalize full-width # to half-width, ##text to ## text, 2) Fix header and list spacing, 3) Preserves code blocks. HackMD-compatible. No data sent to server.

Tool interface

Input
Formatted

Formatting rules

  • Full→half: ＃→#, －→-, ０-９→0-9, ［］→[], （）→() etc.
  • Headers: ##text → ## text
  • Lists: -item → - item, 1.item → 1. item
  • Blockquotes: >text → > text, さらに> 引用 → さらに > 引用
  • List indent: Leading full-width space → 2 half-width spaces
  • :::details: Add space between :::details and title
  • Tables: |a|b| → | a | b |
  • Footnotes: [^1]:content → [^1]: content
  • Horizontal rules: *** / ___ → ---
  • Zenn image: ![](url=250x) → ![](url =250x)
  • Preserved: Code blocks, math ($$/$...$), \*...\*/\[...\], links/images, :::message/:::details/:::note, <details>/<!-- -->/@[card] etc.
  • In-text #: Only heading # at line start is half-width; mid-sentence # preserved

Supported Services

Compatible with Markdown syntax used by the following services. Also works with many others (GitHub, GitLab, HackMD, Obsidian, etc.).

Zenn ▼

Supported syntax:

  • Headings, lists, blockquotes, tables, footnotes, horizontal rules
  • Images: ![](url =250x) width, caption *text*
  • Code: lang:filename, diff js
  • Math: $$ block, $ inline (KaTeX)
  • Custom: :::message / :::message alert / :::details (nest with :::)
  • Embeds: @[card] @[tweet] @[youtube] @[gist] etc.
  • mermaid, emoji :emoji:, HTML comment <!-- -->
Qiita ▼

Supported syntax:

  • GFM + extensions. Code: lang:filename, diff_lang
  • :::note info / warn / alert
  • <details><summary> collapsible
  • Checkbox - [ ] - [x], description list <dl>
  • Math: ```math or $`...`$
  • PlantUML, Mermaid, emoji, link cards (URL-only line)
  • Reference links [text][ref], anchor #heading
note ▼

Supported syntax:

  • Headings, blockquotes, lists, emphasis, code blocks, strikethrough, horizontal rules
  • Headings: h2, h3 only (h1→h2)
  • Emphasis: ** preferred (__ needs spaces)
  • Lists: avoid mixing - and *
VSCode / GFM ▼

Supported syntax:

  • Headings, lists, blockquotes, links, images, tables, horizontal rules
  • Code: lang:filename (e.g. c:main.c)
  • Italic *, bold **, strikethrough ~~
Zenn Qiita note Qiita (Markdown Guide)

Zenn, Qiita, note, HackMD, GitHub, GFM and more.

Usage

  1. Paste Markdown in the input field
  2. Click Format for full-width→half-width and spacing fix
  3. Code blocks preserved. HackMD-compatible output

When to use

Fix messy Markdown from copy-paste, format before using in HackMD.

Examples

#heading→# heading, ##text→## text, -item→- item

FAQ

What is Markdown?

Lightweight markup for headers, lists, links. Supported by GitHub, Notion, HackMD.

How to write Markdown headers?

# for h1, ## for h2, ### for h3. Space after # required. Full-width # is not recognized.

Full-width vs half-width?

Full-width = Japanese input width (#, space). Half-width = alphanumeric (#, space). Markdown needs half-width.

How to write code blocks in Markdown?

Wrap with ``` or 4 spaces at line start. Add language after ``` for highlighting. This tool preserves code blocks.

Is Markdown Formatter free?

Free to use, no sign-up required.

Is data sent to a server?

Input is processed locally in your browser—nothing is sent to our servers.

Supported browsers?

Tested on recent Chrome, Edge, Firefox, and Safari.

Offline use?

Core features work offline after the first load.

vs CLI or desktop apps?

Markdown Formatter is an install-free online alternative to CLI or desktop apps.

When to use it?

Use it when: Fix messy Markdown from copy-paste, format before using in HackMD.

Usage example?

Example: #heading→# heading, ##text→## text, -item→- item

Main features?

Full-width→half-width conversion, Header and list spacing fix, HackMD-compatible

How is this different from similar tools?

Markdown Formatter runs in the browser with no install—ideal for quick checks before heavier CLI or IDE workflows.

Search keywords

Markdown Formatter

Basic workflow

  1. Paste Markdown in the input field
  2. Click Format for full-width→half-width and spacing fix
  3. Code blocks preserved. HackMD-compatible output

Practical use cases

  • Fix messy Markdown from copy-paste, format before using in HackMD.
  • This tool formats Markdown in one click. Three features: 1) Normalize full-width # to half-width, ##text to ## text, 2) Fix header and list spacing, 3) Preserves code blocks. HackMD-compatible. No data sent to server.
  • Full-width→half-width conversion
  • Header and list spacing fix

Privacy & data handling

Input is processed locally in your browser—nothing is sent to our servers.

Things to watch out for

  • Treat Markdown Formatter as a quick check — re-verify critical values in your editor or CI before shipping.
  • This tool runs locally: closing the tab clears unsaved input. Copy results you need to keep.
  • Very large pastes can freeze a tab briefly — wait for the result before closing the tab.

Related learning content

Related tools

Tool set

Temporary Share & Memo Set