Power your agent
The publisher's own command. Not a PlugMCP endpoint.
Host a copy with our keys and logs.
uvx arcaeon==0.10.0Claude Code has no install link for a local command. Copy the command below and run it in a terminal.
ARCAEON_KEY=<secret> claude mcp add io.arcaeon-arcaeon -- uvx arcaeon==0.10.0Run in a terminal.
{ "mcpServers": { "io.arcaeon-arcaeon": { "command": "uvx", "args": [ "arcaeon==0.10.0" ], "env": { "ARCAEON_KEY": "<secret>" } } }}claude_desktop_config.json
Remote URL or a command on your machine? How the two installs differ
Run on PlugMCP
A new server you create. It is not this listing's official endpoint. Use the publisher install when you want their URL and their credentials.
LaunchFrom the publisher
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: .
A record of what an agent did that the agent cannot quietly rewrite, and a way for anyone to check.
arcaeon <verb>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]"
Other ways in, same package:
pipx install "arcaeon[mcp]"
pipx keeps arcaeon in a space of its own, apart from your other Python
packages, and still puts arcaeon on your path.
uvx arcaeon demo
uvx (from uv) runs it once without keeping an install: the demo logs two
rows, changes one word and shows the BROKEN line.
py -m pip install --user arcaeon
On Windows, when pip is not found, the py launcher that comes with Python
installs it for your user alone, no administrator needed.
Log two rows, check them, change one word of history, check again. The lines
run as typed in PowerShell, cmd and a POSIX shell. --field KEY=VALUE builds
the row for you, so there is no JSON to quote; that matters on Windows, where
PowerShell 5.1 strips the inner double quotes from a JSON argument like
'{"tool": "search"}' before arcaeon ever sees it.
$ arcaeon log agent.jsonl --field tool=search --field query=weather
<the new row's chain value>
$ arcaeon log agent.jsonl --field tool=send_email --field 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.
Three families. The full reference, with usage lines and examples, is docs/VERBS.md.
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.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.distill: cut a tool's output to a token budget and record what was cut.dedup: drop near-copies from a list of texts.meter: per-key usage counts and monthly caps for your own tools.stamp, credits, buy: the hosted door (below).mcp: the MCP server (below).selftest: run every bundled self-check.version: print the version of the package and each part.stamp, pin --remote, seal and credits talk to the hosted witness at
witness.arcaeon.io, over HTTPS, and only when you run them. buy reads the
offers file bundled with the package and makes no request.
arcaeon stamp FILE: sends the file's sha256 and size, never its bytes.
Works without a key, inside a free daily allowance.arcaeon pin LEDGER --ns NAME --remote: records your ledger's head with
the hosted witness. Needs ARCAEON_KEY.arcaeon seal PATH: grades an MCP server,
then seals the report. Needs ARCAEON_KEY and nothing else, and uses one
credit. The witness's pin is the seal: it records your ledger's head and
checks no signature from your machine. With the arcaeon[sign] extra and a
signing key in MCP_VET_RECEIPT_KEY the report is also signed and the seal
says SIGNED; on the base install it says UNSIGNED and is sealed all the
same. Without ARCAEON_KEY nothing is sent, you still get the free badge,
and it exits 3. A key pins only under its own namespace prefix; you do not
need to know yours. If the default namespace is refused, seal reads your
prefix from the refusal (no credit spent) and pins under
<prefix>-sealed-scans. --ns still picks one yourself.arcaeon credits: shows your balance. Needs ARCAEON_KEY. Looking is free.arcaeon buy: prints a checkout link. It opens nothing and takes no card.
Payment happens on Stripe's page.ARCAEON_KEY is the one setting. Treat it like a password: a leaked key can
pin in your name. For plans and prices, see arcaeon.io/pricing.
pip install "arcaeon[mcp]"
arcaeon mcp
arcaeon mcp starts the MCP server on stdio. It gives an agent the ledger,
vet and witness tools. arcaeon mcp --tools lists them without starting
anything; it needs the [mcp] extra too (on the base install it prints the
pip install 'arcaeon[mcp]' hint and exits 2).
