Live demo capsule

This site publishes a real signed capsule — a small agent persona, compiled and signed with the public ALTWEB demo key. Nothing about it is mocked: the file below is the artifact exactly as the CLI produced it, and every step on this page can be reproduced on your machine.

Download demo.altweb.html →Open it in the browser

Make your own

This capsule was written and signed in the visual editor — no install, all in the browser. Open the editor → to create and sign your own, then verify it exactly like the steps below.

Artifact	/demo/demo.altweb.html
Signer	ALTWEB demo key
Fingerprint	aa:7f:6d:ca:a2:48:08:db
Content	A minimal “release engineer” agent persona in markdown

Verify it locally (CLI)

Download the artifact, then:

curl -fsSL https://altweb.software/demo/demo.altweb.html -o demo.altweb.html
node packages/cli/dist/altweb.mjs verify demo.altweb.html

Expected: the signature reports VALID with fingerprint aa:7f:6d:ca:a2:48:08:db, and the exit code is 0. Now open the file, change any single character of the embedded hash, and run verify again — it fails. That is the entire pitch in one experiment.

To read the content:

node packages/cli/dist/altweb.mjs decode demo.altweb.html

Load it through the MCP server

1. Trust the demo fingerprint by adding it to ~/.altweb/trusted-keys.json:

   {
     "keys": [
       {
         "name": "ALTWEB demo key",
         "publicKey": "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEd2n93TgVGERaW8lTFAEnbjLOUJktbp9ILJnA5XWZIG9qw-RcG19zdm7qFuKCW2Bn7dxvkzPVlI6M07kMmkeQsg",
         "fingerprint": "aa:7f:6d:ca:a2:48:08:db"
       }
     ]
   }

2. With altweb-context registered in your MCP client (setup), ask your agent to call load_capsule with the file path (or this page’s artifact URL) as source. The markdown is returned prefixed with the verified signer line.

3. Remove the entry from the trust file and call load_capsule again: REFUSED (UNTRUSTED_KEY) — the signature is still valid, but the policy no longer allows the signer. Verification and trust are separate on purpose.

The honest caveat

The demo key exists so this page can publish a working example. Its passphrase is public (altweb-demo-capsule) — which means anyone can sign capsules as the demo key. Trust it in your file only while experimenting, then remove it. A fingerprint whose passphrase is public proves integrity, but identifies nobody — which is exactly why your real trust file should contain only fingerprints whose passphrases are actually secret.