ฅᨐฅ Patitas

A Python Markdown parser and CommonMark parser for typed ASTs, frontmatter, directives, and notebook content.

from patitas import Markdown

md = Markdown()
html = md("# Hello **World**")

What is Patitas?

Patitas is a pure-Python Markdown parser that parses to a typed AST and renders to HTML. It's CommonMark 0.31.2 compliant, has a single runtime dependency (PyYAML, used for frontmatter), and is built for Python 3.14+.

Why people pick it:

• ReDoS-resistant — hand-written FSM lexer, no regex backtracking; a bounded nesting depth guards against stack exhaustion on adversarial input. See security for the current threat model.
• Typed AST — Frozen dataclasses (Heading, Paragraph, Strong, etc.) with IDE autocomplete and type checking.
• CommonMark — Full 0.31.2 spec compliance (652 examples).
• Incremental parsing — Re-parse only changed blocks; ~170x faster for small edits than full re-parse (up to ~430x for edits near the start of a document).
• Free-threading native — Frozen AST, ContextVar config, no shared mutable parser state. Parallel speedups vary by Python build, hardware, and corpus.
• LLM-safe — render_llm + composable sanitize policies for RAG, retrieval, safe context.
• Directives — MyST-style blocks (admonition, dropdown, tabs) plus custom directives.
• Notebook + frontmatter support — Parse .ipynb content and YAML frontmatter as part of content pipelines.

Use Patitas For

• Markdown to HTML pipelines — Render docs, blogs, and site content from Python
• Typed Markdown processing — Analyze or transform documents through a typed AST
• Secure user-input parsing — Handle untrusted Markdown without regex backtracking risk
• Content tooling — Frontmatter extraction, excerpts, meta descriptions, and notebook conversion
• Modern docs stacks — Directives, syntax highlighting, LLM-safe rendering, and incremental parsing

What it does

The public compatibility boundary is the top-level patitas package. Prefer from patitas import ... for integrations; direct imports from parser, lexer, and renderer implementation modules are still pre-1.0 internals unless the API reference says otherwise.

More Features

• ReDoS-resistant — hand-written FSM lexer, no regex backtracking; a bounded nesting depth guards against stack exhaustion on adversarial input. See security for the current threat model.
• Typed AST — Frozen dataclasses (Heading, Paragraph, Strong, etc.) with IDE autocomplete and type checking.
• CommonMark — Full 0.31.2 spec compliance (652 examples).
• Incremental parsing — Re-parse only changed blocks; ~170x faster for small edits than full re-parse (up to ~430x for edits near the start of a document).
• Free-threading native — Frozen AST, ContextVar config, no shared mutable parser state. Parallel speedups vary by Python build, hardware, and corpus.
• LLM-safe — render_llm + composable sanitize policies for RAG, retrieval, safe context.
• Directives — MyST-style blocks (admonition, dropdown, tabs) plus custom directives.
• Plugins — Tables, footnotes, math, strikethrough, task lists.
• Linting — lint(source) + a stateless LintRule protocol; a ruff-for-Markdown with three starter rules. See linting.
• Minimal dependencies — PyYAML for frontmatter; core parser is pure Python.

GFM-style features are available through plugins. Measured GFM 0.29 compliance is 654/672 (97.3%) with the GFM plugins enabled (Markdown(plugins=["table", "strikethrough", "task_lists", "autolinks"])); the remaining gap is the tagfilter extension, CommonMark 0.28-vs-0.31.2 emphasis drift, and a few autolink edge cases. See GFM compliance tracking.

Installation

pip install patitas

Requires Python 3.14+

Optional extras:

pip install patitas[syntax]      # Syntax highlighting via Rosettes
pip install patitas[all]         # All optional features

Quick Start

Parse and render

from patitas import parse, render

doc = parse("# Hello **World**")
html = render(doc)
# <h1 id="hello-world">Hello <strong>World</strong></h1>

Frontmatter

Parse YAML frontmatter from Markdown or other content, returning a (metadata, body) tuple:

from patitas import parse_frontmatter, extract_body

content = """---
title: Hello
weight: 10
---
# Body content
"""
metadata, body = parse_frontmatter(content)
# metadata: {"title": "Hello", "weight": 10.0}
# body: "# Body content"

# When YAML is broken, extract_body strips the --- block without parsing
body_only = extract_body(content)

Notebook support

Parse Jupyter notebooks (.ipynb) to Markdown content and metadata — stdlib JSON only:

from patitas import parse_notebook

with open("demo.ipynb") as f:
    content, metadata = parse_notebook(f.read(), "demo.ipynb")

# content: Markdown string (cells → fenced code, outputs → HTML)
# metadata: title, type, notebook{kernel_name, cell_count}, etc.

Security

Patitas is immune to ReDoS attacks.

