Markdown Formatter
Normalize full-width→half-width, fix spacing. HackMD-compatible.
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
:::detailsand title - Tables:
|a|b|→| a | b | - Footnotes:
[^1]:content→[^1]: content - Horizontal rules:
***/___→--- - Zenn image:
→ - 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:
width, caption*text* - Code:
lang:filename,diff js - Math:
$$block,$inline (KaTeX) - Custom:
:::message/:::message alert/:::details(nest with:::) - Embeds:
@[card]@[tweet]@[youtube]@[gist]etc. - mermaid, emoji
:emoji:, HTML comment<!-- -->
Qiita ▼
Supported syntax:
- GFM + extensions. Code:
lang:filename,diff_lang :::note info/warn/alert<details><summary>collapsible- Checkbox
- [ ]- [x], description list<dl> - Math:
```mathor$`...`$ - 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, HackMD, GitHub, GFM and more.
Usage
- Paste Markdown in the input field
- Click Format for full-width→half-width and spacing fix
- 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?
Data stays on your device; we do not store it on 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, 整形, 見出し, HackMD, 表変換
Basic workflow
- Paste Markdown in the input field
- Click Format for full-width→half-width and spacing fix
- 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
Data stays on your device; we do not store it on our servers.
Things to watch out for
- Always double-check before pasting output into production
- Try incognito if extensions break the page
- Wait for processing on large inputs