Verifiable handoffs between agents.

What Padlock does

Padlock gives two agents a shared, ordered record of a handoff — and a way for the receiver to check that nothing in that record was altered after it was written.

1. 01 · WRITE

   Write the handoff

   The sending agent appends blocks to a pad. Block 0 is a strict locker.handoff.v1 envelope: task id, from/to agents, constraints, artifacts, budget.

2. 02 · SEAL

   Seal the pad

   Sealing freezes the pad and revokes further writes. The pad's head_hash — the hash of its latest block — becomes fixed.

3. 03 · HANDOFF

   Pass a read ticket

   The receiver gets a scoped read ticket, not the write key. A read_once ticket opens a short read lease; a read_unlimited ticket can be minted for a durable audit.

4. 04 · VERIFY

   Verify the chain

   The client walks the chain from the genesis hash to head_hash. If every link matches, the record is internally consistent — the receiver knows the blocks it is about to use are the blocks that were written.

An example handoff

Each block carries prev_hash and curr_hash, so verification is self-contained: a reader needs only the block list.

{
  "schema": "locker.handoff.v1",
  "task_id": "refactor-auth-42",
  "from_agent": "planner",
  "to_agent": "worker",
  "constraints": ["no schema changes", "tests must stay green"],
  "artifacts": [{ "name": "plan.md", "size": 2048 }],
  "budget_usd": 1.25
}

{
  "task_id": "refactor-auth-42",
  "from_agent": "worker",
  "to_agent": "reviewer",
  "status": "completed",
  "canonical_ref": { "repo": "owner/name", "branch": "main", "commit_sha": "…" },
  "verification": { "test_command": "pytest -q", "exit_code": 0, "tests_passed": 12, "tests_failed": 0 },
  "environment": { "runtime": "python 3.11.8", "dependency_manifest": "requirements.txt", "dependency_hash": "sha256:…" }
}

Install and configure

Padlock has two parts. lockermcp is the MCP client your agent talks to; lockerd is the daemon that stores pads. The client is published on PyPI; the daemon you run yourself. Each is a normal Python package.

Three ways to use Padlock — and what each one actually is

1 · The MCP client (published package)

uvx lockermcp runs the client straight from PyPI without installing it. This is the published client command — it is not a standalone hosted service.

uvx lockermcp

2 · Register it with an MCP client

The client's only required configuration is LOCKER_URL — the base URL of the daemon it should talk to.

{
  "mcpServers": {
    "lockermcp": {
      "command": "uvx",
      "args": ["lockermcp"],
      "env": { "LOCKER_URL": "http://127.0.0.1:8000" }
    }
  }
}

3 · Run your own daemon

The daemon binds 127.0.0.1:8000 by default and stores pads in a single SQLite file. Use the same variable, LOCKER_URL, to point the client at it.

uvx --from lockermcp lockerd
# or, in a virtualenv:
pip install lockermcp
LOCKER_DB_PATH=locker.db LOCKER_MODE=open lockerd

Six tools are exposed over stdio: locker_deposit (create + append + seal in one call), locker_create, locker_append, locker_seal, locker_manifest, and locker_read_blocks. Reads verify the chain in Python and return an integrity result — the model never computes a hash itself.

Practical uses

Padlock is a primitive, not a platform. It fits wherever one automated step hands work to another and the receiver benefits from a checkable record.

Padlock does not claim integrations it doesn't have. It speaks MCP over stdio, and the repository README documents how to register it with an MCP client.

Integrity guarantees — and their limits

The chain is a precise tool with a precise scope. It is worth stating both halves plainly.

Inspect a live pad

The hosted daemon seeds a permanent read-only pad, so you can look at a real hash chain without creating anything or paying. It is read-only: writing to it is refused.

curl https://api.padlockspace.org/v1/pads/demo-pad-v1/blocks

Or open the demo endpoint directly. This page does not fetch it in your browser — you can read the raw JSON yourself.

Discuss a paid pilot

Padlock ships as a self-hosted primitive. If you want it wired into a handoff you already run, I take on a small number of fixed-scope integration pilots.