anth-local-dev-loop

# Anthropic Local Dev Loop ## Overview Set up a fast local development cycle for Claude API projects with environment management, request logging, cost tracking, and hot-reload. ## Prerequisites - Completed `anth-install-auth` setup - Node.js 18+ or Python 3.8+ - `.env` file with `ANTHROPIC_API_KEY` ## Instructions ### Step 1: Project Structure ``` my-claude-app/ ├── .env # ANTHROPIC_API_KEY=sk-ant-... ├── .env.example # ANTHROPIC_API_KEY=your-key-here ├── .gitignore # Include .env ├── src/ │ ├── client.ts # Singleton client │ ├── prompts/ # System prompts as files │ └── tools/ # Tool definitions ├── tests/ │ └── mock-responses/ # Saved API responses for testing └── scripts/ └── dev.ts # Dev runner with logging ``` ### Step 2: Singleton Client with Request Logging ```typescript // src/client.ts import Anthropic from '@anthropic-ai/sdk'; let client: Anthropic | null = null; export function getClient(): Anthropic { if (!client) { client = new Anthropic({ apiKey: process.env.ANTHROPIC_API_KEY, maxRetries: 2, timeout: 30_000, }); } return client; } // Development logger — tracks cost per request export function logUsage(messageId: string, usage: { input_tokens: number; output_tokens: number }, model: string) { const pricing: Record<string, { input: number; output: number }> = { 'claude-sonnet-4-20250514': { input: 3.0, output: 15.0 }, 'cl...