Introduction
What ASP is, and how it relates to ACP, MCP, and USL
Agent Session Protocol (ASP) is the storage and migration protocol for agent sessions — the session-layer counterpart to ACP.
| protocol | owns | timeline |
|---|---|---|
| ACP (Agent Client Protocol) | editor↔agent live control | present |
| MCP (Model Context Protocol) | agent↔tool invocation | present |
| ASP | session persistence, replay, cross-runtime migration | past |
ACP handles the live present; ASP handles the durable past. ASP answers one question: how to collect any agent runtime's session log into a unified, recoverable, inter-convertible storage layer, so that resume / fork / handoff across harnesses and unified history rendering become possible.
What ASP defines
- The canonical session schema (envelope, 27 event types, content blocks).
- Event semantics (entity revisions, authority/confidence, lineage DAG).
- The fidelity matrix (declared per-axis preservation, never silent loss).
- Opaque-payload conventions (unparseable bytes round-trip verbatim).
Repositories
agent-session-protocol/asp— the protocol spec (canonical schema + docs).agent-session-protocol/universal-session-log— USL, the storage-first reference implementation.
Where to start
- Session model — how sessions, runs, turns, and lineage are modeled.
- Content blocks — the content taxonomy and opaque passthrough.
- Fidelity — how conversion fidelity is declared.
- ACP & MCP — how ASP relates to the rest of the ecosystem.
- USL implementation — quick start for the reference implementation.