Tool: A2A (Agent-to-Agent)

Interact with any A2A-compatible AI agent over the standardized Agent-to-Agent protocol. Use this integration to delegate tasks, poll their status, receive structured artifacts, and wire up webhook callbacks — all from inside a Zelaxy workflow.

Overview

Property	Value
Type	`a2a`
Category	Tool — AI Agents
Auth	API Key (optional, passed per-request)

Operations

Operation	Tool ID	Description
Send Message	`a2a_send_message`	Send a message to an external A2A-compatible agent and receive its response, task ID, and any output artifacts
Get Task	`a2a_get_task`	Query the current status, state, and artifacts of an existing A2A task by ID
Cancel Task	`a2a_cancel_task`	Cancel a running A2A task and confirm whether cancellation succeeded
Get Agent Card	`a2a_get_agent_card`	Fetch the discovery document (Agent Card) for an A2A agent to inspect its capabilities and skills
Resubscribe	`a2a_resubscribe`	Reconnect to a streaming A2A task to retrieve new updates since the last poll
Set Push Notification	`a2a_set_push_notification`	Register a webhook URL to receive push notifications whenever an A2A task changes state

Configuration

Setting	Type	Required	Description
`agentUrl`	`string`	Yes (all operations)	The base endpoint URL of the remote A2A agent (e.g. `https://agent.example.com`)
`message`	`string`	Yes — `a2a_send_message`	The text message to deliver to the agent
`taskId`	`string`	Yes — `a2a_get_task`, `a2a_cancel_task`, `a2a_set_push_notification`, `a2a_resubscribe`	ID of the task to act on
`contextId`	`string`	No	Context ID for conversation continuity across multiple messages
`data`	`string`	No	Structured data to include with the message as a JSON string
`files`	`array`	No	Files to attach to the message (each item: `type`, `data`, `name`, `mime`)
`historyLength`	`number`	No — `a2a_get_task`	Number of conversation history messages to include in the response
`webhookUrl`	`string`	Yes — `a2a_set_push_notification`	HTTPS URL to receive task-state change notifications
`token`	`string`	No — `a2a_set_push_notification`	Authentication token included in outgoing webhook requests for validation
`apiKey`	`string`	No (all operations)	Secret. API key sent to the remote agent for authentication. Use `{{A2A_API_KEY}}` to reference an environment secret

Outputs

The fields returned depend on the operation selected.

Send Message (`a2a_send_message`)

Field	Type	Description
`content`	`string`	Text response content returned by the agent
`taskId`	`string`	Unique identifier of the created or continued task
`contextId`	`string`	Groups related tasks and messages for conversation continuity
`state`	`string`	Task lifecycle state: `working`, `completed`, `failed`, `canceled`, `rejected`, `input_required`, or `auth_required`
`artifacts`	`array`	Output artifacts produced by the agent (array of objects)
`history`	`array`	Conversation history (array of Message objects)

Get Task (`a2a_get_task`)

Field	Type	Description
`taskId`	`string`	Unique task identifier
`contextId`	`string`	Context group identifier
`state`	`string`	Current lifecycle state of the task
`artifacts`	`array`	Task output artifacts
`history`	`array`	Conversation history up to `historyLength` messages

Cancel Task (`a2a_cancel_task`)

Field	Type	Description
`cancelled`	`boolean`	Whether the cancellation was accepted by the agent
`state`	`string`	Task state after the cancellation attempt

Get Agent Card (`a2a_get_agent_card`)

Field	Type	Description
`name`	`string`	Agent display name
`description`	`string`	Agent purpose and capabilities summary
`url`	`string`	Service endpoint URL from the Agent Card
`provider`	`object`	Creator organization details (`name`, optional `url`)
`capabilities`	`object`	Feature support matrix (`streaming`, `pushNotifications`, `extendedAgentCard`)
`skills`	`array`	Available operations exposed by the agent
`version`	`string`	A2A protocol version supported by the agent
`defaultInputModes`	`array`	Default input content types accepted by the agent
`defaultOutputModes`	`array`	Default output content types produced by the agent

Resubscribe (`a2a_resubscribe`)

Field	Type	Description
`taskId`	`string`	Task identifier
`contextId`	`string`	Context group identifier
`state`	`string`	Current lifecycle state
`isRunning`	`boolean`	Whether the task is still executing
`artifacts`	`array`	Task output artifacts accumulated so far
`history`	`array`	Conversation history

Set Push Notification (`a2a_set_push_notification`)

Field	Type	Description
`url`	`string`	The registered HTTPS webhook URL
`token`	`string`	Authentication token for validating incoming webhook requests
`success`	`boolean`	Whether the push notification subscription was registered successfully

Example

[Starter] → [A2A: Send Message] → [Agent: Summarize result]

Trigger the workflow with a user prompt stored in {{starter.input}}. Pass it to the A2A block with agentUrl set to https://research-agent.example.com and apiKey set to {{A2A_API_KEY}}. The a2a_send_message tool returns a taskId and content; feed {{a2a.content}} to a downstream Agent block that summarizes and formats the result for the end user.

Tips

Discover before you send. Run a2a_get_agent_card first to inspect an agent's capabilities and skills. If capabilities.streaming is false, the agent responds synchronously and you will receive content immediately on a2a_send_message.
Long-running tasks. If state comes back as working, use a2a_get_task (poll with a Wait block) or a2a_set_push_notification to receive an async callback when the task reaches completed or failed.
Continue conversations. Pass {{a2a.taskId}} and {{a2a.contextId}} back as taskId and contextId in a subsequent a2a_send_message call to continue the same conversational thread rather than starting a fresh task.
Auth is per-request. The apiKey is forwarded directly to the remote agent; store it as a Zelaxy environment secret and reference it as {{A2A_API_KEY}} rather than hard-coding it in the block config.
Graceful cancellation. Always check cancelled in the a2a_cancel_task output — some agents reject cancellation for tasks in terminal states (completed, failed), and the final state field tells you where the task actually ended up.

A2A (Agent-to-Agent)

Overview

Operations

Configuration

Outputs

Send Message (a2a_send_message)

Get Task (a2a_get_task)

Cancel Task (a2a_cancel_task)

Get Agent Card (a2a_get_agent_card)

Resubscribe (a2a_resubscribe)

Set Push Notification (a2a_set_push_notification)