ADK Callbacks

[wify-vandana]

📚 Documentation Enhancement Suggestions for ADK

Hi team, while working extensively with the ADK agent system, I’ve encountered a few gaps in documentation that would greatly benefit from clarification. Here are my suggestions to improve the developer experience and make agent development more predictable and frontend-friendly:

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1. 🔁 Callback Behavior (Short-circuiting & Flow Control)

Please document what happens when a callback returns a Content object, especially in:

• after_tool_callback
• after_model_callback
• after_agent_callback

For example:

• Returning a Content from after_tool_callback prevents the model from being called again.
• after_agent_callback is skipped if a previous callback has already returned a final result.

📌 This kind of flow control is critical to understand but currently undocumented.

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2. 🧱 Structuring Final Agent Response for Frontend Chatbots

Please document best practices or built-in support for:

• Structuring final responses in a predictable JSON schema.
• Defining a response contract that works for custom chatbot UIs.
• Adding custom metadata to responses (e.g., type: info | success | error, quickReplies, etc.)

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3. 🔘 Adding Buttons / Quick Replies in Final Agent Response

There is no clear guidance on how to:

• Add buttons or interactive elements (like "quick replies") to the agent response.
• Define such buttons using FunctionCall, Part, or metadata.
• Support multi-modal outputs with both text and structured UI actions.

It would be helpful to show examples that include:

{
  "text": "Would you like to proceed?",
  "buttons": [
    { "label": "Yes", "action": "proceed_yes" },
    { "label": "No", "action": "proceed_no" }
  ]
}