Customize prompt for Claude Code compatibility

custom-prompt.ts

import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";

const PI_TO_SDK_TOOL_NAME: Record<string, string> = {
	read: "Read",
	write: "Write",
	edit: "Edit",
	bash: "Bash",
	grep: "Grep",
	find: "Glob",
	glob: "Glob",
};

const toolDescriptions: Record<string, string> = {
	read: "Read file contents",
	bash: "Execute bash commands (ls, grep, find, etc.)",
	edit: "Make surgical edits to files (find exact text and replace)",
	write: "Create or overwrite files",
	grep: "Search file contents for patterns (respects .gitignore)",
	find: "Find files by glob pattern (respects .gitignore)",
	ls: "List directory contents",
};

function buildGuidelines(tools: string[]): string[] {
	const guidelines: string[] = [];

	const hasBash = tools.includes("bash");
	const hasEdit = tools.includes("edit");
	const hasWrite = tools.includes("write");
	const hasGrep = tools.includes("grep");
	const hasFind = tools.includes("find");
	const hasLs = tools.includes("ls");
	const hasRead = tools.includes("read");

	if (hasBash && !hasGrep && !hasFind && !hasLs) {
		guidelines.push("Use bash for file operations like ls, rg, find");
	} else if (hasBash && (hasGrep || hasFind || hasLs)) {
		guidelines.push("Prefer grep/find/ls tools over bash for file exploration (faster, respects .gitignore)");
	}

	if (hasRead && hasEdit) {
		guidelines.push("Use read to examine files before editing. You must use this tool instead of cat or sed.");
	}

	if (hasEdit) {
		guidelines.push("Use edit for precise changes (old text must match exactly)");
	}

	if (hasWrite) {
		guidelines.push("Use write only for new files or complete rewrites");
	}

	if (hasEdit || hasWrite) {
		guidelines.push(
			"When summarizing your actions, output plain text directly - do NOT use cat or bash to display what you did",
		);
	}

	guidelines.push("Be concise in your responses");
	guidelines.push("Show file paths clearly when working with files");

	return guidelines;
}

function buildCustomSystemPrompt(selectedTools: string[] = ["read", "bash", "edit", "write"]): string {
	const tools = selectedTools.filter((t) => t in toolDescriptions);
	const toolsList = tools.map((t) =>
		`- ${PI_TO_SDK_TOOL_NAME[t]}: ${toolDescriptions[t]}`).join("\n");
	const guidelines = buildGuidelines(tools);
	const guidelinesText = guidelines.map((g) => `- ${g}`).join("\n");

	// Customize this prompt to your needs
	return `You are Claude Code, Anthropic's official CLI for Claude. You are an expert coding assistant.

Available tools:
${toolsList}

In addition to the tools above, you may have access to other custom tools depending on the project.

Guidelines:
${guidelinesText}
`;
}

const extension = (pi: ExtensionAPI) => {
	pi.on("before_agent_start", async (_event) => {
		// Return systemPromptAppend instead of systemPrompt
		// This preserves Claude Code SDK's built-in CLAUDE.md handling
		return {
			systemPrompt: buildCustomSystemPrompt(),
		};
	});

	return { name: "custom-prompt" };
};

export default extension;