Pigeon, a signed Pass for what a sub-agent may do

Pigeon Your agent spawned a sub-agent and handed it the same API key. That sub-agent can now deploy to production, read the payments database, and merge to main. Pigeon stops that. You hand the child a Pigeon Pass: a narrowed, signed credential for what it may do, not a copy of everything you can do. Install Python 3.12 or newer. git clone https://github.com/pigeonlabsHQ/pigeon.git cd pigeon pip install . The whole idea, in 20 lines from pigeon import grant, verify authority = grant( subject="agent:deployer", capabilities=["deploy"], resources=["environment:staging"], ) allowed = verify(authority, action="deploy", resource="environment:staging") assert allowed.allowed denied = verify(authority, action="deploy", resource="environment:production") assert not denied.allowed assert denied.reason_code == "RESOURCE_NOT_ALLOWED" print(denied.reason_code, denied.message, denied.details) verify never returns a bare boolean. A denial includes a reason code, a message, and the comparison that failed (requested vs allowed). Try it without writing that yourself: python examples/01_infrastructure.py python demo/agent.py Where it goes in an agent There is no Pigeon server to connect to. You change two places you already have: Spawn. Where you would have copied an API key into a sub-agent, call delegate(...) and give the child a Pass. Tool. Where the side effect happens (deploy, query, MCP tool), call verify(...) and do not run the tool if it is denied. Keep the real secret on the runner. The child carries the Pass. from pigeon import delegate, grant, verify, DelegationError parent = grant( subject="agent:orchestrator", capabilities=["deploy", "open_pr"], resources=["environment:staging", "repo:acme/api"], constraints={"max_deploys_per_hour": 3}, ) worker = delegate( parent, subject="agent:pr-bot", capabilities=["open_pr"], resources=["repo:acme/api"], constraints={"max_deploys_per_hour": 3}, # cannot drop a parent constraint ) result = verify(worker, action="open_pr", resource="repo:acme/api") assert result.allowed denied = verify(worker, action="deploy", resource="environment:staging") assert denied.reason_code == "CAPABILITY_NOT_GRANTED" try: delegate(worker, "agent:rogue", ["open_pr", "deploy"], ["repo:acme/api"]) except DelegationError as exc: assert exc.reason_code == "PRIVILEGE_ESCALATION" A child cannot add capabilities, widen resources, raise a bound, or drop a parent constraint. If Pigeon cannot prove the child is narrower, it rejects. If the runner never calls verify, the Pass is decoration. MCP middleware This is an enforcement point, not part of the protocol. The client mints a narrower Pass per tool call. The server verifies it before the tool runs. from pigeon import grant from pigeon.integrations.mcp import execute_tool, pass_for_tool parent = grant( subject="agent:github", capabilities=["create_issue", "merge_pr"], resources=["mcp:github"], ) tool_pass = pass_for_tool(parent, "create_issue", "mcp:github") def create_issue(*, title, body): return {"created": True, "title": title} ok = execute_tool(tool_pass, "create_issue", "mcp:github", {"title": "bump deps", "body": "automated"}, create_issue) assert ok["allowed"] no = execute_tool(tool_pass, "merge_pr", "mcp:github", {"title": "nope", "body": "nope"}, create_issue) assert no["reason_code"] == "CAPABILITY_NOT_GRANTED" Identity tells you who the agent is. Authority tells you what it may do. CLI pigeon keygen pigeon inspect pass.json What this is not Pigeon is a small primitive. It is not a platform, a policy engine, an identity provider, or a key custodian. It does not stop prompt injection. It bounds blast radius along the dimensions you put on the Pass, and only those. Protocol: SPEC.md Limits: SECURITY.md More scripts: examples/ (infrastructure, data, code, then payments)