ABNF

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ABNF generates parsers from ABNF grammars as described in RFC 5234 and RFC 7405. Its main purpose is parsing data specified in RFCs — HTTP headers, email addresses, URIs, and the like — but it handles any ABNF grammar. It ships with 30+ ready-to-use grammar modules for common RFCs and has been in production use since it was first written for parsing HTTP headers in a web framework.

Installation

pip install abnf
pip install 'abnf[rust]'   # optional Rust backend, for substantially faster parsing

ABNF is tested with Python 3.10–3.14.

Quick start

from abnf.grammars import rfc7232

# parse an ETag header value
node, offset = rfc7232.Rule("ETag").parse('W/"moof"', 0)
print(node.value)          # 'W/"moof"'

# validate a whole string against a rule (raises ParseError otherwise)
from abnf.grammars import rfc5322
rfc5322.Rule("address").parse_all("test@example.com")

# compile your own rule; the RFC 5234 core rules are always available
from abnf import Rule
greeting = Rule.create('greeting = "hello" SP 1*ALPHA')
greeting.parse_all("hello world")

Parsing bytes

abnf parses code points, so parse and parse_all take a str. To parse wire data, decode it with latin-1 — that maps the 256 byte values onto U+0000–U+00FF one to one, so a code point is exactly an octet and octet-oriented grammars behave as their RFCs describe:

rfc7230.Rule("request-line").parse_all(raw.decode("latin-1"))

See What abnf parses for why the encoding is the caller's choice.

Documentation

Full documentation is hosted at abnf.readthedocs.io and follows the Diátaxis framework:

  • Tutorial — Parse your first header, a ten-minute end-to-end walkthrough.
  • How-to guides — validate input, extract values with visitors, load a grammar from a file, write your own grammar module, exclude matches from a rule, use the Rust backend.
  • Reference — the public API, the built-in core rules, the bundled grammars, and configuration knobs.
  • Explanation — what abnf parses (code points, not bytes), the combinator architecture, the two backends, alternation semantics, and how backtracking is kept in check.

To build the docs locally:

pip install -e '.[docs]'
sphinx-build -W docs docs/_build/html

Contributing

Set up a development environment with the dev extra:

pip install -e '.[dev]'          # or: uv sync --extra dev

Run the test suite (skip the slower fuzz tests with --ignore=tests/fuzz):

pytest --cov-report term-missing --cov=abnf

Pre-commit hooks run ruff, pyright, check-manifest, and tox. Install them once with pre-commit install. See the Explanation and How-to docs for working with the Rust backend.

Third-party packages

Project links

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  • Released:
Newer release available (2.8.2)

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Credits

Author: Charles Yeomans

GitHub Statistics

Data verified by PyPI on Aug 14, 2026
The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License

MIT License

Requires

Python >=3.10

Provides Extra

dev rust docs

Tags

abnf generator parser

Classifiers

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