co-mono/packages/coding-agent/examples/custom-tools

Custom Tools Examples

Example custom tools for pi-coding-agent.

Examples

Each example uses the subdirectory/index.ts structure required for tool discovery.

hello/

Minimal example showing the basic structure of a custom tool.

question/

Demonstrates pi.ui.select() for asking the user questions with options.

todo/

Full-featured example demonstrating:

• onSession for state reconstruction from session history
• Custom renderCall and renderResult
• Proper branching support via details storage
• State management without external files

subagent/

Delegate tasks to specialized subagents with isolated context windows. Includes:

• index.ts - The custom tool (single, parallel, and chain modes)
• agents.ts - Agent discovery helper
• agents/ - Sample agent definitions (scout, planner, reviewer, worker)
• commands/ - Workflow presets (/implement, /scout-and-plan, /implement-and-review)

See subagent/README.md for full documentation.

Usage

# Test directly (can point to any .ts file)
pi --tool examples/custom-tools/todo/index.ts

# Or copy entire folder to tools directory for persistent use
cp -r todo ~/.pi/agent/tools/

Then in pi:

> add a todo "test custom tools"
> list todos
> toggle todo #1
> clear todos

Writing Custom Tools

See docs/custom-tools.md for full documentation.

Key Points

Factory pattern:

import { Type } from "@sinclair/typebox";
import { StringEnum } from "@mariozechner/pi-ai";
import { Text } from "@mariozechner/pi-tui";
import type { CustomToolFactory } from "@mariozechner/pi-coding-agent";

const factory: CustomToolFactory = (pi) => ({
  name: "my_tool",
  label: "My Tool",
  description: "Tool description for LLM",
  parameters: Type.Object({
    action: StringEnum(["list", "add"] as const),
  }),
  
  // Called on session start/switch/branch/clear
  onSession(event) {
    // Reconstruct state from event.entries
  },
  
  async execute(toolCallId, params) {
    return {
      content: [{ type: "text", text: "Result" }],
      details: { /* for rendering and state reconstruction */ },
    };
  },
});

export default factory;

Custom rendering:

renderCall(args, theme) {
  return new Text(
    theme.fg("toolTitle", theme.bold("my_tool ")) + args.action,
    0, 0  // No padding - Box handles it
  );
},

renderResult(result, { expanded, isPartial }, theme) {
  if (isPartial) {
    return new Text(theme.fg("warning", "Working..."), 0, 0);
  }
  return new Text(theme.fg("success", "✓ Done"), 0, 0);
},

Use StringEnum for string parameters (required for Google API compatibility):

import { StringEnum } from "@mariozechner/pi-ai";

// Good
action: StringEnum(["list", "add"] as const)

// Bad - doesn't work with Google
action: Type.Union([Type.Literal("list"), Type.Literal("add")])