ADK Plugin Architect

Philosophy & Architecture

Plugins are modular code blocks executed at various stages of an agent lifecycle. While callbacks are agent-specific, plugins are global and registered once on the Runner.

Key Capabilities

• •Precedence: Plugins run before agent-level callbacks.
• •Global Scope: Applies to all agents, tools, and LLMs managed by the Runner.
• •Flow Control: Intervene in the workflow (e.g., return cached responses) or amend context (e.g., add global instructions).

Callback Hooks

• •on_user_message_callback: First hook to run, inspect/modify raw user input.
• •before_run_callback / after_run_callback: Setup and teardown.
• •before_agent / after_agent: Intercept agent-level execution.
• •on_model_error / on_tool_error: Suppression of exceptions or graceful recovery.

Prebuilt Plugins

• •LoggingPlugin: Detailed traces.
• •ContextFilterPlugin: Context window compression.
• •GlobalInstructionPlugin: App-level prompts.
• •ReflectAndRetryPlugin: Tool failure recovery.

Success Criteria

• •Valid implementation of BasePlugin.
• •Correct registration in the Runner (plugins=[MyPlugin()]).
• •Successful interception of global execution flows.
• •Read references/plugins.md for hook definitions.