vda-witness 0.1.0

VDA Witness SDK — seal your AI agent's decisions into tamper-evident, Ed25519-signed, independently-verifiable evidence (EU AI Act Art. 12). Fail-open, zero-config. Part of the Verified Digital Agents (VDA) platform.

vda-witness (Python SDK)

Seal your AI agent's decisions into tamper-evident, Ed25519-signed, independently-verifiable evidence — the records EU AI Act Article 12 requires. Part of the Verified Digital Agents (VDA) platform; VDA Witness is its evidence layer.

• Fail-open: sealing never raises and never blocks your agent.
• Zero-config, zero-dependency: one import, set WITNESS_API_KEY, standard library only.
• Independently verifiable: anyone can verify a record offline, without trusting VDA.

⚠️ Read this first — what you get out of the box (custody)

Out of the box, sealing goes to the hosted Witness service on the custodial / ephemeral (test) tier: records are signed by the Witness service, not by a key you control. Every such record honestly carries custody: "custodial" and says so in plain text.

This is for building and testing. It is NOT customer-controlled signing and is NOT compliance-grade EU AI Act Article-12 evidence — do not present ephemeral custodial records to an auditor as your own controlled evidence.

For compliance-grade evidence, use customer-managed signing — you control the private key, records carry custody: "customer-managed" ("customer-controlled signing"), and Witness never sees your key. That is the tier you put in front of an auditor.

Tier	Who holds the key	Record label	Use for
Custodial (default/ephemeral)	Witness service	custodial	build & test
Customer-managed	You	customer-managed	compliance-grade evidence

Install

pip install vda-witness

First seal (copy-paste — works as-is)

from vda_witness import Witness

witness = Witness()  # reads WITNESS_API_KEY

witness.seal(
    decision={"agent": "Refund Agent", "inputs": {"amount_eur": 150},
              "verdict": "PASS", "reasoning": "<= 200 and account in good standing"},
    governing_rule={"ruleId": "refund.auto",
                    "ruleText": "Agents MAY auto-approve refunds up to EUR200 where the account is in good standing."},
)

Decorate an existing agent (code unchanged beyond the decorator)

@witness.witnessed(
    to_decision=lambda args, kwargs, result: {
        "agent": "Refund Agent", "inputs": kwargs,
        "verdict": result["verdict"], "reasoning": result["why"],
    },
    rule={"ruleId": "refund.auto", "ruleText": "Agents MAY auto-approve refunds up to EUR200 ..."},
)
def decide(**request):
    ...  # your agent, untouched — sealed automatically after it returns (fail-open, bounded)

Framework adapters

from vda_witness import witness_openai
witness_openai(client, witness, {"ruleId": "assistant.sop", "ruleText": "..."})  # seals each chat.completions.create

Anthropic, LangChain, CrewAI, and the Vercel AI SDK use the same wrap-and-seal pattern (witness.witnessed(...)); typed adapters ship per release.

Verify (no auth — the trust proposition)

witness.verify(record=my_record)   # {"ok": True} — and False if anything changed

Options

Witness(api_key=None, base_url="https://witness.getvda.ai", timeout=3.0, fire_and_forget=False, on_error=None). Set fire_and_forget=True for zero added latency (seal on a background thread).

Honest scope: Witness produces the evidence (Art. 12 record-keeping), not a compliance certificate. The Article 12 Evidence Report is generated from your sealed trail; Compliance Officer attestation makes it a regulatory artefact.