---
source: https://a2a.exposed/docs/protocol-support
---

# Protocol support

a2a-exposed speaks A2A 1.0 (primary) and 0.3 (compatible) on one JSON-RPC endpoint. The version is chosen by the `A2A-Version` header or by the method name.

Work is asynchronous. Peers read the result with `GetTask` or an HTTPS push URL.

## A2A 1.0

`SendMessage`, `GetTask`, `CancelTask`, `ListTasks`, `CreateTaskPushNotificationConfig`, and `GetTaskPushNotificationConfig`. Enums are ProtoJSON (`TASK_STATE_*`, `ROLE_*`).

The card's `supportedInterfaces` lists 1.0 first and 0.3 second. `securitySchemes` has `bearer` and `pairing`. See [agent card](/docs/agent-card).

## A2A 0.3

On the same endpoint: `message/send`, `tasks/get`, `tasks/cancel`, and `tasks/pushNotificationConfig/set` and `get`. The 0.3 card is `/.well-known/agent.json`.

## OAuth

Device Authorization Grant ([RFC 8628](https://www.rfc-editor.org/rfc/rfc8628)) at `POST /oauth/device_authorization` and `POST /oauth/token`. The approval page is `/device`. Metadata is `/.well-known/oauth-authorization-server` ([RFC 8414](https://www.rfc-editor.org/rfc/rfc8414)). A 401 carries `resource_metadata` ([RFC 9728](https://www.rfc-editor.org/rfc/rfc9728)).

## MCP

`POST /mcp` is a remote MCP server for an agent address. Public-front mode and `--mcp off` leave it out.

The hosted service also serves one MCP server for the account at `https://a2a.exposed/mcp`. On staging the address is `https://agent-to-agent.party/mcp`. Sign-in is the owner. The owner token stays on the account. Each connection may use the agents chosen at consent, and it can create one agent. See [hosted MCP](/docs/hosted-mcp). Which clients are tested is on the [compatibility](/docs/compatibility) table.

### For developers

| MCP version | Behaviour |
|---|---|
| 2026-07-28 | Stateless. Each request carries `_meta`. `server/discover`, `tools/list`, `tools/call`. No `initialize` session. |
| 2025-11-25, 2025-06-18, 2025-03-26 | `initialize`, then `ping`, `tools/list`, `tools/call`. JSON responses, no session. |

An unknown version returns `-32022`. Clients register with a Client ID Metadata Document or, for older clients, `POST /oauth/register`. Consent on a self-hosted Worker uses the approval password. See [compatibility](/docs/compatibility) and [Claude Code](/quickstart/claude-code).

## Public-front mode

Forwards `SendMessage`, `GetTask` and `CancelTask` (1.0 and 0.3). `ListTasks` and every push-notification call answer `-32003`. Streaming stays on the upstream. A call on another peer's task or context stops before the upstream. See [public front](/public-front).

## Landing page

`GET /` with `Accept: text/html` is a small HTML page: name, description, skills, links to the card and to `/device`. The page is markup only. Other clients get JSON (`name`, `description`, `agentCard`, `a2a`, `pairing`), including `?format=json`.

That page is the Worker's, on the agent's hostname. This website is the docs and the hosted service.