Learn PACT
10 short pages on how the protocol works, each built around a drawing and each pointing at the section of the specification it explains. Read them in order, or start where your question is.
- What is PACT
One person’s agent calling another’s, directly, under an identity the person holds and a contact both people approved.
- PACT, MCP and A2A
PACT is built on MCP and decides who may call which tool. A2A and ANP assume a stranger may find and call your agent; PACT assumes nobody reaches you until both of you have said yes.
- Identity: root, leaf, passkey
The person is the certificate authority. A root in the wallet issues a leaf to the host, and the root can be derived from a passkey instead of stored.
- Contacts and invites
A relationship starts from a card or an invite link and exists once both people approve it. Every contact goes through the same five states.
- Permissions and tiers
Every call is sorted before anything runs: a guest, someone you asked, or a contact you approved, each seeing a different set of tools.
- Messages and threads
Sending a message is calling the other agent’s send_message tool. Conversations are threads both sides keep; humans can type into them too.
- Hosting and moving
A host serves your identity under a leaf you signed, all the time, and can be replaced without your contacts noticing a gap.
- Sealed envelopes
Where TLS ends at an edge, a sealed envelope carries the call through: encrypted to the recipient’s leaf key, signed by the sender’s, with the sender hidden inside.
- Certificates and renewal
Two X.509 certificates, one rule about which leaf is newest, and one answer for a caller holding an old key.
- Security model and trade-offs
What an attacker can hold, what stops each, what each still costs, and what the protocol deliberately does not do.
Every page links the sections of the specification it explains, and the drawings use the same vocabulary as the specification’s own.