What is A2A?
A2A, short for Agent2Agent, is an open protocol that lets independent AI agents built on different frameworks, languages, or vendors discover each other, exchange messages, and coordinate tasks without exposing their internals.
Also written: Agent2Agent, Agent2Agent protocol, A2A protocol
Explained
A2A is an open standard for communication between agent systems that may be opaque to one another. According to its specification, agents collaborate through declared capabilities and exchanged messages, and they do not have to share internal state, memory, or tools.
The protocol has a small set of core concepts. An Agent Card is a JSON document describing an agent's identity, skills, endpoint, and authentication needs. A Task is the unit of work, with a unique ID and a lifecycle of defined states. A Message is one turn from a user or an agent, made of Parts, and a Part can be text, a file reference, or structured data. An Artifact is an output of a task, also made of Parts.
Operations include sending a message, streaming a message, getting, listing, and cancelling tasks, subscribing to a task, and managing push notification settings. The specification defines bindings over JSON-RPC, gRPC, and HTTP with JSON, and keeps one data model across them. Streaming reuses Server-Sent Events, and long-running work can notify a client-registered webhook or be polled.
At the time of checking (2026-10-26) the page listed 1.0.0 as the latest released version.
Primary source
Agent2Agent (A2A) Protocol Specification (a2a-protocol.org), read Oct 26, 2026
This entry paraphrases the page above. Sources change; check it for the current wording.
Listings that use this
The 5 top-ranked listings tagged for A2A. Rank weighs adoption, freshness, documentation and publisher identity; how we rank and grade. Money never changes the order.
- 0.689score
GPT Researcher
GPT Researcher
Open-source research agent that plans questions, searches the web or your documents in parallel and writes a cited report with any LLM.
AgentAFreshness: A★ 30.3K↓ 8.5K/wk - 0.453score
402cron
402cron
Scheduled HTTP delivery for autonomous agents.
AgentCFreshness: C - 0.453score
402post
402post
Classified listings for AI agents: publish a listing over HTTP or MCP, pay with x402 (USDC on Base), and read listings as web pages, Markdown, JSON and RSS.
AgentCFreshness: C - 0.453score
402registry
402registry
A paid check of whether AI crawlers can actually see a website: a plain HTTP fetch with no JavaScript, the way GPTBot, ClaudeBot and PerplexityBot fetch pages.
AgentCFreshness: C - 0.453score
POPCORN Witness (767-2676)
Briarwood
Witness layer for agents: signed receipts binding a SHA-256 digest of exact bytes to a witnessed time interval.
AgentCFreshness: C
Related
Cite this page
What is A2A?. Agent Mart. https://agentmart.dev/glossary/a2a (last updated 2026-10-26)
Written Oct 26, 2026, updated Oct 26, 2026. All glossary terms