Traditional Markdown parsers use regex patterns vulnerable to catastrophic backtracking:

# Malicious input that can freeze regex-based parsers
evil = "a](" + "\\)" * 10000

# Patitas: completes in milliseconds (no catastrophic backtracking)

Patitas uses a hand-written finite state machine lexer:

• Single character lookahead — No backtracking, ever
• Linear time for typical input — a few non-lexer paths remain super-linear on adversarial input; see Known limitations
• Safe for untrusted input — pair with input-size limits and timeouts; see Recommendations

⚠️ render() does not sanitize output. The default renderer is CommonMark-compliant and passes raw HTML and javascript:/data: URLs through verbatim. For untrusted content, sanitize the AST before rendering (or render to plain text with render_llm()):

from patitas import parse, render, sanitize
from patitas.sanitize import web_safe

doc = parse(untrusted_markdown)
# Strip HTML + disallowed URL schemes, then render HTML
html = render(sanitize(doc, policy=web_safe))

Learn more about Patitas security →

Performance

• 652 CommonMark examples — measure on your machine with benchmarks/benchmark_vs_mistune.py; recent Python 3.14.2 free-threaded local runs are in the low tens of milliseconds.

• Incremental parsing — For a 1-char edit in a ~100KB doc, parse_incremental is roughly 170x faster than full re-parse in the bundled benchmark (and up to ~430x for edits near the start of the document).

• Parallel scaling — Free-threaded speedups depend on Python build, hardware, corpus size, and optional comparator packages. Run python benchmarks/benchmark_parallel.py to see results on your machine. One recent local run on Python 3.14.2 with 1,000 CommonMark documents:

    Threads    Time      Speedup
    1          0.07s     1.00x
    2          0.05s     1.42x
    4          0.04s     1.64x
    8          0.04s     1.75x
  

# From repo (after uv sync --group dev):
python benchmarks/benchmark_vs_mistune.py
python benchmarks/benchmark_parallel.py   # Free-threading scaling
pytest benchmarks/benchmark_vs_mistune.py benchmarks/benchmark_incremental.py benchmarks/benchmark_directives.py benchmarks/benchmark_scaling.py benchmarks/benchmark_excerpt.py -v --benchmark-only --benchmark-group-by=group

See benchmarks/README.md for the full suite (pipelines, phase-breakdown, CI threshold checks).

Usage

from patitas import parse
from patitas.nodes import Heading, Paragraph, Strong

doc = parse("# Hello **World**")
heading = doc.children[0]

# Full type safety
assert isinstance(heading, Heading)
assert heading.level == 1

# IDE knows the types!
for child in heading.children:
    if isinstance(child, Strong):
        print(f"Bold text: {child.children}")

:::{note}
This is a note admonition.
:::

:::{warning}
This is a warning.
:::

:::{dropdown} Click to expand
Hidden content here.
:::

:::{tab-set}

:::{tab-item} Python
Python code here.
:::

:::{tab-item} JavaScript
JavaScript code here.
:::

:::

from patitas import Markdown, create_registry_with_defaults
from patitas.directives.decorator import directive

# Define a custom directive with the @directive decorator
@directive("alert")
def render_alert(node, children: str, sb) -> None:
    sb.append(f'<div class="alert">{children}</div>')

# Extend defaults with your directive
builder = create_registry_with_defaults()  # Has admonition, dropdown, tabs
builder.register(render_alert())

# Use it
md = Markdown(directive_registry=builder.build())
html = md(":::{alert} This is important!\n:::")

from patitas import Markdown

md = Markdown(highlight=True)

html = md("""
```python
def hello():
    print("Highlighted!")

Uses [Rosettes](https://github.com/lbliii/rosettes) for O(n) highlighting.

</details>

<details>
<summary><strong>Free-Threading</strong> — Python 3.14t</summary>

```python
from concurrent.futures import ThreadPoolExecutor
from patitas import parse

documents = ["# Doc " + str(i) for i in range(1000)]

with ThreadPoolExecutor() as executor:
    # Safe to parse in parallel — no shared mutable state
    results = list(executor.map(parse, documents))

from patitas import parse, sanitize, render_llm
from patitas.sanitize import llm_safe

doc = parse(user_content)
clean = sanitize(doc, policy=llm_safe)  # Strip HTML, dangerous URLs, zero-width chars
safe_text = render_llm(clean, source=user_content)

Migrate from mistune

Same API — swap the import:

from patitas import Markdown
md = Markdown()
html = md(source)

Full migration guide →

The Bengal Ecosystem

A structured reactive stack — every layer written in pure Python for 3.14t free-threading.

Python-native. Free-threading ready. No npm required.

Development

git clone https://github.com/lbliii/patitas.git
cd patitas
uv sync --group dev
pytest

Run benchmarks (after uv sync --group dev):

python benchmarks/benchmark_vs_mistune.py
python benchmarks/benchmark_parallel.py   # Free-threading scaling demo
pytest benchmarks/benchmark_*.py -v --benchmark-only --benchmark-group-by=group   # Full suite

License

MIT License — see LICENSE for details.