ja3-client (Python)

Browser TLS/H2/H3 fingerprint impersonation from Python, through a ctypes binding to the Go shared library. Pure standard library - no build step, no dependencies. The ABI contract (payload keys, response envelope, error codes) is in cffi/README.md; this file covers installing the binary the binding needs.

from ja3_client import Ja3

ja3 = Ja3()
resp = ja3.request("https://tls.browserleaks.com/json", impersonate="chrome_153")
print(resp.json()["ja3n_hash"])

with ja3.session(impersonate="chrome_133") as session:
    session.get("https://example.com/")            # same pool + cookie jar

Where the library comes from

pip install ja3-client installs binding code only. A wheel cannot run code at install time, so the native library is fetched the first time Ja3() is constructed: the resolver downloads ja3-client-<version>-<os>-<arch>.zip from this repository's GitHub Release for the installed version, checks it against the release's SHA256SUMS.txt, and unpacks the library into a cache shared with the Node and C# bindings:

~/.cache/ja3-client/<version>/<os>-<arch>/    (macOS: ~/Library/Caches, Windows: %LOCALAPPDATA%)

To fetch it explicitly - before a container build, or on a machine that will later be offline:

ja3-client ensure          # or: python -m ja3_client_binaries ensure
ja3-client print-url       # the archive this machine wants
ja3-client status          # version, slug, cache dir, what is present

At runtime the binding looks for, in order: the library_path you pass to Ja3(), JA3_CLIENT_LIB, a library beside it or under cffi/build, any version in the shared cache, and only then a download.

Knobs

No network, no GitHub

Build it and pin it, or unzip a release archive and point JA3_CLIENT_LIB at the file inside - every archive carries smoke.py, which proves the download offline:

git clone https://github.com/smallerqiu/ja3-client && cd ja3-client/cffi && make host
export JA3_CLIENT_LIB="$PWD/build/darwin/ja3_client_arm64.dylib"   # linux: libja3_client_amd64.so

Linux archives are built against glibc (Debian bookworm); on musl (Alpine) build the library yourself.