A pure Python HTML5 parser that just works.
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JustHTML
JustHTML is a pure Python HTML5 parser that just works. It parses HTML and returns a DOM tree that you can traverse and manipulate.
Why JustHTML?
1. ✅ Correctness: 100% Spec Compliant
JustHTML is built to be correct. It implements the official WHATWG HTML5 specification exactly (tree builder and tokenizer), including all the complex error-handling rules that browsers use.
- Verified Compliance: Passes all 8,500+ tests in the official
html5lib-testssuite (used by browser vendors) (see /tests/). - 100% Coverage: Every single line and branch of code is covered by integration tests.
- Fuzz Tested: Has parsed 3 million randomized broken HTML documents to ensure it never crashes or hangs (see fuzz.py).
- Living Standard: It tracks the living standard, not a snapshot from 2012.
2. 🐍 Pure Python with zero dependencies
JustHTML has zero dependencies. It's pure Python.
- Easy Installation: No C extensions to compile, no system libraries (like libxml2) required. Works on PyPy, WASM (Pyodide), and anywhere Python runs.
- No dependency upgrade hassle: Some libraries depend on a large set of libraries, all which require upgrades to avoid security issues.
- Debuggable: It's just Python code. You can step through it with a debugger to understand exactly how your HTML is being parsed.
- Returns plain python objects: Other parsers return lxml or etree trees which means you have another API to learn. JustHTML returns a set of nested objects you can iterate over. Simple.
3. ⚡ Fast enough™ Performance
If you need to parse terabytes of data, use a C or Rust parser (like html5ever). They are 10x-20x faster (see benchmarks.py).
But for most use cases, JustHTML is fast enough. It parses the Wikipedia homepage in ~0.1s. It is the fastest pure-Python HTML5 parser available, outperforming html5lib and BeautifulSoup.
Comparison to other parsers
| Parser | Spec Compliant? | Pure Python? | Speed | Notes |
|---|---|---|---|---|
| JustHTML | ✅ Yes | ✅ Yes | ⚡ Fast | The sweet spot. Correct, easy to install, and fast enough. |
html.parser |
❌ No | ✅ Yes | ⚡ Fast | Standard library. Chokes on malformed HTML. |
lxml |
❌ No | ❌ No | 🚀 Very Fast | C-based. Fast but not spec-compliant (different output than browsers). |
html5lib |
✅ Yes | ✅ Yes | 🐢 Slow | The reference implementation. Very correct but very slow. |
BeautifulSoup |
N/A | N/A | 🐢 Slow | Wrapper around other parsers. Slower and more memory hungry than the underlying parser. |
gumbo / html5ever |
✅ Yes | ❌ No | 🚀 Very Fast | C/Rust based. Fast and correct, but requires compiling extensions. |
Installation
pip install justhtml
Example usage
Python API
from justhtml import JustHTML
html = "<html><body><div id='main'><p>Hello, <b>world</b>!</p></div></body></html>"
doc = JustHTML(html)
# 1. Traverse the tree
# The tree is made of SimpleDomNode objects.
# Each node has .name, .attrs, .children, and .parent
root = doc.root # #document
html_node = root.children[0] # html
body = html_node.children[1] # body (children[0] is head)
div = body.children[0] # div
print(f"Tag: {div.name}")
print(f"Attributes: {div.attrs}")
# 2. Pretty-print HTML
# You can serialize any node back to HTML
print(div.to_html())
# Output:
# <div id="main">
# <p>
# Hello,
# <b>world</b>
# !
# </p>
# </div>
Command Line Interface
You can also use JustHTML from the command line to pretty-print HTML files:
# Parse a file
python -m justhtml index.html
# Parse from stdin (great for piping)
curl -s https://example.com | python -m justhtml -
Develop locally and run the tests
-
Clone the repository:
git clone git@github.com:EmilStenstrom/justhtml.git cd justhtml
-
Install the library locally (there's no dependencies!):
pip install -e .
-
Run the tests:
python run_tests.pyFor verbose output showing diffs on failures:
python run_tests.py -v
-
Run the benchmarks:
python benchmark.py
License
MIT. Free to use for commercial and non-commercial use.
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