Arcaeon MCP server

arcaeon

<!-- mcp-name: io.arcaeon/arcaeon -->

A record of what an agent did that the agent cannot quietly rewrite, and a way for anyone who doubts it to check.

Every row your agent writes is hash-chained to the row before it. Change a row, delete one, or swap two, and the check names the line where the chain breaks. Hand the file to someone else and they can run the same check without asking you for anything.

One package. One command: arcaeon .

Install

pip install arcaeon

Python 3.10 or newer. The base install has zero dependencies. That means pip pulls in arcaeon and nothing else: no protocol SDK, no crypto library, no parser. Everything in the Record, Prove and Save lists below runs on the Python standard library. It also means no network on import. The hosted verbs open a connection when you run them, and so do a few options that say so: proxy --pin-witness, and receipt cite, which looks each citation up online. Everything else works offline.

The heavy parts are extras. Add only what you use:

pip install "arcaeon[mcp]"

A 60-second first run

Log two rows, check them, change one word of history, check again. These are POSIX shell lines (on Windows, use Git Bash or WSL, or adjust the quotes).

$ arcaeon log agent.jsonl '{"tool": "search", "query": "weather"}'
<the new row's chain value>
$ arcaeon log agent.jsonl '{"tool": "send_email", "to": "ops"}'
<the new row's chain value>
$ arcaeon verify agent.jsonl
{
 "verdict": "VERIFIED",
 "ok": true,
 "rows": 2,
...
(exit 0)
$ python -c "import pathlib; p = pathlib.Path('agent.jsonl'); p.write_text(p.read_text().replace('weather', 'sunshine'))"
$ arcaeon verify agent.jsonl
{
 "verdict": "BROKEN",
 "ok": false,
...
 "first_break": "line 1: chain mismatch",
...
(exit 1)

That is the whole idea. The edit was one word in the first row, and the check found it and named the line. Exit 0 means VERIFIED. Exit 1 means BROKEN. A CI gate can use the exit code alone.

What it did not catch: someone deleting the last rows. See Limits below, and arcaeon pin, which is the fix.

The verbs

Three families. The full reference, with usage lines and examples, is docs/VERBS.md.

Record: write down what happened

• log: add one JSON row to a ledger.
• verify: check a ledger's chain. VERIFIED, BROKEN or COULD NOT LOOK.
• receipt: issue or check a portable receipt someone else can verify.
• once: prove a side effect (a refund, an email) ran once, not twice.
• proxy: sit in front of an MCP server and record every tool call.
• pin: hand a ledger's current head to a witness, a local file or the hosted one.
• deal: a purchase recorded on both sides, step by step.

Prove: check what was written

• reconcile: line up two tapes of the same calls. MATCHED, MISSING, ALTERED or COULD NOT LOOK.
• audit: check a log, pin its head, or export it as one bundle.
• vet: read an MCP server's source and grade it. No code runs.
• badge: a free Markdown badge and JSON report for an MCP server.
• seal: the same badge, sealed by the hosted witness. Paid.
• baseline: score a fixed probe set before a change and again after.
• compact: check a receipt that says what a context compaction dropped.

Save: spend fewer tokens

Shortened. The full README is on GitHub.