atheris

library3.1.0pypypi✓ verified 84d ago

A coverage-guided fuzzer for Python and Python extensions, developed by Google. It integrates with libFuzzer and supports fuzzing Python code and native extensions. Version 3.0.0; released active, follow-on of stable API.

testing

pip install atheris

github ↗package ↗

INSTALL

IMPORT

SIG · ATHERIS

atheris

testingpythonv3.1.0

Install

2.5s avg

Import

107ms

Disk

148MB

Pass rate

3/ 10

Env Coverage3 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v3.0.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

glibc

py 3.10

✕ build_error

py 3.11

✕ build_error

✓ 2.4s

py 3.12

✕ build_error

✓ 2.4s

py 3.13

✕ build_error

✓ 2.6s

py 3.9

✕ build_error

148MB installed

● package 148MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

atheris

✓ import atheris

Setup

✓ from atheris import Setup

FuzzedDataProvider

✓ from atheris import FuzzedDataProvider

Mutate

✓ from atheris import Mutate

Deprecated in v3; use FuzzedDataProvider instead

Basic fuzzer with FuzzedDataProvider.

import atheris import sys def TestOneInput(data): fdp = atheris.FuzzedDataProvider(data) if len(data) >= 2 and data[0] == ord('b') and data[1] == ord('u'): raise RuntimeError('Bug!') atheris.Setup(sys.argv, TestOneInput) atheris.Fuzz()

Debug

Known issues

deprecatedatheris.Mutate is deprecated in v3. Use FuzzedDataProvider for structured mutation.

fix

Replace any usage of atheris.Mutate with FuzzedDataProvider methods (e.g., ConsumeInt, ConsumeString, etc.).

affects: >=3.0.0

breakingIn v3, the way FuzzedDataProvider is initialized changed. old: atheris.FuzzedDataProvider(data, to_use_bytes) no longer valid.

fix

Instantiate as FuzzedDataProvider(data) and use its methods.

affects: >=3.0.0

gotchaatheris requires a recent C++ compiler and libFuzzer support. It may not install on Windows or older Linux. Use manylinux wheels or compile from source.

fix

On Linux, ensure clang and libfuzzer-dev are installed. For Windows, use WSL.

affects: all

gotchaCorpus directory: if not specified, atheris uses default; but crashes saved to current directory. Ensure write permissions.

fix

Pass a corpus directory to Setup: atheris.Setup(sys.argv, TestOneInput, corpus_prefix='corpus/')

affects: all

breakingIn v2, the TestOneInput function signature was different: it took two arguments (data and size). v3 expects one argument (bytes).

fix

Define TestOneInput(data) with a single parameter.

affects: >=3.0.0

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'atheris'

atheris is not installed or not available for the current platform.

fix

Install with pip install atheris. On Linux, install clang and libfuzzer-dev. On macOS, it works. On Windows, use WSL.

ImportError: cannot import name 'FuzzedDataProvider' from 'atheris'

Version <3.0.0: FuzzedDataProvider was not available. Or using wrong import path.

fix

Upgrade atheris: pip install --upgrade atheris, and use from atheris import FuzzedDataProvider.

TypeError: TestOneInput() takes 2 positional arguments but 3 were given

User defined TestOneInput with two parameters (data, size) but atheris v3 expects one parameter.

fix

Change function signature to TestOneInput(data). Use FuzzedDataProvider to extract size if needed.

RuntimeError: Atheris requires libFuzzer, but it is not available

libFuzzer not found at runtime, typically because compiler not configured with -fsanitize=fuzzer.

fix

Build/install atheris with the correct sanitizer flags. For pip, ensure clang is installed and libfuzzer-dev is present.

Upgrade

Version history

3.1.0latest on PyPI · released Jun 17, 2026

Audit

Dependencies

No dependency data recorded yet.

Agent activity

18 hits · last 30 days

node

OpenAI (training)

Resources

githubhttps://github.com/google/atheris ↗

packagehttps://pypi.org/project/atheris/ ↗