HDTP Gateway

The problem

Two people each have an assistant. Today those assistants cannot talk to each other unless both people chose the same product — and then that product sits in the middle of every word.

The fix is not another chat app. It is what email already proved: everyone runs their own endpoint, and addresses are portable. HDTP is that idea for agents, and hdtp-gateway is the endpoint you run.

graph LR
    AA["Alice's agent"] -->|"owner MCP<br/>bearer token"| AN["Alice's node"]
    AN -->|"mTLS + sealed envelope"| BN["Bob's node"]
    BN -->|"owner MCP"| BA["Bob's agent"]
    AN -.->|"vCard: endpoint + key"| BN

No server in that picture has to be trusted by both parties. Bob’s node decides what Alice’s agent may do, Alice’s decides what Bob’s may do, and each holds its own keys.

What makes it different

• You are a keypair, not an account. Your identity is the SHA-256 of your public key. Nothing to sign up for, no username, no provider to be locked out of.
• Every capability is an MCP tool behind a per-contact switchboard. A close friend can book time. A stranger who redeemed a one-time invite can send one message and discover nothing else — tools/list is filtered per caller.
• Sealed end to end. Payloads are HPKE-sealed and signed, so tunnels and edges carry ciphertext. They learn which key a message is for and when — never who sent it, and never what it says.
• It works from behind CGNAT. Direct, Tailscale, frp, ngrok, Cloudflare, or your own domain. With no inbound path at all you need one of those tunnels — or a host: there is no store-and-forward relay, because one would see every sender, recipient and timestamp for its trouble (HDTP §9).
• One binary, SQLite by default. No cluster, no broker, no queue. Postgres when you want it.

What a contact actually is

A vCard — the format your phone already understands, plus two fields. Sharing your agent’s address is sharing a contact.

X-HDTP-CERT is one certificate — the leaf your own root issued this host — and it carries everything: where to reach you, the key to seal to, the fingerprint of the root that is your identity, and how long it is good for. What a contact pins is that root, never the host’s key, which is what lets you change hosts without changing who you are. X-HDTP-SEAL says whether to seal. That is the whole address book.