Agent Config

You have a working agent and want the user to be able to tune how it behaves: tone, expertise level, response length, language, persona. By the end of this guide, your UI will own a typed config object that the agent reads on every run and rebuilds its system prompt from.

When to use this#

Reach for agent config whenever the agent's behaviour depends on user-controllable settings that don't fit naturally as chat input:

• Tone, voice, persona: "playful", "formal", "casual"
• Expertise level: "beginner", "intermediate", "expert"
• Response shape: short / medium / long, structured / prose, language
• Domain switches: which knowledge base to consult, which tool subset to enable

If the values are a channel the user occasionally tunes (a settings panel, a toolbar of selects), agent config is the right shape. If the values are content the agent should write back to (notes, a document, a plan), use Shared State instead.

How agent config flows from the UI into the agent's reasoning loop depends on your runtime architecture. Agents living behind a runtime read it from agent state on every run, while in-process agents receive the same object as forwarded properties on the provider — same UX, slightly different wiring on each side.

How it works#

Agent config is a typed object the frontend owns and keeps in sync with the agent. There are two pieces: the UI side, which owns the React state and pushes every change into agent state, and the backend node, which reads those fields out of state and turns them into a system prompt.

The UI side stays simple. Hold the typed config in React state, then mirror every change into the agent through agent.setState({...}):

function ConfigStateSync({ config }: { config: AgentConfig }) {
  const { agent } = useAgent({ agentId: "agent-config" });
  useEffect(() => {
    agent.setState({ ...config });
  }, [agent, config]);
  return null;
}

The backend half is also a single node. Read the config out of state at the top of every run and use it to build the system prompt for that turn:

async def my_agent_node(state: AgentState, config: RunnableConfig):
    cfg = state.get("config", {})
    tone = cfg.get("tone", "casual")
    expertise = cfg.get("expertise", "intermediate")
    response_length = cfg.get("response_length", "medium")
    system_prompt = build_system_prompt(tone, expertise, response_length)
    # ...

The agent reads the latest typed config at the start of every turn, rebuilds the system prompt, runs the turn. This is the same shape as the shared-state write-side pattern; agent config is just a specific use of that pattern with a UI-owned typed object on top.