> ## Documentation Index
> Fetch the complete documentation index at: https://docs.algovoi.co.uk/llms.txt
> Use this file to discover all available pages before exploring further.

# A2A (Agent2Agent Protocol)

> Google's open protocol for AI agents to discover and call each other. AlgoVoi runs a live, payment gated A2A agent issuing offline verifiable attestations.

## What is A2A

[Agent2Agent (A2A)](https://a2aproject.github.io/A2A) is Google's open protocol for AI agents from different vendors and frameworks to communicate. Each agent publishes an **Agent Card** at `/.well-known/agent.json` describing its capabilities, endpoints, and auth requirements. Clients discover the card, send a `Task`, and receive `Artifacts` back.

AlgoVoi runs a live A2A v1.0 agent at [`api.algovoi.co.uk/.well-known/agent.json`](https://api.algovoi.co.uk/.well-known/agent.json) with three skills, and is listed on the [A2A protocol partners page](https://a2a-protocol.org/latest/partners/) among the organisations building and adopting A2A.

## Verifiable receipts for A2A

Every payment-gated A2A task AlgoVoi handles produces a deterministic, offline-verifiable receipt on
the shared [JCS canonicalisation substrate](/canonicalisation-substrate): a categorical ALLOW / REFER
/ DENY [compliance receipt](/compliance-receipt) at admission and an A2A settlement attestation
on-chain, bound by the [`action_ref`](/canonicalisation-substrate) primitive. Anyone can recompute the
canonical bytes and verify the signature years later with the open [receipt verifier](/receipt-verifier),
with no live call to AlgoVoi and no customer PII.

See [Agentic Payment Receipts](/agentic-payment-receipts) for how this works across x402, AP2, A2A and
MPP.

## When to use A2A

<CardGroup cols={2}>
  <Card title="Cross-framework agents">
    Your LangGraph agent calling someone's CrewAI agent, with no SDK lock-in.
  </Card>

  <Card title="Discoverable services">
    AI agents finding payment-gate services via Agent Card registries.
  </Card>

  <Card title="x402 over A2A">
    Wrap an x402-paywalled endpoint in an A2A task. Agents pay through the same protocol they discover with.
  </Card>

  <Card title="Long-running tasks">
    A2A handles streaming and push notifications natively, which fits multi-step agent workflows.
  </Card>
</CardGroup>

## AlgoVoi's A2A skills

The live agent card publishes three skills you can call from any A2A-compatible client.

### `verify-payment`

Verify any on-chain transaction across the 7 supported chains. Input: `tx_id`, `chain`. Output: verification status plus the extracted amount, asset, and sender.

### `create-checkout`

Request a hosted-checkout link without going through the dashboard. Input: `amount`, `currency`, `preferred_network`. Output: checkout URL and token.

<Note>
  `create-checkout` takes a fiat amount and currency, not chain microunits. AlgoVoi's price oracle does the conversion. This is by design. Agents shouldn't have to know per-chain decimals.
</Note>

### `check-status`

Poll a checkout link's status. Input: `token`. Output: `active`, `paid`, `expired`, or `cancelled`, plus `tx_id` when paid.

## Quickstart

### From an A2A client

```typescript theme={null}
import { A2AClient } from "@a2a-protocol/sdk-js";

const client = new A2AClient("https://api.algovoi.co.uk");
const card = await client.fetchAgentCard();

const task = await client.sendTask({
  message: {
    parts: [{ kind: "text", text: "verify tx ABCD1234… on algorand:mainnet" }]
  },
  skill: "verify-payment"
});

console.log(task.status, task.artifacts);
```

### From an MCP-bridged agent

A2A and MCP can co-exist. See the [A2A MCP bridge](https://github.com/GongRzhe/A2A-MCP-Server). AlgoVoi's skills can be exposed to Claude, Cursor, or any MCP-aware agent through the bridge.

## First-mover position

As of 2026-04-22, AlgoVoi is **the only live A2A agent in the crypto-payments ecosystem**. A probe of 22 candidate domains found zero other deployed payment-gate agents. The Agent Card is published for any AI agent or registry to discover.

## Production gateway only

A2A skills run on the `api.algovoi.co.uk` gateway, not on the cloud edge. They need direct facilitator and database access. Cloud endpoints proxy normal payment traffic, not A2A skills.

## See also

* [AP2](/protocols/ap2) typically rides on A2A as its transport
* [x402](/protocols/x402) is used as the payment leg inside A2A skills
* The [A2A spec](https://a2aproject.github.io/A2A)
* AlgoVoi's [agent card](https://api.algovoi.co.uk/.well-known/agent.json) (live JSON)