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Register and use external agents in Agent Platform using the A2A (Agent-to-Agent) protocol. This enables cross-service agent invocation over standard HTTP — including agents owned by external organizations — supporting delegation, sub-task handoff, and multi-agent orchestration across service boundaries. The routing executor handles remote handoffs transparently, making agent calls location-agnostic: external agents are invoked the same way as local ones.

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Register an External Agent

Register an external agent to make it available within the Agent Platform. Prerequisites
  • The external agent supports the A2A protocol.
  • The agent endpoint is reachable over HTTP or HTTPS.
  • You have the endpoint URL for the external agent.
  • Authentication details are available if required.
To register an external agent:
  1. Navigate to External Agents.
  2. Click Register Agent.
  3. Enter the required details:
    • Agent Name — Name of the external agent.
    • Endpoint URL — URL of the external agent endpoint.
    • Protocol — Communication protocol for the external agent. Supported protocols:
      • A2A
      • REST
    • Authentication Type — Authentication mechanism required by the external agent endpoint. Supported types:
      • API Key
      • Bearer Token
  4. Click Register.
The platform validates the endpoint and adds the agent to the External Agents list. Use the Test Connection action to verify that the endpoint is reachable. On success, the platform fetches and stores the agent card, which defines the agent’s capabilities, skills, and streaming support.

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Access External Agents via Handoff or Delegation

Once registered, external agents are available as tools within Agent Platform agents. You can combine local and external agents in the same multi-agent workflow. To use an external agent, add it to the Handoff or Delegate section of your agent. The platform handles communication through the A2A protocol. In ABL, add the external agent under the HANDOFF or DELEGATE section and set LOCATION to REMOTE: 
HANDOFF:
  - TO: RemoteAgentName           # must match ExternalAgentConfig.name in the DB
    WHEN: <condition>
    LOCATION: REMOTE              # marks this as an external call
    ENDPOINT: "https://remote.example.com/a2a"  # inline URL (optional if DB config exists)
    PROTOCOL: A2A                 # only 'a2a' supported today
    ASYNC: true                   # optional: suspend + push-notification callback mode
    TIMEOUT: 300                  # optional: seconds
    CONTEXT:
      pass: [field1, field2]      # session/context variables to forward
      summary: "Why we're handing off"
      history: full               # none | summary_only | full | last_n
    RETURN: true                  # true = parent thread waits for response

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Remote-Specific Properties

PropertyValuesDescription
LOCATIONREMOTEMarks the tool as a remote agent.
ENDPOINTURL stringThe A2A endpoint. Supports {{config.*}} and {{env.*}} interpolation. This property is optional. If provided, it overrides the endpoint URL configured during agent registration.
PROTOCOLA2A or RESTThe communication protocol used to invoke the remote agent.
ASYNCtrue / falseEnables asynchronous dispatch with push-notification barriers. When set to true, configure the CALLBACK_BASE_URL environment variable. This value must be a publicly accessible HTTPS URL where the remote agent can post execution results.
TIMEOUTInteger (seconds)Maximum time to wait for a response from the remote agent before the request times out.
CONTEXT—Copies named fields from the current session’s gathered or set data values into the request metadata sent to the external agent.
RETURNtrue / falseWhether the parent thread waits for the response.

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Operating Modes

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Sync Mode

This is the default mode. The agent waits for a response from the external agent. The default timeout is 30 seconds. If the request times out, the ON_FAILURE event is triggered. 
- TO: Risk_Analyzer
  WHEN: intent contains "risk"
  LOCATION: REMOTE
  ENDPOINT: "http://localhost:4002"
  PROTOCOL: A2A
  CONTEXT:
    pass: [contract_id, contract_type]
    summary: "User needs risk analysis"
  RETURN: true

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Streaming

Streaming is auto-detected when the remote agent card has streaming: true and the user is connected. No DSL changes are required; the runtime handles it automatically. 
- TO: Risk_Analyzer
  WHEN: intent contains "risk"
  LOCATION: REMOTE
  ENDPOINT: "http://localhost:4002"
  PROTOCOL: A2A
  RETURN: true

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Async

Async mode uses a suspend-and-callback mechanism. The current session suspends, and the remote agent pushes the result when done. Use this mode for long-running operations. Requirements for async remote calls:
  • The CALLBACK_BASE_URL environment variable must be set to a public HTTPS URL reachable by the remote agent.
  • The remote agent’s card must have push notification capabilities.
  • Default async timeout is 300 seconds. Override with the TIMEOUT value in ABL.
- TO: Async_Risk_Analyzer
  WHEN: intent contains "deep analysis"
  LOCATION: REMOTE
  ENDPOINT: "http://localhost:4002"
  PROTOCOL: A2A
  ASYNC: true        # critical — forces suspend + callback path
  TIMEOUT: 300       # max wait in seconds
  CONTEXT:
    pass: [contract_id]
    summary: "Background deep analysis"
  RETURN: true
  1. Case sensitivity: TO: <external-agent-name> must exactly match the name provided during registration. The value is case-sensitive.
  2. Config variable: When using a config variable for the URL, {{config.EXTERNAL_AGENT_URL}} resolves at compile time, not runtime. The config variable must exist in the project before you save and deploy the agent. This approach is recommended for multi-environment setups. 
    - TO: Hosted_External_Agent
  WHEN: true
  LOCATION: REMOTE
  ENDPOINT: "{{config.EXTERNAL_AGENT_URL}}"   # set this in project config vars
  PROTOCOL: A2A
  CONTEXT:
    history: full
  RETURN: true
  3. Async callback: Push-notification callbacks require a public HTTPS URL set in the CALLBACK_BASE_URL environment variable.
  4. Inline endpoint: An inline ENDPOINT in DSL overrides the endpoint provided during registration. Authentication details must still be configured during registration—credentials cannot be added to the DSL.
  5. Remote agent state: Remote agents are stateless by default and only see the current message. Use history: full in CONTEXT to forward the conversation. The history is stored in message.metadata.history in the A2A payload.
  6. Context tracking: A contextId is sent on every turn to the same remote agent, allowing the remote side to associate turns if it maintains state.