ALTWEB Context Loader MCP server

ALTWEB — signed context capsules

Signed context capsules for AI agents — Markdown compiled into self-contained, verifiable, optionally encrypted artifacts + an MCP loader that refuses unsigned or untrusted context. Verify before you inject.

AI agents run on plain-text context: instructions, personas, skills, memory files. None of it has provenance — anything that can write those files can poison them. ALTWEB gives context a chain of custody, and makes the loader refuse anything that lacks one:

content compressed (deflate), optionally encrypted (AES-256-GCM), optionally signed (ECDSA P-256). Self-contained — opens in any browser, verifies offline, needs no server: you hand someone a file, not a database.

• Capsule — markdown compiled into a single .altweb.html file (or URL):

into your agent only when the signature is valid and the signer's public key is in your trust file. Unsigned, tampered, or untrusted capsules are refused at load time, with an explicit reason. Refusal is the default: an empty trust file rejects everything, signed or not.

• Verified context loading — the altweb-context MCP server loads a capsule

you write MD ──► altweb compile --sign ──► capsule (.altweb.html / URL)
                                              │
agent asks for context ──► altweb-context ──► verify signature + trust
                                              │
                              trusted ──► markdown injected
                          everything else ──► REFUSED (reason)

Packages

Quickstart

Both tools are on npm — nothing to clone. Run these commands outside a source checkout (inside this repository, npm resolves the local workspace package):

# create your signing identity (deterministic from a passphrase; only the
# public key + fingerprint are stored, in ~/.altweb/identity.json)
npx altweb keygen --save

# write, compile, sign
echo "# My agent's operating notes" > notes.md
npx altweb compile notes.md -o notes.altweb.html --sign

# verify anywhere, offline
npx altweb verify notes.altweb.html

Wire the loader into an MCP client (Claude Code example):

claude mcp add altweb-context -- npx -y altweb-context

(From source: npm install && npm run build, then use the bundles under packages/*/dist/.)

Running from source

Node.js 20 or newer is required. From the repository root:

npm install
npm run build

# Create and save an identity with the locally built CLI
npm run keygen

# Start the editor in development mode
npm run dev

The editor prints its local URL (normally http://localhost:5173). The CLI can be invoked as node packages/cli/dist/altweb.mjs . Do not use npx altweb inside the checkout: npm may select the local workspace package, whose executable does not exist until it has been built.

The documentation site is intentionally a separate npm project rather than a workspace. To run it locally:

npm install --prefix site
npm run dev --prefix site

Trust a signer by adding its full public key to ~/.altweb/trusted-keys.json (the UNTRUSTED_KEY refusal message hands you the ready-made entry; the short fingerprint is a human label, not the trust anchor):

{ "keys": [ { "name": "Me", "publicKey": "<base64url SPKI>", "fingerprint": "ab:12:..." } ] }

Shortened. The full README is on GitHub.