A note for MCP registry listings: before 0.9, uvx arcaeon started this
server. It still does for 30 days after this release, when there is no verb
and stdin is not a terminal. Point your client at arcaeon mcp now. The
fallback is removed in 1.0.0.
One table for every verb. What each word means, in two sentences apiece, is in docs/WORDS.md.
3 is never a pass. A gate that treats only 0 as green fails on it, which is the point.
Many logs, one summary: keep the three counts side by side. Any summary arcaeon prints over many logs shows how many were VERIFIED, how many BROKEN and how many COULD NOT LOOK, never one rate. "98% verified" hides whether the other 2% were broken or simply never read, and those call for very different Monday mornings. If you build your own dashboard on the exit codes, keep the three columns too.
Before 0.9 some old tools used other codes for the same words (reconcile used
2 for COULD NOT LOOK, for example). For the 0.9.x releases, --legacy-exit on
a verb returns the old tool's own code, so a gate wired to it keeps working
while you rewire it. The flag goes away in 1.0.0. MIGRATION.md lists every
code that moved.
The short version, before the detail:
arcaeon proxy writes carries args_digest for the request
and result_digest for the response. Given the bytes, you can check they
are the ones that crossed the seam; you cannot re-run the call to get them.What a hash chain proves: the rows were not changed in place after they were
written. An edit, a deletion or a reorder in the middle breaks every later
link, and verify names the first broken line.
What it does not prove:
What a pin proves: the log was not cut short or rewritten relative to what the witness saw, and only as of the last pin. The longest gap between pins is your real exposure. A pin file you keep yourself shows the mechanism works; it is not an outside party. The hosted witness uses a bearer key, not a signature.
What reconcile proves, in its own words:
vet and badge report what their own checks found in the bytes they read.
They are not a review by a person and not a safety certification.
Writing is not fast. Each log row (Ledger.append) is flushed and synced to
disk before the next one starts, which costs about 18 ms a row on an ordinary
laptop disk: 102,000 rows took about 22 minutes to write. Reading is fast (the
same 50 MB log verifies in about 2.5 seconds).
arcaeon deal records a purchase made by an agent. The buyer's agent and the
seller each write the same steps (mandate, commit, pay, ship, deliver, cancel)
on their own ledger. Either side, or anyone they hand both files to, can line
them up with arcaeon deal dispute and get one verdict: MATCHED, MISSING,
ALTERED or COULD NOT LOOK. The steps and a worked example are in
docs/DEAL.md.
Before 0.9 this was thirteen packages: arcaeon-ledger, arcaeon-adapter,
arcaeon-receipt, arcaeon-audit, arcaeon-mcp-vet, arcaeon-once,
arcaeon-compact, arcaeon-continuity, arcaeon-baseline, arcaeon-dedup,
arcaeon-distill, arcaeon-meter and arcaeon-all. Each old name gets one
last release that installs arcaeon and keeps the old import and the old
command working, with a warning that names the new import. Nothing breaks the
day you upgrade. MIGRATION.md has the old and new import and
command for each name, and which exit codes changed.
shims/README.md explains how the old names forward.
MIT. See LICENSE.
© 2026 MCP Directory.
A record of what an agent did that the agent cannot quietly rewrite, and a way for anyone to check.
{ "mcpServers": { "io.arcaeon-arcaeon": { "command": "uvx", "args": [ "arcaeon==0.10.0" ], "env": { "ARCAEON_KEY": "<secret>" } } }}Tools
No tool list yet. Remote servers get one after the first health check.
FAQ
Copy the stdio config for Cursor, Claude Desktop, Claude Code, or VS Code on this page. It uses the publisher's install, not a PlugMCP proxy.
The publisher lists these environment variables: ARCAEON_KEY.
Arcaeon runs locally over stdio.
Last checked 2026-11-14. A record of what an agent did that the agent cannot quietly rewrite, and a way for anyone to check.