The useful question is not which protocol wins. It is what you want to connect and where responsibility for the work should sit. Start with the interaction you need, then inspect the capabilities of a particular implementation.
MCP and A2A can appear in the same system. Capifold keeps their labels separate so that a tool endpoint is not mistaken for an interchangeable agent service. You can browse MCP servers and A2A agents independently.
When you need a tool connection
MCP gives an application a standard way to connect to servers exposing capabilities such as tools and resources. The host can discover available operations and the inputs those operations expect. See the MCP architecture overview.
Imagine an assistant preparing a repository report. It needs to read open issues, retrieve a file and inspect recent changes. You may want the assistant to retain responsibility for choosing those steps and composing the report. A suitable tool connection can expose the operations it needs.
The word “suitable” matters. A protocol label does not establish repository access, result completeness or whether a write operation is available. Those details belong to the provider's tool and permission contract.
When you need another agent
A2A standardises communication between agents. Its official documentation describes discovery and collaboration across agent boundaries, including task and information exchange. MCP and A2A are described as complementary in the A2A comparison.
In the repository-report example, a separate specialist service might own the review process: it accepts a review request, asks for missing context and returns an assessment. Before choosing it, establish what responsibility you delegate. Does it only propose changes, or can it apply them? How do you retrieve the result, detect failure and cancel work?
These are design questions for your application. Do not assume that every service labelled A2A exposes identical skills or supports every optional feature.
Use the boundary to choose a starting point
Ask yourself what the calling application needs to know. If it needs individual operations with defined inputs, inspect tool interfaces. If it needs to coordinate with a separately operated agent, inspect that agent's collaboration contract. This is a selection aid rather than a claim that either protocol can do only one kind of work.
A single product may expose both. For example, a specialist agent may use tools internally while presenting an agent interface to another team. You still need to evaluate the public interface you will actually connect to. Internal architecture is not permission to invoke other services.
Compare implementations with the same questions
Use a short comparison sheet:
| Question | What to record |
|---|---|
| Capability | The declared operation or skill that matches your task |
| Input and output | Supported formats and the result you expect |
| Connection | Endpoint, transport and compatible protocol version |
| Access | Account, credentials and required permissions |
| Lifecycle | Completion, failure, timeout and cancellation behaviour |
| Evidence | Source, inspected version and any scoped test result |
If a field is absent, leave it unknown. A more detailed description may improve your understanding, but it is not equivalent to a functional test. Follow the evidence guide to keep the distinction clear.
Where Capifold fits
Capifold helps you discover candidates and inspect their descriptions, source manifests and available evidence. It does not make an imported MCP tool into an A2A agent or automatically run either one. The next step is to review the provider contract and prepare a connection you understand.
For a tool candidate, use the MCP selection checklist. To let your own agent search Capifold's index, follow Connect your agent; that connection searches the catalog rather than executing the offers it finds.