The agent protocol map
Find open-source projects for every agent protocol: A2A agents, ACP editor agents, x402 and AP2 payments, MCP Apps, MCP gateways and mobile agents. Compare them by stars, licence and official status, then build on the one that fits.
A2A (Agent2Agent) is an open standard for communication between AI agents. It covers agent-to-agent interaction, while MCP covers connections from agents to tools. Google originally developed it and donated it to the Linux Foundation.
The Agent Client Protocol (ACP) standardizes communication between code editors and coding agents, much as the Language Server Protocol did for language servers. Local agents run as editor sub-processes using JSON-RPC over stdio, and remote agents use HTTP or WebSocket. It is a different project from the Agent Communication Protocol, which shares the ACP abbreviation.
AP2 (Agent Payments Protocol) is an open protocol for payments made by AI agents. It extends the Agent2Agent protocol and integrates with the Universal Commerce Protocol. The current version supports credit and debit card pull payments, with e-wallets, real-time bank transfers and digital currencies on its roadmap.
x402 is an open standard for internet-native payments built on the HTTP 402 Payment Required status code. A server can require payment for a request, and a client that receives a 402 response pays and retries. Coinbase created the protocol and contributed it to the x402 Foundation at the Linux Foundation, announced on April 2, 2026.
MCP Apps are an extension to the Model Context Protocol that lets servers return interactive HTML interfaces rendered inside the chat. A tool declares a ui:// resource, the host renders it in a sandboxed iframe, and the app talks to the host over JSON-RPC through postMessage. Host support varies by client.
An MCP gateway is a proxy that sits between MCP clients and MCP servers, usually to aggregate servers behind one endpoint, bridge transports or apply access policy. It is a product category and not a protocol of its own. The MCP specification defines hosts, clients and servers, and does not define a gateway role.
Mobile agents are AI agents that run on a phone, control a phone, or act as personal assistants through messaging apps such as WhatsApp and Telegram. They typically read the screen and tap through apps, or connect to devices through tools such as ADB. This is a group of independent projects and not a single protocol.
Star counts and activity checked 2026-11-08. Built on one of these? List it free.
Questions
What is the difference between MCP and the Agent2Agent (A2A) protocol?
MCP connects one agent to its own tools, APIs and data. A2A connects agents to other agents, so one agent can hand work to another. The A2A docs describe an agent that uses MCP to reach a diagnostic tool and A2A to order a part from a supplier's agent.
How do I install an MCP server locally for Claude Code or Cursor?
You tell the client how to start the server. In Claude Code you run claude mcp add with the server's start command, for example claude mcp add airtable -- npx -y airtable-mcp-server. In Cursor you add the same command to an mcp.json file. Our step-by-step install guide covers each client.
Is it safe to install unverified agent skills from GitHub?
Treat a skill like any code you did not write. Its instructions steer your agent and its scripts run on your machine, so read SKILL.md and any scripts first and limit what the agent can reach. On AgenticMart, each listing shows what a tool can touch and its scan report, which helps but does not replace that review.
How does the x402 payment protocol work for AI agents?
A server answers an unpaid request with HTTP 402 and says what payment it accepts. The client pays and retries with a signed payment in a header, and the server verifies and settles it before returning the resource. No account or API key is needed.
Can I list or claim my own open-source repository on AgenticMart for free?
Yes. Listing is free, and so is the automated scan. If your repository is already listed, sign in with GitHub and claim it to edit the listing and start a new scan.
More detail: how to install an MCP server, A2A and x402.