co-mono/packages/coding-agent/examples/sdk/03-custom-prompt.ts

/**
 * Custom System Prompt
 *
 * Shows how to replace or modify the default system prompt.
 */

import { createAgentSession, DefaultResourceLoader, SessionManager } from "@mariozechner/pi-coding-agent";

// Option 1: Replace prompt entirely
const loader1 = new DefaultResourceLoader({
	systemPromptOverride: () => `You are a helpful assistant that speaks like a pirate.
Always end responses with "Arrr!"`,
	// Needed to avoid DefaultResourceLoader appending APPEND_SYSTEM.md from ~/.pi/agent or <cwd>/.pi.
	appendSystemPromptOverride: () => [],
});
await loader1.reload();

const { session: session1 } = await createAgentSession({
	resourceLoader: loader1,
	sessionManager: SessionManager.inMemory(),
});

session1.subscribe((event) => {
	if (event.type === "message_update" && event.assistantMessageEvent.type === "text_delta") {
		process.stdout.write(event.assistantMessageEvent.delta);
	}
});

console.log("=== Replace prompt ===");
await session1.prompt("What is 2 + 2?");
console.log("\n");

// Option 2: Append instructions to the default prompt
const loader2 = new DefaultResourceLoader({
	appendSystemPromptOverride: (base) => [
		...base,
		"## Additional Instructions\n- Always be concise\n- Use bullet points when listing things",
	],
});
await loader2.reload();

const { session: session2 } = await createAgentSession({
	resourceLoader: loader2,
	sessionManager: SessionManager.inMemory(),
});

session2.subscribe((event) => {
	if (event.type === "message_update" && event.assistantMessageEvent.type === "text_delta") {
		process.stdout.write(event.assistantMessageEvent.delta);
	}
});

console.log("=== Modify prompt ===");
await session2.prompt("List 3 benefits of TypeScript.");
console.log();