Overview
Formal specification for the Agent Session Protocol v0.1
Status: v0.1 (Draft)
The Agent Session Protocol (ASP) specification defines the message formats, state transitions, error handling, and security guarantees for structured agent-to-agent communication. This document serves as the authoritative reference for implementors.
Notation Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this specification are to be interpreted as described in RFC 2119.
Protocol Version
The current protocol version is asp/0.1. Every ASP message MUST include a version field matching the pattern asp/{major}.{minor}. Implementations MUST reject messages with an unsupported version.
Version negotiation is not currently defined. Both participants in a session MUST use the same protocol version.
Conformance Levels
ASP defines three conformance levels. Implementations MUST declare which level they support in their Agent Card.
Minimal
A Minimal implementation MUST support the following performatives:
| Performative | Purpose |
|---|---|
INFORM | Exchange information and status updates |
QUERY | Request information from other agents |
CLOSE | Terminate a session |
Minimal implementations can exchange information but cannot negotiate or commit to agreements. This level is suitable for read-only agents, monitoring agents, and simple information providers.
Standard
A Standard implementation MUST support all 13 performatives:
PROPOSE, ACCEPT, REJECT, COUNTER, INFORM, QUERY, CLARIFY, COMMIT, DELEGATE, ESCALATE, WITHDRAW, OBSERVE, CLOSE
Standard implementations have full negotiation and commitment support. This is the RECOMMENDED level for production agents that participate in multi-step workflows.
Full
A Full implementation MUST support everything in Standard, plus:
| Capability | Description |
|---|---|
| Trust scoring | Calculate, update, and share trust scores based on session outcomes |
| Economic model | Budget tracking, escrow, transaction ceilings, and breach penalties |
| Multi-party sessions | Sessions with three or more participants, including observer roles |
Full implementations are intended for enterprise deployments where agents transact with economic value and require game-theoretic incentive alignment.
Most agents SHOULD target Standard conformance. The Minimal level exists for simple utility agents, while Full is designed for high-value autonomous transactions.
Specification Documents
Message Schema
Complete JSON schema, per-performative body definitions, and validation rules for all 13 performatives.
Session State Machine
Nine session states, all valid transitions, timeout behavior, and terminal conditions.
Error Codes
Rejection code registry, six error categories, and recommended recovery actions.
Security Model
Eight-threat model, hash chain integrity, DPoP binding, encryption modes, and economic safeguards.
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