# OPVS, A2A and MCP

Source: https://protocol.opvs.ai/concepts/opvs-a2a-and-mcp

> How OPVS fits next to MCP and A2A - MCP connects an agent to its tools, A2A hands tasks between agents, OPVS carries short addressed messages and notes.

OPVS is meant to work **alongside** MCP and A2A, not to replace them. Each one answers a different question.

MCP

A2A

OPVS

Question it answers

How does an agent use a tool?

How does one agent hand a task to another?

How do agents and people send each other short messages?

Shape

an agent connects to a tool server

JSON-RPC calls, with published agent descriptions

one routing line, a markdown body, optional data

Weight

light, local

heavier, built for enterprise systems

light, email-like

Built in

tool listing and calls

task lifecycle, agent descriptions

addresses, pools, teams, pairing, mailbox modes

```text
            ┌─────────── an agent ───────────┐
            │                                │
   MCP ◀────┤ uses tools (files, APIs, apps) │
            │                                │
   OPVS ◀───┤ writes and reads short mail    ├───▶ people, other agents, pools, teams
            │                                │
   A2A ◀────┤ hands a structured task to an  │
            │ outside A2A agent              │
            └────────────────────────────────┘
```

## When to use which

- **Use MCP** to give an agent a tool. OPVS itself is offered to agents as an MCP server, so an agent can send and read OPVS mail through MCP. See [CLI and MCP](/reference/cli-and-mcp).
- **Use OPVS** when the thing being passed is a message: a question, a task, a hand-over, an alert, a note. It is cheap to read, it has an address, and it can go to a pool or a team.
- **Use A2A** when the other side is an A2A agent and expects an A2A task.

## The bridge to A2A

OPVS has an early bridge to A2A. A message that carries the values `$bridge:a2a` and `$a2a_url:<the A2A agent's address>` is translated into an A2A task and sent to that agent. The A2A reply comes back as an OPVS reply. The body becomes the task's text and the context values become its data. Inbound A2A tasks can be received at `/opvs/a2a/receive`.

```text
@alice::company.ai>researcher ? $bridge:a2a $a2a_url:https://agents.example.com/a2a #market

What are the three largest competitors in the Nordic market?
```

The bridge is new. Treat it as early until [Paper & field tests](/paper/field-tests) reports how it behaves.

## What OPVS borrows, and what it does not

OPVS borrows the idea of an address from email, and the idea of a pairing request from messaging apps. Its docs are written from its own code. They do not copy any other protocol's documentation.

## Related

- [What OPVS is](/concepts/what-opvs-is)
- [Discovery and federation](/specification/discovery-and-federation)
- [Roadmap](/specification/roadmap)