permitd

Governed tool execution for agent loops.

Your agent loop wants to send the email, write the file, hit the API. You want a human decision in between — one that the model cannot skip, replay, or bend to different arguments — and a line in an audit log either way. (THREAT_MODEL.md says exactly when that is a boundary and when it is a guardrail.)

propose(tool, args) ──> permit (signed, TTL, single-use)
                   ──> approve   (a human, out-of-band: CLI, or any callable)
                   ──> execute   (verify + burn, atomically)
                   ──> one audit line lands (append-only JSONL)

permitd is that flow as a small, stdlib-only Python library. It is also loop state: the permit lives in SQLite, so a call proposed in turn N of your agent loop is approved from another terminal and executed in turn N+K — across restarts, across processes.

Every non-execute outcome is fail-closed. A missing, expired, denied, tampered, argument-mismatched, or already-used permit is refused, and the refusal is audited too.

Install

pip install permitd

Python ≥ 3.10, zero dependencies.

Related MCP server: AgentGate

Sixty seconds, two terminals

Terminal 1 — the agent side (agent.py):

import time
from permitd import Gate, RED

gate = Gate(db="permitd.db")

@gate.tool(tier=RED, description="send a message to someone")
def send_message(to, body):
    return f"delivered to {to}: {body!r}"

args = {"to": "alice", "body": "hello from the loop"}
r = gate.call("send_message", args)
print(r.error)                       # "... permit PRM-xxxx is proposed ..."

pid = r.permit["id"]
while gate.get(pid).status == "proposed":   # this state survives restarts
    time.sleep(1)

r = gate.call("send_message", args, permit_id=pid)
print(r.result if r.ok else r.error)

python agent.py

Terminal 2 — the human side:

$ permitd pending
1 pending permit(s):
  PRM-3f9c21ab44de  [proposed]  send_message
      args: {"to": "alice", "body": "hello from the loop"}
      proposed: 2026-07-29T18:12:03+00:00  ttl: 300s

$ permitd approve PRM-3f9c21ab44de
approved — PRM-3f9c21ab44de is executable for 300s, single use, bound to exactly these arguments

Terminal 1 wakes up and prints delivered to alice: 'hello from the loop'. The trail:

$ permitd audit
{"ts": "...", "event": "proposed", "permit_id": "PRM-3f9c21ab44de", "tool": "send_message", ...}
{"ts": "...", "event": "approved", "permit_id": "PRM-3f9c21ab44de", ...}
{"ts": "...", "event": "executed", "permit_id": "PRM-3f9c21ab44de", "ok": true}

That is the whole product: propose, approve, execute, audit line.

What the permit actually guarantees

• Bound to exact arguments. A permit is scoped to sha256(tool + canonical_json(args)). Approval for "send X to Alice" cannot be replayed as "send Y to Eve" — key order and whitespace don't change the binding; any value change does (args_mismatch).

• Single-use, atomically. The burn is one SQLite compare-and-swap (UPDATE ... WHERE status='approved'), so two processes racing the same permit cannot both pass (already_used).

• Time-boxed twice. A proposal is approvable for ttl_seconds (default 300); a minted approval is executable for another ttl_seconds. Unparseable timestamps count as expired.

• HMAC-signed. Approval mints HMAC-SHA256(secret, id.binding_hash.approved_at), re-verified at execute time — a store row edited behind the kernel's back fails (bad_signature).

• Hash-chained audit. Every audit line carries the SHA-256 of the line before it. Edit, reorder, or delete any line but the newest and permitd audit --verify names the line where the chain breaks. Anchor permitd audit --tip off-host and truncation of the newest lines is caught too. Tamper-evident, not tamper-proof (see THREAT_MODEL.md).

• Fail-closed everywhere. Anything the kernel cannot positively verify — including "the arguments could not even be inspected" — is a refusal, not a pass. Refusals are audited with their reason.

Tiers

Gate is a small registry with three tiers over the kernel:

If you don't want the registry, use the kernel directly:

from permitd import PermitKernel, SqliteStore, AuditLog

kernel = PermitKernel(SqliteStore("permitd.db"),
                      secret_path="permitd.db.secret",
                      audit=AuditLog("permitd_audit.jsonl"))
p = kernel.propose("deploy", {"target": "prod"})
kernel.approve(p.id)                      # or from the CLI / your own UI
kernel.execute("deploy", {"target": "prod"}, p.id, runner=do_deploy)

approve is just a method on a store-backed kernel — call it from a CLI, a Slack handler, an HTTP endpoint, wherever your human is.

The egress guard

Before any non-GREEN call runs — including at propose time — its arguments are scanned for credential-shaped content: private-key blocks, Bearer/Basic headers, AWS/GitHub/Slack/Stripe/OpenAI/Anthropic/Google key shapes, inline api_key=... assignments, the values of this process's own sensitive environment variables, and a conservative high-entropy backstop. A poisoned context that steers a secret into a tool argument is refused before anything leaves, before any approval card is shown, and the refusal reason names the matched shape, never the value.

MCP: gate any agent's tools, including Claude Code's

Five-minute walkthrough: docs/quickstart-claude-code.md.

examples/mcp_server/ is an MCP server whose tools go through the gate. Point any MCP-speaking agent at it and that agent gets propose → approve → execute + audit with zero agent-side changes: the agent calls a RED tool, is told "permit PRM-… proposed, waiting for approval", you run permitd approve PRM-… in another terminal, the agent retries and the call executes. The audit line lands either way.

Storage

SqliteStore (default, durable, atomic burn) and MemoryStore (tests, ephemeral) ship in the box. Anything else needs five methods — see the PermitStore protocol in store.py; keep burn compare-and-swap or you lose the one-shot guarantee.

The audit trail is a separate append-only JSONL file so it stays tail -f-able. Each line's prev field is the hash of the previous line:

$ permitd audit --verify
ok — 4 line(s), chain intact, tip 9b1c…e4
$ permitd audit --tip        # store this somewhere the writer can't reach
9b1c…e4

Writes are best-effort by contract (an audit failure never blocks a call); AuditLog.dropped counts any lines lost that way.

What permitd is not

Not an agent, not a framework, not memory, not RAG. It has no opinion about your loop, your model, or your prompts. It is the layer that holds the state of "may this run?" across turns — and the receipt after it did. What it does and does not defend against: THREAT_MODEL.md.

Ancestry

Extracted from the tool-governance kernel of brainfoundry-nous, where it runs in production gating a personal AI node's tools. The propose/confirm/execute + audit grammar goes back to hbar.brain.console (2026-03). Design notes: DESIGN.md.

License

MIT.