Arcaeon: one package for your AI

Which one are you?

Pick the line that fits you. Each path is a few short steps, and each step tells you what you should see when it worked.

Already use a terminal? Skip to install.

• I use an AI coding agent or assistant
• I write Python
• I write JavaScript
• I just want to check a record someone sent me

Four words you will meet

Terminal

A window where you type a command, press Enter, and the computer types its answer back. On Windows, press the Windows key, type PowerShell and press Enter. On a Mac, press Command and Space together, type Terminal and press Return.

pip

The installer that comes with Python: you give it a package name and it downloads and sets up that package for you.

npm

The installer that comes with Node.js for JavaScript packages. Arcaeon installs with pip, not npm.

MCP server

A small program that hands your AI app a set of extra tools. Arcaeon's MCP server starts with arcaeon mcp.

I use an AI coding agent or assistant

1. Open a terminal as described above, and you should see a window with a blinking cursor.
2. Check that you have Python 3.10 or newer. On a Mac, type python3 --version and you should see 3.10 or a higher number. On Windows, open the Start menu, type Python, and read the version in the name of the app that appears. If there is no Python, or it is below 3.10, install Python 3.10 or newer from python.org. On Windows, tick "Add python.exe to PATH" in the installer. Then open a new terminal.
3. Type pip install "arcaeon[mcp]" and press Enter, and you should see a line that starts with Successfully installed.
4. If you saw that pip was not found, type py -m pip install "arcaeon[mcp]" on Windows or python3 -m pip install "arcaeon[mcp]" on a Mac, and if that is not found either, install Python 3.10 or newer from python.org and start again.
5. Type arcaeon mcp --tools and press Enter, and you should see the list of Arcaeon's tools, with nothing started. If you see that arcaeon was not found, close the terminal, open a new one, and try again. If it is still not found, email hello@arcaeon.io.
6. Find your AI app in the table further down this page and open the file it names. Make a copy of the file first. If the file is empty or does not exist, paste the whole block the table shows. If the file already has "mcpServers" ("servers" for VS Code), add only the "arcaeon" entry just before the last closing brace of the "mcpServers" block (of the "servers" block for VS Code), with a comma after the entry before it. If that block is empty, no comma is needed. If the file has text but no "mcpServers" (no "servers" for VS Code), add a comma after the last entry in the file, then the "mcpServers" line ("servers" for VS Code) and everything under it to its closing brace, just before the file's last closing brace. If the file holds nothing but its two braces, no comma is needed. Here is a file with one other server, before and after:

   {
     "mcpServers": {
       "other": {
         "command": "other"
       }
     }
   }

   {
     "mcpServers": {
       "other": {
         "command": "other"
       },
       "arcaeon": {
         "command": "arcaeon",
         "args": [
           "mcp"
         ]
       }
     }
   }

   Save the file and restart the app, and you should see arcaeon among the app's tools. If the app reports a settings error, put your copy back in place of the file, and the app is as it was.
7. Ask your AI to call arcaeon_status, and you should see it name the versions and which tools are free.

I write Python

1. Open a terminal as described above, and you should see a window with a blinking cursor.
2. Arcaeon needs Python 3.10 or newer. On a Mac, type python3 --version and you should see 3.10 or a higher number. On Windows, open the Start menu, type Python, and read the version in the name of the app that appears. If there is no Python, or it is below 3.10, install Python 3.10 or newer from python.org, then open a new terminal.
3. Type pip install arcaeon and press Enter, and you should see a line that starts with Successfully installed.
4. If you saw that pip was not found, type py -m pip install arcaeon on Windows or python3 -m pip install arcaeon on a Mac, and if that is not found either, install Python 3.10 or newer from python.org and start again.
5. Type arcaeon version and press Enter, and you should see a version number for the package and for each part inside it. If you see that arcaeon was not found, close the terminal, open a new one, and try again. If it is still not found, email hello@arcaeon.io.
6. Type arcaeon demo and press Enter, and you should see VERIFIED, then one word changed, then BROKEN with the line that changed.

In your own code, start with from arcaeon.record.ledger import Ledger, as shown on How it works.

I write JavaScript

1. Install Arcaeon once with the Python steps, and you should see a version number when you type arcaeon version.
2. From your JavaScript code, run the arcaeon command as a child process, for example arcaeon verify agent.jsonl, and you should see exit code 0 for good, 1 for a bad finding, 2 for bad usage and 3 for COULD NOT LOOK.
3. To check a witness pin with a plain web request, fetch the public verify address shown on /proves, and you should see a JSON answer whose witnessed field is true, false or null. A 503 or 409 with a named reason is also COULD NOT LOOK.

I just want to check a record someone sent me

Nothing to install. Your browser does the check.

1. If you were sent a receipt file, open arcaeon.io/verify-receipt, and you should see a place to paste or drop it.
2. Drop the receipt in, and you should see VERIFIED, BROKEN or COULD NOT LOOK, with nothing uploaded anywhere.
3. If you were sent a stamp link that starts with arcaeon.io/r/, open it, and you should see the file's fingerprint and the time it was recorded.
4. On that page, pick your own copy of the file under Check your copy of the file, and you should see whether it matches, with nothing sent anywhere.
5. If you were sent a log file instead, that check runs on a computer: follow the Python steps, then type arcaeon verify and the file's name, and you should see VERIFIED, BROKEN with the first broken line, or COULD NOT LOOK.

Nothing to install: use the tools page.

Stamp a file or verify a receipt, in your browser.

Open the tools

What is inside: three families, one package

Every verb runs as arcaeon <verb>, and every verb uses one exit-code table: 0 good, 1 a bad finding, 2 bad usage, 3 COULD NOT LOOK.

Also in the box: selftest runs every bundled self-check, each one planting the failure it exists to catch. What each part proves, and what it does not, is on /proves.

Reconcile two records

Reconcile lines up two records of the same calls, the agent side's and the tool side's, and says where they stop agreeing. It runs on your own machine.

1. Install Arcaeon with the Python steps, and you should see a version number when you type arcaeon version.
2. Type arcaeon reconcile A B with your two record files in place of A and B, and you should see MATCHED, MISSING, ALTERED or COULD NOT LOOK.

MATCHED between two records one party wrote is consistency, not independence.

The hosted door: what needs a key

Everything above runs on your machine with no account. Four verbs talk to the hosted witness at witness.arcaeon.io, over HTTPS, and only when you run them. One more only prints a link.

Treat ARCAEON_KEY like a password: a leaked key can pin in your name. Plans and prices live on one page.

What it costs

Used the old package names?

Before this release Arcaeon was thirteen separate packages. 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. The page for people who installed them has the old and new import and command for each name, and which exit codes moved.

Old names, new commands

If you are an agent, this site has a wing built for you.

If you're an agent, this site has a whole wing for you: the agent side, with every product with an honest status, verbatim review receipts (including the critical ones), the asked→shipped record, and the commands to verify each claim on your own machine. Machine-readable surfaces: /llms.txt (map), /llms-full.txt (everything, one file), /ai.md (agent page as markdown), and /.well-known/offers.json, the single source of truth for what is purchasable.

Don't want to take any of that on faith? Verify us before you talk to us: a real, downloadable evidence bundle (hash-chained log + compaction receipt + a pin from our hosted witness) with the exact commands and quoted outputs to check it yourself.