jacs 0.11.2

JACS - JSON AI Communication Standard: Cryptographic signing and verification for AI agents.

JACS Python Library

Cryptographic identity, signing, and verification for AI agents from Python.

pip install jacs

Prebuilt native bindings are distributed via maturin. A normal install does not require compiling Rust.

Full documentation | Quick Start

Quick start

import jacs.simple as jacs

info = jacs.quickstart(name="my-agent", domain="my-agent.example.com")
signed = jacs.sign_message({"action": "approve", "amount": 100})
result = jacs.verify(signed.raw)
print(f"Valid: {result.valid}, Signer: {result.signer_id}")

quickstart() creates a persistent agent with keys on disk. If jacs.config.json exists, it loads it; otherwise it creates a new agent.

Core operations

Operation	Description
quickstart(name, domain)	Create or load a persistent agent
load()	Load an existing agent from config
sign_message()	Sign JSON-serializable data
sign_file()	Sign a file with optional embedding
verify()	Verify a signed document
verify_standalone()	Verify without loading an agent
create_agreement_v2()	Create a standalone Agreement v2 document
sign_agreement_v2()	Sign as signer, witness, or notary
verify_agreement_v2()	Verify Agreement v2 hash, policy, transcript, and status
export_agent()	Export agent JSON for sharing
audit()	Run a security audit

Text and image provenance

Python exposes the same inline text and image signing surface as the CLI:

import jacs.simple as jacs
from jacs import MissingSignatureError

jacs.load("./jacs.config.json")

# Markdown/text: append and verify an inline signature block.
jacs.sign_text("README.md")
text = jacs.verify_text("README.md")
print(text.status)  # 'signed' | 'missing_signature' | 'malformed'

try:
    jacs.verify_text("README.md", strict=True)
except MissingSignatureError:
    print("not signed")

jacs.verify_text("README.md", key_dir="./trusted-keys/")

# Images: embed and verify a signature in PNG, JPEG, or WebP metadata.
jacs.sign_image("photo.png", out="signed.png")
image = jacs.verify_image("signed.png")
print(image.status)  # 'valid'

payload = jacs.extract_media_signature("signed.png")

The same methods are available on the instance-based JacsClient for multi-agent processes. These signatures prove that an agent signed specific canonical bytes at its claimed time; they do not prove first creation or legal ownership.

Verify without an agent

result = jacs.verify_standalone(signed_json, key_directory="./keys")

Cross-language interop is tested on every commit. Documents signed in Rust or Node.js verify in Python, and Python-signed documents verify in the other bindings.

Agreement v2

Use Agreement v2 for new multi-agent consent workflows:

from jacs import SimpleAgent

agent, info = SimpleAgent.ephemeral(algorithm="ed25519")
agent_id = info["agent_id"]

agreement = agent.create_agreement_v2({
    "title": "Refund approval",
    "description": "Approval for a bounded refund.",
    "terms": "Refund up to $25 for order 123.",
    "status": "proposed",
    "parties": [{"agentId": agent_id, "agentType": "ai", "role": "signer"}],
    "signaturePolicy": {"partyQuorum": "all", "witnessRequired": 0, "notaryRequired": 0},
    "controllers": [agent_id],
})

signed = agent.sign_agreement_v2(agreement, "signer")
assert agent.verify_agreement_v2(signed)["valid"]

The same operations are available as module-level functions once an agent is loaded (quickstart() / create() / load()), matching Node's @hai.ai/jacs/simple surface:

import jacs.simple as jacs

jacs.quickstart(name="my-agent", domain="agent.example.com")
agent_id = jacs.get_agent_info().agent_id

agreement = jacs.create_agreement_v2({
    "title": "Refund approval",
    "description": "Approval for a bounded refund.",
    "terms": "Refund up to $25 for order 123.",
    "status": "proposed",
    "parties": [{"agentId": agent_id, "agentType": "ai", "role": "signer"}],
    "signaturePolicy": {"partyQuorum": "all", "witnessRequired": 0, "notaryRequired": 0},
    "controllers": [agent_id],
})

signed = jacs.sign_agreement_v2(agreement, "signer")
assert jacs.verify_agreement_v2(signed)["valid"]

Verifying another agent's agreement signature requires that agent's public key, so distinct agents must share a data_directory or exchange public keys; ephemeral agents verify only their own signatures.

The older create_agreement() / sign_agreement() / check_agreement() methods remain for simple jacsAgreement sidecars on existing documents.

Framework adapters

pip install jacs[langchain]    # LangChain / LangGraph
pip install jacs[fastapi]      # FastAPI / Starlette
pip install jacs[crewai]       # CrewAI
pip install jacs[anthropic]    # Anthropic / Claude SDK
pip install jacs[a2a]          # A2A protocol
pip install jacs[all]          # Everything

Instance-based API

For multiple agents in one process:

from jacs.client import JacsClient

client = JacsClient.quickstart(name="my-agent", domain="example.com")
signed = client.sign_message({"action": "approve"})

See DEVELOPMENT.md for the full API reference, advanced usage, framework adapter examples, and testing utilities.

Links

• JACS Documentation
• Verification Guide
• Framework Adapters
• Source
• Examples