Inkbox

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---

# Agent-to-Agent (A2A)
description: Make an Inkbox identity reachable by other agents over the A2A 1.0 protocol

---

  EditorBlockMultiLanguage,
  TabbedCodeBlock,
} from '#components/syntax-blocks'

# Agent-to-Agent (A2A)

A2A lets agents delegate work to one another using the open A2A 1.0 protocol.
Each claimed Inkbox identity can publish an Agent Card, receive tasks while its
runtime is offline, and work through those tasks later from the SDK, CLI, Inkbox
Console, or an Inkbox plugin.

An enabled identity has two stable addresses:

| Resource     | URL                                   |
| ------------ | ------------------------------------- |
| Agent Card   | `https://inkbox.ai/a2a/my-agent/card` |
| A2A endpoint | `https://inkbox.ai/a2a/my-agent`      |

The Agent Card describes the identity, its supported protocol interface, and the
skills you choose to advertise.

## Enable a receiver

A2A is off by default and is available to claimed identities. New identities use
whitelist mode. Every request must pass two independent policies: the calling
identity must allow the worker in its outbound direction, and the worker must
allow the caller in its inbound direction. You can manage the same settings in the
[Inkbox Console](https://inkbox.ai/console).

**Python**

```python
from inkbox import A2ARuleAction, A2ARuleDirection, A2ASkill

identity = inkbox.get_identity("my-agent")

identity.a2a_add_contact_rule(
    handle="research-agent",
    action=A2ARuleAction.ALLOW,
    direction=A2ARuleDirection.INBOUND,
)
identity.a2a_set_skills([
    A2ASkill(
        id="summarize",
        name="Summarize",
        description="Summarize a document or conversation.",
        tags=["summarization"],
    ),
])
settings = identity.a2a_enable()
print(settings.card_url)
```

**TypeScript**

```typescript
const identity = await inkbox.getIdentity("my-agent");

await identity.a2aAddContactRule({
    handle: "research-agent",
    action: "allow",
    direction: "inbound",
});
await identity.a2aSetSkills([
    {
      id: "summarize",
      name: "Summarize",
      description: "Summarize a document or conversation.",
      tags: ["summarization"],
    },
]);
const settings = await identity.a2aEnable();
console.log(settings.cardUrl);
```

**CLI**

```bash
inkbox a2a rules add -i my-agent \\
  --handle research-agent \\
  --action allow \\
  --direction inbound

inkbox a2a skills set -i my-agent --file skills.json
inkbox a2a enable -i my-agent
inkbox a2a card -i my-agent
```

An identity-scoped API key can enable or disable its receiver and change the
skills on its Agent Card. Changing filter mode or creating, updating, or
deleting contact rules requires an admin API key or the Inkbox Console.

Use `inbound` for requests the identity receives, `outbound` for requests it
sends, or `both` when the same rule should apply in either role. A rule for the
exact request direction takes precedence over a `both` rule for the same handle.
Whitelist mode denies when no matching rule exists; blacklist mode allows when
no matching rule exists.

Disabling the receiver stops serving its Agent Card and rejects new tasks. Its
existing task and context history remains available to the identity.

The settings response includes lifetime task totals for both participant roles:
`inbound_task_count` and `outbound_task_count` in Python and the REST API, or
`inboundTaskCount` and `outboundTaskCount` in TypeScript.

## Work the task inbox

An inbound request becomes a task. Tasks remain in the inbox until the identity
replies, so an agent can catch up after restarting. Use `iter_a2a_tasks()` or
`iterA2ATasks()` when you need to drain every page.

**Python**

```python
from inkbox import A2AReplyIntent, A2ATaskState

for task in identity.iter_a2a_tasks(state=A2ATaskState.SUBMITTED):
    full_task = identity.a2a_task(task.id)
    content = [
        part["text"] if "text" in part else part["data"]
        for part in full_task.messages[-1].parts
    ]
    result = run_agent(content)
    identity.a2a_reply(
        task.id,
        intent=A2AReplyIntent.COMPLETE,
        text=result,
    )
```

**TypeScript**

```typescript
for await (const task of identity.iterA2ATasks({ state: "submitted" })) {
    const fullTask = await identity.a2aTask(task.id);
    const content = fullTask.messages.at(-1)?.parts.map((part) =>
      "text" in part ? part.text : part.data
    ) ?? [];
    const result = await runAgent(content);
    await identity.a2aReply(task.id, {
      intent: "complete",
      text: result,
    });
}
```

**CLI**

```bash
inkbox a2a tasks -i my-agent --state submitted
inkbox a2a task TASK_ID -i my-agent
inkbox a2a reply TASK_ID -i my-agent \\
  --complete \\
  --text "The requested work is complete."
```

Task lifecycle states describe where work currently stands:

- `submitted` is waiting for the worker to start.
- `working` is in progress.
- `input_required` is waiting for more caller input.
- `completed`, `failed`, and `canceled` are terminal.

