Protocols
Protocols agents actually speak.
Standards worth knowing, and which catalog tools implement them. Adoption is derived from the catalog, never hand-listed.
Model Context Protocol
Anthropic
Tool-side: how an agent reaches capabilities. A2A is how agents reach each other.
100 graded B+ · 121 in catalog
Agent2Agent Protocol
Linux Foundation (originated at Google)
Agent-to-agent: peers delegating work. MCP is how one agent reaches tools.
9 graded B+ · 16 in catalog
Agent Client Protocol
Zed Industries
Editor-side: how an IDE drives an agent. AG-UI is the web front-end equivalent.
10 graded B+ · 12 in catalog
Agent–User Interaction Protocol
CopilotKit
Front-end-side: streaming an agent into a web UI. ACP is the editor equivalent.
1 graded B+ · 1 in catalog
llms.txt
Answer.AI
Content-side: how a site presents itself to agents. Not an API protocol.
0 graded B+ · 0 in catalog
x402
Coinbase
Payments per request. AP2 is the mandate-based purchase protocol.
0 graded B+ · 1 in catalog
Agent Payments Protocol
Mandated purchases across merchants. x402 is per-request micropayment.
0 graded B+ · 0 in catalog