arcaeon

One MCP connector for the whole Arcaeon toolbox. Install once, wire one stanza into your client, get eleven tools: a tamper-evident agent ledger, a static checker for MCP-server source, and the hosted witness that catches truncation.

Free to install. Free to use, except the two tools that spend money on our side, and those tell you the price in plain English instead of failing.

Arcaeon ships a shelf of small single-purpose packages. A shelf is a distribution problem: an agent that would use three of them has to find three, install three, and wire three stanzas. Most never get past the first. This is the one door.

Install

pip install arcaeon

Today that command does not work yet, and this README is not going to pretend otherwise. The connector depends on arcaeon-ledger>=0.7.0 and arcaeon-mcp-vet>=0.0.8; PyPI currently has arcaeon-ledger 0.5.9 and no mcp-vet at all. Until both are published, install the two from source first:

pip install -e path/to/arcaeon-ledger      # 0.7.0 — the agent tools live here
pip install -e path/to/mcp_vet             # 0.0.7
pip install -e path/to/arcaeon_connector   # this package

The dependency pins are declared honestly rather than loosened to whatever PyPI happens to hold: a >=0.5.9 that installs and then fails at import is worse than a resolver error that says what is missing.

Check the install without starting a server:

arcaeon-mcp --tools

Wire it into a client

.mcp.json (Claude Code and friends):

{
  "mcpServers": {
    "arcaeon": {
      "command": "arcaeon-mcp",
      "args": ["--log", "agent.log.jsonl"],
      "env": {}
    }
  }
}

With the paid lane switched on, and the ledger somewhere deliberate:

{
  "mcpServers": {
    "arcaeon": {
      "command": "arcaeon-mcp",
      "args": ["--log", "state/agent.log.jsonl", "--ns-dir", "state/ledgers"],
      "env": {
        "ARCAEON_KEY": "your-witness-key"
      }
    }
  }
}

If your client cannot run console scripts, "command": "python", "args": ["-m", "arcaeon_connector"] is the same server.

The tools

Names are prefixed by which product answers: ledger_*, vet_*, witness_*.

The paid lane

Two tools need ARCAEON_KEY, because a hosted pin is a commit somebody pays for. Called without a key they return a plain sentence:

witness_pin is a paid Arcaeon tool and no ARCAEON_KEY is set, so nothing was sent.

It pins your ledger head with the hosted witness (https://witness.arcaeon.io): a
party you cannot advance, which is the only thing that catches truncation.

Free tier: 100 pins/month, no card. To get one: email hello@arcaeon.io or ask
Nora for a key.
Entry pack: $5 for 1,000 pins ($0.005/pin): https://buy.stripe.com/aFa4gAb10ead3xy35f0RG08
...

No stack trace, no silent nothing, and the free door named before the paid one — the witness free tier is 100 pins/month with no card, and the witness library itself is self-hostable free forever (point ARCAEON_WITNESS_URL at your own deployment and the same two tools work). The catalog those numbers come from is /.well-known/offers.json, and a test in this repo fails if the copy in the code drifts from it.

Environment

The optional license gate (off by default)

A second, optional gate sits in front of the same two paid tools and answers a different question: not "does this caller have a witness account" (that is ARCAEON_KEY) but "is this copy of the package licensed". It is inert unless you set LICENSE_GATE_REQUIRED=1 - unset, nothing here imports, nothing here runs, and the connector behaves exactly as it did before this existed.

When it is on, the license is bound to the ledger namespace being pinned. That is the whole idea: a borrowed key would have to pin under the lender's namespace, into the lender's public pin history, under the lender's name. The gate does not prevent that; it makes it self-incriminating, which for people who buy audit tooling is the part that bites.

It fails closed. LICENSE_GATE_REQUIRED=1 with no gate module installed refuses the paid tools rather than waving them through, because a required check that passes because its own implementation is missing looks enforced and is nothing.

Honest limit, stated here as well as in the gate's own README: a client-side license check deters, it does not prevent. Anyone who can edit the package can delete the call. The real moat is updates and the ledger identity, not this.

What this does NOT prove

Inherited from the packages it bundles, restated here because a bundle that drops the caveats is selling a stronger claim than its parts:

• Tamper-evidence is not truth. The ledger proves a record was not altered. It says nothing about whether what it records was correct, or whether the agent that wrote it was honest at the time.
• A clean vet_scan is not "safe". It means a small set of documented failure classes found nothing. mcp-vet publishes its own blind spots inside every grade, including one it demonstrates on its own server.
• A pin proves no-truncation only relative to what the witness saw, and only as recently as the last pin. The pin gap is the security parameter.
• Witness auth is bearer-key only (auth_level: "bearer-stage0"). A leaked key can pin and renew in your name. Owner-signature auth is designed (STAGE1_SIGNATURE_DESIGN) and not built.
• This connector adds no analysis of its own. It re-exports; the ledger tools dispatch straight into arcaeon_ledger.mcp_server.handle, the same function the standalone server runs. If a result here disagrees with the standalone server, that is a bug in this package, and one of the tests exists to catch exactly that shape of drift.

Run the tests

pip install -e ".[dev]"
pytest -q

Fifteen tests. Every one drives a real MCP round-trip; one of them spawns the installed entry point as a subprocess and speaks raw JSON-RPC down the pipe, because "one install and it works" is a claim about the package, not about an importable module.

Security note

Local stdio only. The tools read caller-named paths, so do not put this behind a network transport without an auth layer in front — which is what vet_scan's own zero-auth check would tell you about anyone else's server.

MIT licensed. Every product Arcaeon charges for is listed in /.well-known/offers.json; a charge that is not in that file is not ours.