google--adk-python/contributing/samples/managed_agent/system_instruction

Managed Agent — System Instruction

For setup, authentication, backends, and background on ManagedAgent, see the ManagedAgent guide.

Overview

This sample runs a ManagedAgent whose behavior is shaped by its instruction field. instruction is forwarded to the Managed Agents API as the interaction's system instruction (the same role LlmAgent.instruction plays for a local model). Here it pins a persona and output format, so its effect is visible in every reply.

instruction accepts either a plain string (which may embed {state_var} placeholders resolved from session state) or an InstructionProvider callable. This sample uses an InstructionProvider: persona_instruction takes a ReadonlyContext, reads the reply language from state['response_language'] (defaulting to English), and returns the instruction string. Because a provider is invoked on every turn, the instruction is rebuilt each turn from the current state; unlike a string, it bypasses {placeholder} injection, so you build the final text yourself. A provider may also be async (return an awaitable str).

Sample Inputs

• What is the capital of France?

  The reply obeys the instruction: a single terse sentence ending with a relevant emoji, in the language from state['response_language'] (English by default).

• And Japan?

  A follow-up turn that reuses the recovered remote sandbox and previous interaction. The provider runs again on this turn, demonstrating that the system instruction is resolved and sent on chained turns too — and would pick up any change to response_language in session state.

Graph

graph LR
    User -->|message| ManagedAgent
    ManagedAgent -->|interactions.create + system_instruction| ManagedAgentsAPI
    ManagedAgentsAPI -->|streamed events| ManagedAgent
    ManagedAgent -->|reply shaped by the instruction| User

How To

• Set the instruction: pass instruction=... to ManagedAgent. A string is sent as-is (after {placeholder} resolution); an InstructionProvider callable is invoked per turn and bypasses placeholder injection.
• Use an InstructionProvider: define a callable that takes a ReadonlyContext and returns a str (or an awaitable str), then pass it as instruction. Read readonly_context.state to build the instruction dynamically — here state['response_language'] selects the reply language.
• Observe the effect: every reply follows the persona/format the instruction specifies, on the first turn and on chained follow-up turns.
• Drive it: a ManagedAgent is a BaseAgent, so a standard Runner runs it just like any other agent.