Markdown ↔ HTML Converter

Markdown variants: more than one standard

Markdown was created by John Gruber in 2004 as a way to write HTML using simpler syntax. The original spec was minimal and ambiguous in many corner cases, which led to incompatible variants: CommonMark (the most formal spec, used by Stack Overflow), GitHub Flavored Markdown (CommonMark plus tables, task lists, strikethrough, autolinks), Reddit's variant (no tables, custom syntax for spoilers), and dozens of others.

This tool uses GitHub Flavored Markdown by default — the variant most developers actually write. Tables, fenced code blocks with language hints, task lists with - [x], strikethrough with ~~text~~, and automatic URL linking all work.

GFM features worth knowing

### Tables (pipes + alignment)
| Column A | Column B | Column C |
|----------|:--------:|---------:|
| left     |  center  |    right |

### Task lists
- [x] done thing
- [ ] todo thing

### Fenced code with language
```js
const greet = name => 'hello ' + name;
```

### Strikethrough
~~struck through~~

### Autolink
https://example.com works without [text](url)

Going the other direction: HTML → Markdown

Converting HTML back to Markdown is "lossy" because HTML can express things Markdown can't (style attributes, classes, custom elements, nested structures). This tool uses Turndown — it preserves the structure Markdown supports (headings, paragraphs, lists, links, images, code, blockquotes, emphasis) and drops everything else.

Use cases: extracting documentation from a website, converting rich-text editor output to plain Markdown for storage, normalizing HTML pasted from various sources into a consistent format.

What this tool doesn't do

• Render rich previews of GitHub-specific features like alerts (> [!NOTE]), mermaid diagrams, or footnote backreferences. The conversion produces correct HTML; the visual rendering on GitHub.com adds custom CSS we don't replicate here.
• Sanitize HTML for safety. If you're rendering user-submitted Markdown on a site, you MUST run the HTML output through a sanitizer like DOMPurify before inserting it into the page. marked by itself accepts inline HTML, which is an XSS vector.
• Preserve semantic HTML on round-trips. Convert HTML → Markdown → HTML and you may get different (but visually equivalent) markup. <strong> may become <b>, attributes may be lost.