The A2A protocol end to end — Agent Cards and discovery, the task lifecycle, the message/part/artifact content model, transports and methods, streaming and push notifications, security, and how A2A and MCP compose.
Tools are one half of an agent's world and other agents are the other half, and A2A is the open standard that lets agents built by different teams, in different frameworks, discover and delegate to each other as peers.
A2A is the open standard that lets agents built by different teams, in different frameworks, discover and delegate to each other as peers — the agent-to-agent complement to MCP's agent-to-tools.
Before one agent can delegate to another it has to find it and understand what it can do, and in A2A that self-description is a single structured document called the Agent Card.
Before one agent can delegate to another it must find it and understand it. In A2A that self-description is a single structured document — the Agent Card.
Delegating real work between agents is rarely a quick round trip, so A2A makes the task a first-class object with an explicit lifecycle that survives long-running, interruptible, asynchronous collaboration.
Delegated work is rarely a quick round trip, so A2A makes the task a first-class object with an explicit lifecycle that survives long-running, interruptible, asynchronous collaboration.
Agents need to exchange more than plain strings — instructions, files, images, structured data, and finished deliverables — and A2A's content model handles all of it with three composable objects.
Agents exchange more than plain strings — instructions, files, images, structured data, and finished deliverables. A2A's content model handles all of it with three composable objects.
A2A defines what agents exchange independently of how it travels, so the same operations work over JSON-RPC, gRPC, or plain REST — and the operation set is small enough to hold in your head.
A2A defines what agents exchange independently of how it travels, so the same operations work over JSON-RPC, gRPC, or plain REST — and the operation set is small enough to hold in your head.
Long-running agent work needs a way to report progress without the client holding its breath, and A2A offers two: stream the updates live, or register a webhook and get called back.
Long-running agent work needs a way to report progress without the client holding its breath. A2A offers two: stream the updates live over SSE, or register a webhook and get called back.
When agents from different organizations delegate real work to each other, trust cannot be assumed, so A2A builds authentication into the Agent Card and demands it on every request.
When agents from different organizations delegate real work, trust cannot be assumed, so A2A builds authentication into the Agent Card and demands it on every request.
The two protocols people keep pitting against each other are actually two halves of the same architecture — MCP gives an agent its tools, A2A gives it collaborators, and real systems need both.
MCP gives an agent its tools, A2A gives it collaborators, and real systems need both. How the two protocols compose — tools within an agent, agents between — in one architecture.
This series is part of a larger body of work by Pratik Dhanave, an Agentic AI Architect writing about production AI systems, distributed systems, and cloud-native engineering. Explore all course series, browse every post, or find topics via the tag index.