# Protocol versions (/docs/concepts/protocol-versions)



Every wrapper speaks **A2A v1.0 natively** and is **backward compatible with v0.3.x clients** out of the box. There is nothing to configure. The behaviour is built on the official `@a2a-js/sdk`'s own v0.3 compatibility layer, not a hand-written shim, and lives only in `@a2a-wrapper/core`.

## How negotiation works [#how-negotiation-works]

Per request:

**Agent card.** `GET /.well-known/agent-card.json` reads the caller's `A2A-Version` header.

| Header                  | Response                                                                                    |
| ----------------------- | ------------------------------------------------------------------------------------------- |
| `1.0`                   | The native v1.0 card, using `supportedInterfaces[]`                                         |
| `0.3`, `0.3.0`, or none | A v0.3-shaped legacy card with `url`, `additionalInterfaces` and `protocolVersion: "0.3.0"` |

**JSON-RPC.** `POST /a2a/jsonrpc` accepts native v1.0 shapes and translates v0.3 requests and responses. Legacy method names such as `message/send` and `message/stream` keep working.

**REST.** The routes under `/a2a/rest` accept v1.0 shapes; legacy routes such as `/a2a/rest/v1/message:send` keep working.

No separately configured v0.3 server is needed.

## Which version should my client use? [#which-version-should-my-client-use]

* New clients should send `A2A-Version: 1.0`.
* Existing v0.3 clients need no changes. The examples in these docs use the v0.3 method names (`message/send`) because they work with every client.

## The protocolVersion config field [#the-protocolversion-config-field]

Example configs set `"protocolVersion": "0.3.0"` in `agentCard`. This is informational: it does not limit which wire format is served, because that is negotiated per request.

## Signed cards [#signed-cards]

v1.0 supports JWS-signed agent cards as an opt-in. See [agent cards](/docs/concepts/agent-cards#signed-agent-cards).