markdown-fast-py

Fast Markdown to HTML renderer — GFM tables, syntax highlighting, XSS-safe, extensible.

Pure Python. Zero dependencies. Production-ready.

Install

pip install markdown-fast-py

Quick Start

import markdown_fast_py as md

html = md.convert("# Hello\n\nThis is **bold** and _italic_.")
print(html)
# <h1 id="hello">Hello</h1>
# <p>This is <strong>bold</strong> and <em>italic</em>.</p>

Features

• CommonMark-compatible block and inline parsing
• GFM tables with per-column alignment
• Syntax highlighting for 15+ languages — pure Python, no external deps
• XSS sanitization — allowlist-based, strips event handlers and javascript: URIs
• Task lists (- [x] done / - [ ] todo)
• Strikethrough (~~text~~)
• Autolinks (bare URLs and <angle-bracket> style)
• Setext and ATX headings with automatic slug id attributes
• Blockquotes, fenced and indented code blocks
• Ordered and unordered lists with nesting
• Hard line breaks ( \n)
• Reference-style links and images
• Extension system: footnotes, math, anchors, TOC, definition lists
• Command-line tool (markdown-fast)

Usage

One-shot conversion

from markdown_fast_py import convert

html = convert(source)

Reusable instance

from markdown_fast_py import Markdown

md = Markdown(
    highlight_code=True,   # syntax-highlight fenced code blocks
    sanitize=True,         # strip dangerous HTML (XSS-safe)
    heading_ids=True,      # add id="slug" to headings
    safe_links=True,       # block javascript: URLs
    breaks=False,          # treat single newline as <br>
    xhtml=False,           # emit XHTML-style void elements
    table_class="",        # optional CSS class on <table>
    extensions=[],         # see Extensions section
)

html = md.render(source)
# or equivalently:
html = md.convert(source)
html = md(source)          # callable

API reference

convert(text, **options) -> str

One-shot Markdown-to-HTML conversion.

Parameter	Type	Default	Description
text	str	—	Markdown source
highlight_code	bool	True	Syntax-highlight fenced code blocks
sanitize	bool	True	XSS-sanitize the output
heading_ids	bool	True	Add id attributes to headings
safe_links	bool	True	Block javascript: / data: hrefs
breaks	bool	False	Newlines become <br>
xhtml	bool	False	Self-closing void elements
smart_quotes	bool	False	Curly quotes
table_class	str	""	CSS class on <table>
extensions	list	[]	Extensions to enable

sanitize(html) -> str

Standalone XSS sanitizer — works on HTML from any source.

from markdown_fast_py import sanitize

clean = sanitize('<a href="javascript:alert(1)">click</a>')
# <a href="#">click</a>

highlight(code, language) -> str

Standalone syntax highlighter returning HTML with hl-* CSS classes.

from markdown_fast_py import highlight

html = highlight("def foo(): pass", "python")

parse(text) -> Node

Low-level AST parser. Returns a Node tree you can traverse or transform.

from markdown_fast_py import parse, NodeType

doc = parse("# Hello\n\n- item")
for child in doc.children:
    print(child.type, child.level if child.type == NodeType.HEADING else "")

Syntax Highlighting

Fenced code blocks are highlighted when a language tag is provided:

```python
def hello(name: str) -> str:
    return f"Hello, {name}!"
```

Supported languages

Language	Tags
Python	python, py
JavaScript	javascript, js, jsx
TypeScript	typescript, ts, tsx
HTML/XML	html, xml
CSS/SCSS	css, scss, sass
JSON	json
SQL	sql
Bash/Shell	bash, sh, shell, zsh
Go	go, golang
Rust	rust, rs
YAML	yaml, yml
Diff	diff, patch

The highlighter emits <span class="hl-*"> markup. Include the bundled theme or write your own CSS:

from markdown_fast_py import CSS_THEME_DARK, CSS_THEME_LIGHT

# Embed in a <style> tag:
print(f"<style>{CSS_THEME_DARK}</style>")

XSS Sanitization

The sanitizer uses a strict allowlist of safe tags and attributes. Event handlers (onclick, onload, …), <script>, <iframe>, and javascript: / data: URIs are stripped automatically.

dangerous = '<p onclick="steal()">Hi <script>alert(1)</script></p>'
safe = convert(dangerous)
# <p>Hi </p>

Extensions

Enable built-in extensions by name or instance:

md = Markdown(extensions=["footnotes", "anchors", "toc"])

Available extensions

Name	Class	Description
footnotes	FootnotesExtension	[^1] references and definitions
math	MathExtension	$inline$ and $$block$$ pass-through for MathJax/KaTeX
anchors	AnchorExtension	Self-link ¶ on every heading
toc	TableOfContentsExtension	Replace [TOC] with a nested <nav>
deflist	DefinitionListExtension	term\n: definition → <dl>

Custom extensions

from markdown_fast_py import Extension, Markdown

class MyExtension(Extension):
    name = "mine"

    def preprocess(self, text: str) -> str:
        return text.replace(":rocket:", "🚀")

    def postprocess_html(self, html: str) -> str:
        return html.replace("TODO", '<mark>TODO</mark>')

md = Markdown(extensions=[MyExtension()])

GFM Tables

| Name    | Age | City      |
|---------|:---:|----------:|
| Alice   | 30  | New York  |
| Bob     | 25  | London    |

Column alignment: :--- left, ---: right, :---: centre.

Command Line

# Convert from stdin
echo "# Hello" | markdown-fast

# Convert a file
markdown-fast README.md

# Output a full HTML page with dark theme
markdown-fast --page --theme dark --title "Docs" README.md > docs.html

# Disable highlighting and sanitization
markdown-fast --no-highlight --no-sanitize input.md

# Enable extensions
markdown-fast --extensions anchors toc footnotes README.md

usage: markdown-fast [-h] [-o FILE] [--no-highlight] [--no-sanitize]
                     [--no-heading-ids] [--breaks] [--xhtml]
                     [--page] [--title TITLE] [--theme {dark,light,none}]
                     [--extensions [EXT ...]] [--version]
                     [FILE]

License

MIT © Vladyslav Zaiets