The shape of the runtime context available at invocation time.
If your agent defines a contextSchema, pass the inferred type here to get full type-safety
for runtime.context.
Function that receives the current agent state and runtime, and
returns the system prompt for the next model call as a string.
A middleware instance that sets systemPrompt for the next model call.
import { z } from "zod";
import { dynamicSystemPrompt } from "langchain";
import { createAgent, SystemMessage } from "langchain";
const contextSchema = z.object({ region: z.string().optional() });
const middleware = dynamicSystemPrompt<z.infer<typeof contextSchema>>(
(_state, runtime) => `You are a helpful assistant. Region: ${runtime.context.region ?? "n/a"}`
);
const agent = createAgent({
model: "anthropic:claude-3-5-sonnet",
contextSchema,
middleware: [middleware],
});
await agent.invoke({ messages }, { context: { region: "EU" } });
Dynamic System Prompt Middleware
Allows setting the system prompt dynamically right before each model invocation. Useful when the prompt depends on the current agent state or per-invocation context.