Protocol Specification

Abstract

The Agent Interoperability Session Protocol (AISP) defines a lightweight, transport-agnostic standard for identity, communication, memory sharing, delegation, and consent between software agents — including but not limited to large-language-model (LLM) powered AI agents.

AISP is designed to complement, not replace, existing tool-calling protocols such as MCP. Where MCP governs how an agent calls tools exposed by an external server, AISP governs how two peer agents discover, trust, and collaborate with each other across session boundaries.

The protocol is layered. A minimal L0 implementation uses only the local filesystem. Full L3 implementations use a Hub server with WebSocket streaming, cryptographic signing, and fine-grained consent grants.

Design Principles

Terminology

Session Identity

Every session is identified by a 26-character ULID (Universally Unique Lexicographically Sortable Identifier) prefixed with sess_. The ID is generated at session creation time and persists for the lifetime of the session.

At L2 and above, each session generates an Ed25519 keypair on first start. The public key is published in the session manifest. All outbound messages are signed with the private key; receivers verify the signature before processing.

{
  "id": "sess_01HX9J2N3PQRSTVWXYZ",
  "name": "my-agent",
  "kind": "interactive",
  "realm": "default",
  "created_at": "2026-04-06T09:00:00Z",
  "public_key": "ed25519:MCowBQYDK2VwAyEA...",
  "capabilities": [
    "memory.read",
    "memory.write",
    "delegate.receive"
  ],
  "transport": "file://~/.aisp/realms/default"
}

Message Format

Every AISP message is a JSON object conforming to the Envelope schema. The envelope is transport-agnostic and must not be modified by intermediate hubs or proxies.

{
  "aisp": "0.1",
  "id": "msg_01HX9J2N3PQRSTVWXYZ",
  "from": "sess_01HX9J2N3PQRSTVWXYZ",
  "to": "sess_02HX9J2N3PQRSTVWXYZ",
  "realm": "default",
  "sent_at": "2026-04-06T09:01:00Z",
  "ttl": 300,
  "category": "delegate",
  "payload": {
    "task": "summarize",
    "input": {
      "file": "README.md"
    }
  },
  "signature": "base64url:..."
}

Protocol Categories

AISP defines seven message categories. Each category has a defined payload schema. Hubs route messages based on category to enable selective subscription and filtering.

{
  "kind": "interactive",
  "capabilities": [
    "memory.read",
    "delegate.receive"
  ]
}

{
  "nonce": "abc123",
  "timestamp": "2026-04-06T09:01:00Z"
}

{
  "op": "set",
  "key": "project.name",
  "value": "My Project",
  "scope": "realm"
}

{
  "task": "summarize",
  "input": {
    "file": "README.md"
  },
  "deadline": "2026-04-06T10:00:00Z"
}

{
  "delegate_id": "msg_01HX...",
  "status": "success",
  "output": {
    "summary": "A README."
  }
}

{
  "capability": "memory.read",
  "namespace": "project.*",
  "expires_at": "2026-04-07T00:00:00Z"
}

{
  "type": "task.completed",
  "data": {
    "task_id": "msg_01HX...",
    "duration_ms": 1240
  }
}

Security Model

AISP's security model is built on three pillars: cryptographic identity, explicit consent grants, and scope-limited capabilities.

Transport Bindings

Compliance Levels

AISP defines four compliance levels. Each level is a superset of the previous.

Extension Mechanism

Implementations may add custom message categories using the x- prefix (e.g., x-myorg-task). Extension categories must not conflict with the seven core categories and must not be required for base compliance.

Extension payload schemas should be published at a stable URL and referenced in the ext field of the envelope:

{
  "aisp": "0.1",
  "id": "msg_01HX...",
  "from": "sess_01HX...",
  "to": "sess_02HX...",
  "realm": "default",
  "sent_at": "2026-04-06T09:01:00Z",
  "category": "x-myorg-task",
  "ext": "https://schema.myorg.com/aisp/x-task/v1",
  "payload": {
    "type": "image-generation",
    "prompt": "A purple circuit board"
  }
}

Receivers that do not understand an extension category MUST NOT reject the envelope; they SHOULD log a warning and forward the message if they are acting as a hub.