A2A Protocol

Open standard for letting AI agents from different frameworks talk to each other.

Free· Free and open source (Apache 2.0)Agents

Best for

Pick A2A Protocol if you are building multi-agent systems that need to interoperate across frameworks, teams, or vendors without leaking internals.

Skip if

Skip it if you just need a single agent or are looking for a ready-made hosted agent platform rather than a wire protocol to implement.

A2A (Agent2Agent) is an open protocol specification for inter-agent communication, originally developed by Google and donated to the Linux Foundation. It defines how opaque agentic applications, built on LangGraph, CrewAI, custom stacks or proprietary platforms, can delegate tasks, exchange context, and collaborate without exposing their internal memory, tools, or prompts. It sits next to MCP in the stack: where MCP standardises agent-to-tool calls, A2A standardises agent-to-agent calls.

This is infrastructure for developers, not a SaaS. It is most relevant if you are shipping multi-agent systems that need to talk across organisational or framework boundaries, or if you are a platform vendor who wants your agents to be addressable by others. Official SDKs ship in Python, JavaScript, Java, C#/.NET, Go and Rust, and the protocol is Apache 2.0. Governance is run by a Technical Steering Committee with AWS, Cisco, Google, IBM Research, Microsoft, Salesforce, SAP and ServiceNow at the table, which gives it a credible shot at sticking as a default.

There is no pricing because there is no hosted service. The cost is engineering time to implement the spec or integrate one of the SDKs, plus whatever runtime you point it at. Expect the spec, extensions, and SDK surface to keep moving while the standard matures.

Editor's take

A2A is the agent-to-agent counterpart to MCP, and with the Linux Foundation plus most of the hyperscalers behind it, it has a real chance of becoming the default. Treat it as plumbing: valuable if you are shipping agent platforms or multi-vendor agent stacks, overkill if you just need one LangChain bot.

— The AI Tool Bible editorial team

Pros

✅ Backed by Linux Foundation with AWS, Google, Microsoft, IBM and others on the TSC
✅ Official SDKs in Python, JS, Java, .NET, Go and Rust
✅ Cleanly complements MCP rather than competing with it
✅ Apache 2.0, no vendor lock-in or hosted dependency