MCP and A2A answer different integration questions

MCP and A2A answer different integration questions. Model Context Protocol (MCP) standardizes how an AI application connects to tools, resources, and prompts. Agent2Agent (A2A) standardizes how an agent delegates a task to another agent, discovers its capabilities, and receives progress or final artifacts. A system can use one, both, or neither; choosing both only makes sense when it has both kinds of boundary.

The distinction is more useful than comparing transport names. A2A version 1.0 supports JSON-RPC, gRPC, and HTTP+JSON bindings, while MCP’s specification defines its own client-server primitives and transport rules. Shared use of JSON-like messages does not make the protocols substitutes. (MCP basic specification; A2A 1.0 specification)

Choose MCP for tools and data an application controls

Use MCP when a host application or an agent needs a standardized way to discover and invoke a database query, ticketing action, repository operation, search service, or governed data resource. The MCP model is client and server: a client connects to a server that advertises capabilities such as tools, resources, and prompts. The application still decides which servers are available and which invocations it permits.

MCP’s architecture documentation describes the host, client, and server roles as well as tools, resources, and prompts as core primitives. MCP is a strong fit when the value is in controlled access to capabilities. (MCP architecture overview)

Need	MCP fit
Let an IDE agent read issues or create a pull request	Good fit if the repository service is exposed as a governed tool
Give an assistant access to an internal knowledge system	Good fit if retrieval and authorization are enforced by the server
Let a model choose from a limited set of business actions	Good fit if action arguments, scopes, and approvals are checked outside the model
Coordinate an independent specialist that owns a multi-step workflow	Usually an A2A concern instead

The protocol does not turn a tool into a safe action. A tool description can be misleading, retrieved content can contain prompt injection, and a valid credential can still be over-scoped. For HTTP-based transports, MCP’s current authorization specification calls for OAuth 2.1 protections, protected-resource metadata, authorization-server discovery, and audience binding. (MCP authorization specification)

Choose A2A for an agent that owns a task

Use A2A when the remote system is not merely a callable tool. An A2A agent publishes an Agent Card describing its capabilities and interfaces; a client can send a task, receive asynchronous status updates or artifacts, and manage task lifecycle operations such as retrieval or cancellation. The protocol is designed for independent, potentially opaque agent systems, not for exposing the other agent’s internal tools or memory. (A2A 1.0 specification)

That is useful when a procurement agent, research agent, fulfillment system, or another organizational service has its own policies, long-running work, and result contract. The calling agent does not need to know how the specialist performs the work. It needs a stable capability statement, task contract, authentication boundary, completion state, and auditable result.

Need	A2A fit
Hand a research request to a service that returns an evidence bundle later	Good fit
Request a domain agent to prepare an approval-ready purchase order	Good fit when the agent owns the workflow and result contract
Call one deterministic API operation and use its response immediately	Usually MCP or a conventional API is simpler
Share a model’s private chain of thought or unrestricted credentials	Not an A2A purpose

A2A’s specification includes Agent Cards, tasks, streaming, push notifications, security schemes, and in-task authorization. These mechanisms make interoperability possible; they do not replace organization-level identity, policy, approval, logging, or data-classification controls. (A2A 1.0 specification)

Use both only at different layers

The common combined design is straightforward: an A2A specialist agent owns a task, while that specialist uses MCP servers to obtain permitted tools and data. For example, a company can delegate “prepare a vendor-risk review” to a remote risk agent over A2A. That agent can use MCP connections to a sanctioned document store and policy checker. The caller sees an A2A task and result; the specialist enforces its own tool permissions.

This layered approach is useful only if each boundary has a clear owner:

Layer	Owner should decide	Evidence to retain
A2A caller to agent	Which agent can receive which task and data	Agent identity, request, approval, result, task status
Agent to MCP server	Which tools and resources the agent may invoke	User or workload identity, scope, invocation, result, policy decision
Tool to downstream system	Whether the action is actually authorized	Application audit trail, transaction ID, rollback or review status

Do not use A2A merely because an application has several prompts. Do not use MCP merely because an autonomous system calls a tool. A conventional API with a typed request and a service account can be the lower-risk choice for a deterministic integration. For a concrete look at local tool boundaries, start with the local-host trust model in agent frameworks. For framework support, verify the current implementation rather than assuming that CrewAI, AutoGen and LangGraph.

A deployment checklist

Before adopting either protocol, answer these questions in writing:

What identity crosses the boundary: a human user, a workload, an application, or a delegated agent?
What data classifications may cross it, and what must be redacted?
What actions are read-only, what actions require approval, and what actions are forbidden?
How are capabilities discovered and allowlisted rather than accepted from arbitrary endpoints?
Which scopes expire, how are credentials rotated, and how is a compromised integration revoked?
What logs tie a human request to agent delegation, tool invocation, and final side effect?
How does the system stop or recover a long-running task?

If the answer is primarily “give an application governed access to services,” start with MCP. If it is “delegate a discrete outcome to another autonomous service,” evaluate A2A. If the system truly needs both, adopt them one layer at a time and test authorization failures before relying on the happy path.