MCP vs A2A vs ACP: Which Integration Do You Need?

Choose the protocol by the boundary you need to cross. MCP connects an AI application to tools and context. A2A supports communication with another agent. ACP needs its full name: Agent Communication Protocol and Agent Client Protocol are different projects.

The Agent Communication Protocol documentation now says that the project is part of A2A. Agent Client Protocol addresses communication between coding agents and editors. Treating all these names as competing enterprise message buses leads to the wrong architecture decision.

This comparison replaces an earlier version containing unsupported release numbers, performance figures, commercial pricing and ownership claims. The recommendations below are based on the linked official documentation and explicit engineering trade-offs. We have not run a comparative latency benchmark.

Start with the integration you need

Choose the boundary first. A protocol name cannot decide who is allowed to act.

MCP: expose capabilities to an AI application

In MCP, the host application coordinates the model and its client connections. Servers expose tools, resources and prompts. The server is not simply the AI model, and initialisation is not a fixed manifest containing every callable operation. Capability negotiation and subsequent discovery are separate concerns. The architecture and tools specifications describe this division.

For an issue-tracker assistant, an MCP server might expose search_issues and get_issue. The host can use these while composing an answer. If you expose an update tool, your application must enforce permissions and any approval requirements before the update reaches the issue tracker.

The linked transport specification defines stdio and Streamable HTTP. SSE can carry streamed server messages within the HTTP transport; it is not a substitute for the client sending its request. Check the selected host and SDK together rather than assuming that supporting MCP means supporting every optional capability.

For protected HTTP integrations, follow the authorisation specification. Receiving a token does not settle whether its holder may read a particular customer record. Keep those checks close to the data access. Our MCP server architecture guide turns this into an implementation and acceptance checklist.

A2A: delegate work across an agent boundary

A2A is useful when the remote party manages how a task is completed. You request an outcome and handle its messages, state and returned artefacts without requiring access to its internal tool definitions. The official A2A and MCP comparison treats the protocols as complementary.

Consider a support assistant asking a specialist diagnostic agent to investigate an incident. Define what information it can send, what constitutes an acceptable result and what happens if the specialist needs clarification. A completed protocol task is still something your application must evaluate: it is not proof that the diagnosis is correct.

The A2A specification defines Agent Cards, task and message structures, and protocol bindings including JSON-RPC, gRPC and HTTP+JSON. An Agent Card describes the agent interface and capabilities. It does not require every deployment to run a distributed registry, nor does it certify that an agent is trustworthy.

Use the authentication mechanisms declared by the service and enforce authorisation at the service boundary. Test task retrieval, cancellation and interrupted communication against the binding and features your counterpart actually implements. Do not assume that a successful initial exchange proves that a long-running workflow can recover after a disconnect.

ACP: spell out which project you mean

Agent Communication Protocol provided a REST-based interface for communicating with agents. Its official welcome page explicitly announces its move into A2A and links to migration guidance. For an existing integration, use that guidance to examine the mapping of runs, messages and state. For a new agent-to-agent integration, evaluate A2A directly instead of treating the older ACP project as a separate future enterprise stack.

Agent Client Protocol standardises the interface between coding agents and editors. Its introduction describes local subprocess communication using JSON-RPC over stdio and remote communication over HTTP or WebSocket. Check the supported transport and features in your chosen editor and agent before deployment. This protocol is relevant when a user wants to operate a coding agent from their editor, including the surrounding interactive experience.

A coding agent can expose an editor-facing interface while using MCP tools internally. An agent accepting delegated work can also use MCP. These combinations describe different integration boundaries; they do not require you to install every protocol in every application.

Test the workflow before choosing a stack

Use a small representative task and a deliberately failing counterpart. For an MCP integration, test whether a denied project read is rejected before data leaves the server. For A2A, interrupt a delegated task and check whether your application can establish its current state without starting duplicate work. For an editor integration, deny a permission request and confirm that the proposed operation does not proceed.

Then test a misleading result. Return a well-formed answer that omits required evidence. Your application should identify the missing evidence even though the protocol exchange succeeded. Record the exact client, server, binding and configuration used for each test so the result can be reproduced after upgrades.

A successful exchange proves the systems communicated. It does not prove the answer is right.

If latency or operating cost determines the choice, measure the complete task in your environment: model work, upstream calls, retries and human approvals included. A bare transport number cannot predict that experience. Use the agent evaluation checklist to define acceptance before building a larger integration.

Source trail

Official documentation reviewed for this repair. Dated MCP specification links identify the edition used; the other links point to their maintained documentation.

• Architecture
• Transports
• Tools
• Authorization
• Specification
• A2A And Mcp
• Welcome
• Introduction