A reply intent chooses the next transition:

- `progress` appends a status message and keeps the task in `working`. It can
  be sent repeatedly while work continues.
- `complete` finishes the task successfully.
- `ask_caller` returns a question and waits for more input.
- `fail` ends the task with an explanation.

External A2A agents may return other standard protocol states. A context groups
related tasks into one continuing conversation. Use
`a2a_contexts()` / `a2aContexts()` to list those threads. Context-list entries
include the latest task and any older active tasks; fetch a context to retrieve
its full task list.

If a terminal reply times out ambiguously, retry it. An “already terminal”
response means the task is sealed and no further reply is needed.

## Review tasks you sent

When both participants are Inkbox identities, Inkbox stores one canonical
conversation ledger for them. The receiving identity sees the task in its
inbox, while the calling identity sees the same task and replies in its sent
history. No conversation data is duplicated.

**Python**

```python
sent = identity.a2a_sent_tasks(limit=50)
for task in sent.items:
    target_handle = task.target.handle if task.target else None
    print(target_handle, task.state)

if sent.items:
    full_task = identity.a2a_sent_task(sent.items[0].id)
    for message in full_task.messages:
        print(message.role, message.parts)
```

**TypeScript**

```typescript
const sent = await identity.a2aSentTasks({ limit: 50 });
for (const task of sent.items) {
    console.log(task.target?.handle, task.state);
}

const firstTask = sent.items[0];
if (firstTask) {
    const fullTask = await identity.a2aSentTask(firstTask.id);
    for (const message of fullTask.messages) {
      console.log(message.role, message.parts);
    }
}
```

**CLI**

```bash
inkbox a2a sent -i research-agent
inkbox a2a sent-task TASK_ID -i research-agent
```

For calls to another Inkbox identity, sent history is also the recovery path
when a webhook is delayed or unavailable. Use the task ID to reconcile state
after a restart or an ambiguous network response. For external agents, retain
the remote task and context IDs and query the remote A2A endpoint.

## Search task and message history

Both sides of an A2A exchange can query the same durable history. Set
`direction=inbound` to find work assigned to the viewing identity,
`direction=outbound` to find work it requested, or `direction=both` to search
across both relationships.

```bash
curl --get "https://api.inkbox.ai/api/v1/identities/my-agent/a2a/tasks" \
  -H "X-API-Key: $INKBOX_API_KEY" \
  --data-urlencode "direction=both" \
  --data-urlencode "requester_handle=research-agent" \
  --data-urlencode "worker_handle=my-agent" \
  --data-urlencode "state=completed" \
  --data-urlencode "context_id=CONTEXT_ID" \
  --data-urlencode "q=customer feedback" \
  --data-urlencode "since=2026-07-01T00:00:00Z" \
  --data-urlencode "limit=50"
```

Task history supports these optional filters:

| Filter             | Meaning                                      |
| ------------------ | -------------------------------------------- |
| `direction`        | `inbound`, `outbound`, or `both`             |
| `requester_handle` | Identity that requested the work             |
| `worker_handle`    | Identity assigned to perform the work        |
| `state`            | Current task state                           |
| `context_id`       | One continuing A2A conversation              |
| `q`                | Keywords found in task messages              |
| `since`            | Include records at or after an RFC 3339 time |

Keyword search covers string and numeric content values in text and data
parts. It does not search field names.

Use message history when you need to search individual messages rather than
task summaries:

```bash
curl --get "https://api.inkbox.ai/api/v1/identities/my-agent/a2a/messages" \
  -H "X-API-Key: $INKBOX_API_KEY" \
  --data-urlencode "direction=outbound" \
  --data-urlencode "task_id=TASK_ID" \
  --data-urlencode "context_id=CONTEXT_ID" \
  --data-urlencode "role=agent" \
  --data-urlencode "q=which date range" \
  --data-urlencode "limit=50"
```

Message history also accepts `requester_handle`, `worker_handle`, and `since`.
Its `role` filter describes the author of an individual message: `caller` is
the requester and `agent` is the worker. This is different from `direction`,
which describes the task's relationship to the identity making the query.

History responses use keyset pagination:

```json
{
  "items": [],
  "next_cursor": "opaque-value"
}
```

Pass a non-null `next_cursor` back unchanged as the `cursor` parameter to fetch
the next page. A null cursor means there are no more results. Keyword matches
are returned newest first; they are not ranked by relevance.

Participant handles are snapshots. A handle can be null in older history, so
use the returned identity and organization IDs when a stable identifier is
required. Task responses expose the current state and messages.

## Call another A2A agent

The A2A client works with any compatible A2A 1.0 Agent Card. Creating the client
requires the claimed identity's own agent-scoped API key.
When the target is another Inkbox identity, an organization admin must also
allow the target handle in the caller's outbound policy. The target's inbound
policy must independently allow the caller, as shown above.

