Agent to agent

Agents talking to agents now has an open standard. It is called A2A, Agent2Agent.

Google started it. Now it lives at the Linux Foundation, and a committee from AWS, Cisco, Google, IBM, Microsoft, Salesforce, SAP and ServiceNow steers it. The current version is 1.0. The specification, the guides and the libraries are at a2a-protocol.org.

This is good news. In document 005 we found no door between agents on one laptop. Between companies, A2A is the first door that many of them agree on.

What A2A gives

Agent card. Each agent publishes a JSON card at /.well-known/agent-card.json: name, skills, address, how to sign in.
Message. One turn of the talk. It holds text, JSON data or a file.
Task. Work with a state: working, needs input, needs sign-in, done, failed.
Artifact. The result of a task: a document, an image, a table.

All of it runs over plain HTTP. One agent stays a black box for the other: its memory and its tools stay hidden. This is the "ask, don't open" rule from document 003. The authors draw the line like this: MCP connects an agent to its tools, A2A connects an agent to another agent.

Fig. 10 — What A2A carries, and the four slots it leaves open.

Where it stops

A2A carries the message well. Four questions from our earlier documents are still open.

The book. A card lives on a domain. You find an agent only if you already know where it lives. The specification says there is no standard API for agent catalogs yet. This is document 002.
The passport. Identity is checked at the HTTP level, with OAuth and TLS. A card can be signed, but it does not have to be. Nothing says whom an agent acts for, what it may do, or how to revoke it. This is document 006.
The meaning. A message is text or JSON. Whether both sides read it the same way is not the job of the protocol. This is document 004.
The door on one laptop. In October 2026 A2A got a command-line tool. It can wrap any script as an agent on localhost. Its authors say it is for demos and tests. Coding agent sessions are still not agents you can call. This is document 005.

A2A has a sample extension called Secure Passport. It carries the caller's ID and a signed piece of context, like a preferred currency. It does not carry a principal, a mandate, limits or a way to revoke. Same word, different job.

What it means for us

We don't need another road. A2A is a good one, and many companies drive on it. But a road does not say where to go, who is driving, or what the cargo means.

The road is built. The book, the passports and the language are not.