drift — mandate gate for AI agents

npx add-mcp 'https://drift.rta.lat/mcp'

drift

Continuous mandate enforcement for AI agents. Every action is checked against the signed mandate before it happens, not once at signing.

pip install drift          # or: pip install -e .
python3 -m drift.http_server --http 8080

The gap

An agent is granted a mandate: who to pay, how much, in which currency, until when. AP2 verifies that mandate once, at signature time. After that the agent acts alone, and nothing holds it inside its authority.

Measured proof that this matters, from the AP2 Python SDK itself:

verify_chain documents:
  "enforcing expected_aud / expected_nonce on the terminal hop when provided"

but kb_sd_jwt.verify calls verify_expected_claims only when typ in TYP_TERMINAL,
and a kb+sd-jwt+kb token — which the SDK itself produces whenever the payload
carries a cnf — falls into TYP_INTERMEDIATE:

  hop type      : kb+sd-jwt+kb
  aud in token  : https://attacker.example/ap2
  expected_aud  : https://honest-merchant.example/ap2
  ACCEPTED a token with the wrong audience.

The protocol an agent trusts with its spending authority does not check that the authority was not substituted. drift checks it.

What it checks

#	rule	catches
1	amount	over the limit — the most common form of drift
2	payee	wrong recipient
3	audience	payment redirected to someone else
4	currency	currency substituted
5	window	outside the validity period
6	intent	intent outside the allowlist

Default is DENY. Rules run in fixed order, so a refusal names the most important reason rather than an incidental one.

MCP tools

tool	purpose
drift_check	check one action against a mandate
drift_session	check a sequence, get a report with a chain fingerprint
drift_explain	show the rules in the order they apply

No SSE, no stateful sessions, no HTTP framework. Standard library only.

Example

from drift import Mandate, Drift, Action

m = Mandate(
    payee_id="shop", audience="https://merchant.example/ap2",
    max_amount_minor=10_000, currency="USD",
    valid_from=1_700_000_000, valid_until=1_700_086_400,
    allowed_intents=("buy",),
)
d = Drift(m)
verdict, rule = d.submit(Action(
    intent="buy", payee_id="shop", audience="https://merchant.example/ap2",
    amount_minor=99_999, currency="USD", at=1_700_000_060,
))
print(verdict, rule)   # DENY amount

Limits, stated plainly

• Does not verify mandate signatures. That is AP2's job. drift runs after signature verification, at the level of decisions.
• Does not execute. It decides; the caller acts.
• Does not keep state. A session is an argument. No state means no attack surface and no divergence under replication.
• Does not tell truth from intent. intent arrives from the agent and is untrusted input. drift bounds the damage; it does not certify the intent.

If an agent controls both intent and amount, it can lie in both. Closing that gap is attest's job: attest proves afterwards, drift bounds beforehand. They are complements.

Use it from your agent

{
  "mcpServers": {
    "drift": { "url": "https://drift.rta.lat/mcp" }
  }
}

That block is how our own agents call this server. Tools: drift_check (one action), drift_session (a sequence), drift_explain (the six rules and why each exists). 100 free checks per day, then $0.005 per call over x402.

Licence

Apache-2.0.