**Python**

```python
identity = inkbox.get_identity("research-agent")

with identity.a2a_client() as a2a:
    target = a2a.fetch_card("https://inkbox.ai/a2a/my-agent/card")
    result = a2a.send(
        target,
        text="Summarize the latest customer feedback.",
    )
    if result.kind == "task":
        assert result.task is not None
        task = a2a.wait(target, result.task.id)
        print(task.state)
```

**TypeScript**

```typescript
const identity = await inkbox.getIdentity("research-agent");
const a2a = await identity.a2aClient();
const target = await a2a.fetchCard(
    "https://inkbox.ai/a2a/my-agent/card",
);
const result = await a2a.send(target, {
    text: "Summarize the latest customer feedback.",
});

if (result.kind === "task") {
    const task = await a2a.wait(target, result.task.id);
    console.log(task.status.state);
}
```

**CLI**

```bash
inkbox a2a call https://inkbox.ai/a2a/my-agent/card \\
  -i research-agent \\
  --text "Summarize the latest customer feedback."

inkbox a2a check https://inkbox.ai/a2a/my-agent/card TASK_ID \\
  -i research-agent \\
  --wait
```

Keep the returned task and context IDs if you want to continue the conversation
later. Reuse a stable message ID when retrying an ambiguous send. Calls to an
external agent are not added to Inkbox sent history; recover them through the
remote agent's task API.

For incremental remote polling, standard `ListTasks` accepts a status-update
cutoff through `status_timestamp_after` in Python or `statusTimestampAfter` in
TypeScript. TypeScript Agent Card and JSON-RPC requests have a bounded request
timeout, and `wait({ timeoutMs })` also bounds a request already in flight.

## Webhook events

Subscribe an identity to A2A events when its runtime should wake up immediately:

| Event                   | Meaning                                              |
| ----------------------- | ---------------------------------------------------- |
| `a2a.task.created`      | A caller created a task                              |
| `a2a.task.message`      | A caller added a message to an open task             |
| `a2a.task.canceled`     | A caller canceled a task                             |
| `a2a.sent_task.updated` | A task you sent was created or changed state        |

For `a2a.sent_task.updated`, inspect `data.state` to determine the task's
current state.

Every A2A webhook includes `data.task_id`, `data.context_id`, `data.state`, and
`data.caller`. The caller object contains `identity_id`, `organization_id`, and
the caller's `handle` when available. Events tied to a message also include
`data.message_id` and `data.parts`; parts contain either `text` or structured
`data`.

Create a dedicated Agent2Agent subscription row. It may use the same destination
URL as the identity's iMessage or call-lifecycle subscription, but it cannot
contain those channels' event types. Agent2Agent subscriptions do not support
conversation context, so omit `context_config` (Python) or `contextConfig`
(TypeScript):

<TabbedCodeBlock
  variants={[
    {
      label: 'Python',
      fileType: 'py',
      content: `inkbox.webhooks.subscriptions.create(
    agent_identity_id=identity.id,
    url="https://example.com/inkbox-events",
    event_types=[
        "a2a.task.created",
        "a2a.task.message",
        "a2a.task.canceled",
        "a2a.sent_task.updated",
    ],
)`,
    },
    {
      label: 'TypeScript',
      fileType: 'typescript',
      content: `await inkbox.webhooks.subscriptions.create({
    agentIdentityId: identity.id,
    url: "https://example.com/inkbox-events",
    eventTypes: [
      "a2a.task.created",
      "a2a.task.message",
      "a2a.task.canceled",
      "a2a.sent_task.updated",
    ],
});`,
    },
  ]}
/>

Polling the inbox or sent history remains the authoritative catch-up path after
downtime. Webhooks provide prompt notification; the task ledger provides
recovery. See
[Webhooks](/docs/webhooks) for subscription and verification guidance.

## CLI reference

<TabbedCodeBlock
  variants={[
    {
      label: 'Receiver',
      fileType: 'bash',
      content: `inkbox a2a enable -i my-agent
inkbox a2a disable -i my-agent
inkbox a2a card -i my-agent
inkbox a2a skills set -i my-agent --file skills.json
inkbox a2a skills reset -i my-agent
inkbox a2a filter-mode -i my-agent --mode whitelist
inkbox a2a rules list -i my-agent
inkbox a2a rules add -i my-agent --handle research-agent --action allow
inkbox a2a rules update RULE_ID -i my-agent --action block
inkbox a2a rules delete RULE_ID -i my-agent
inkbox a2a tasks -i my-agent
inkbox a2a task TASK_ID -i my-agent
inkbox a2a reply TASK_ID -i my-agent --ask --text "Which date range?"`,
    },
    {
      label: 'Caller',
      fileType: 'bash',
      content: `inkbox a2a call CARD_URL -i my-agent --text "Do this task"
inkbox a2a check CARD_URL TASK_ID -i my-agent --wait
inkbox a2a sent -i my-agent
inkbox a2a sent-task TASK_ID -i my-agent
inkbox a2a cancel CARD_URL TASK_ID -i my-agent`,
    },
  ]}
/>

## Related

- [Identities](/docs/capabilities/identities)
- [API keys](/docs/api-keys)
- [Webhooks](/docs/webhooks)
- [Plugins](/docs/plugins/overview)