Native library reference. Extended CLI examples use jacs-compat. This source reference can include unreleased changes; see the package guide for installation and MCP profiles for available tools.

Python Installation

Install the published native package:

python -m pip install jacs==0.16.1

Published 0.16.1 wheels support Python 3.11–3.14 on macOS arm64/x86_64, Linux arm64/x86_64 glibc, and Linux x86_64 musl; this checkout has the same Python requirement. A compatible wheel needs no Rust compiler. See the release inventory for platform evidence; later source changes are not automatically in the wheel.

Try signing

from jacs.client import JacsClient

client = JacsClient.ephemeral()
signed = client.sign_message({"message": "Hello from Python"})
assert client.verify(signed.raw).valid

For an identity that survives process restarts:

client = JacsClient.quickstart(name="my-agent", domain="my-agent.example.com")
signed = client.sign_message({"message": "Persistent identity"})
assert client.verify(signed.raw).valid

New agents default to pq2025 (ML-DSA-87). Quickstart loads an existing configuration or creates encrypted keys. Preserve the password through a host secret source or keychain; an automatically generated password may otherwise survive only in-process. See native password bootstrap.

Optional integrations

python -m pip install "jacs[mcp]"
python -m pip install "jacs[fastapi]"
python -m pip install "jacs[langchain,langgraph]"
python -m pip install "jacs[anthropic]"
python -m pip install "jacs[a2a-server]"

Install only the extras you need. The a2a extra adds no dependencies; a2a-server supplies FastAPI and Uvicorn.

CLI and source builds

The Python jacs command downloads and caches the matching CLI release on first use and verifies its SHA-256. Importing the library downloads nothing. Unsupported platforms fail; no musl CLI archive is published. Alternatively install the portable CLI with cargo install jacs-cli and start its verify-only MCP server with jacs mcp. If the Python shim shadows Cargo's binary, invoke the binary in Cargo's bin directory explicitly.

Native configuration commands belong to the separate compatibility CLI: cargo install jacs-cli-compat installs jacs-compat. Prefer the Python quickstart above to create a Python agent.

For source builds, follow the native development guide from the complete repository. Native bindings use a separate Cargo workspace.

Continue with Basic Usage, MCP, or Framework Adapters.