Anth Local Dev Loop

What it does

When your agent uses it

• Setting up dev environment
• Configuring hot reload
• Establishing a fast iteration cycle with the Messages API
• With phrases like anthropic local dev

Example prompts

• “anthropic local dev”
• “claude dev setup”
• “anthropic development workflow”
• “/anth-local-dev-loop”

Requirements

• Python 3
• Node.js
• A credential in ANTHROPIC_API_KEY
• Compatibility (from SKILL.md): Designed for Claude Code
• Pre-approved tools (allowed-tools): Read, Write, Edit, Bash(npm:*), Bash(pip:*), Grep

Workflow steps

4 steps, taken from the step headings in SKILL.md.

1. 1Project Structure
2. 2Singleton Client with Request Logging
3. 3Mock Responses for Tests
4. 4Hot-Reload Dev Script

What it can do on your machine

Read from SKILL.md and the folder at commit cfae287. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Read
  • Write
  • Edit
  • Bash(npm:*)
  • Bash(pip:*)
  • Grep

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • tsx

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • platform.claude.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names these keys or tokens, usually read from environment variables:

  • ANTHROPIC_API_KEY

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Designed for Claude Code

  From compatibility in the SKILL.md frontmatter.

Context cost

Anth Local Dev Loop loads about 1.3k tokens when it runs. Until then it costs about 86 tokens; SKILL.md has 258 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~86

When it runs · the whole SKILL.md, loaded when a task matches

~1.3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• NoteMentions a .env fileSKILL.md:34

  - `.env` file with `ANTHROPIC_API_KEY`

• NoteMentions a .env fileSKILL.md:42

  ├── .env                  # ANTHROPIC_API_KEY=sk-ant-...

• NoteMentions a .env fileSKILL.md:44

  ├── .gitignore            # Include .env

• NoteMentions a .env fileSKILL.md:166

  | `.env` not loading | Missing dotenv setup | Use `dotenv` package or `tsx --env-file=.env` |

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from jeremylongshore/tons-of-skills-marketplace at commit cfae287, republished under its MIT licence (© jeremylongshore). 258 words, ~1,322 tokens.

name

anth-local-dev-loop

description

Configure a local development workflow for Anthropic Claude API projects. Use when setting up dev environment, configuring hot reload, or establishing a fast iteration cycle with the Messages API. Trigger with phrases like "anthropic local dev", "claude dev setup", "anthropic development workflow", "test claude locally".

allowed-tools

Read, Write, Edit, Bash(npm:*), Bash(pip:*), Grep

compatibility

Designed for Claude Code

version

1.7.0

license

MIT

author

Jeremy Longshore <jeremy@intentsolutions.io>

tags

saas, ai, anthropic

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

// 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 },
    'claude-haiku-4-20250514': { input: 0.80, output: 4.0 },
    'claude-opus-4-20250514': { input: 15.0, output: 75.0 },
  };
  const rates = pricing[model] || pricing['claude-sonnet-4-20250514'];
  const cost = (usage.input_tokens * rates.input + usage.output_tokens * rates.output) / 1_000_000;
  console.log(`[${messageId}] ${model} | ${usage.input_tokens}+${usage.output_tokens} tokens | $${cost.toFixed(4)}`);
}

// tests/mock-client.ts
import { type Message } from '@anthropic-ai/sdk/resources/messages';

export function mockMessage(text: string): Message {
  return {
    id: 'msg_test_123',
    type: 'message',
    role: 'assistant',
    model: 'claude-sonnet-4-20250514',
    content: [{ type: 'text', text }],
    stop_reason: 'end_turn',
    stop_sequence: null,
    usage: { input_tokens: 10, output_tokens: 20 },
  };
}

# package.json scripts
"scripts": {
  "dev": "tsx watch src/index.ts",
  "dev:debug": "ANTHROPIC_LOG=debug tsx watch src/index.ts",
  "test": "vitest",
  "test:live": "LIVE_API=1 vitest --run"
}

# .env.example (commit this)
ANTHROPIC_API_KEY=your-key-here
ANTHROPIC_MODEL=claude-sonnet-4-20250514
ANTHROPIC_MAX_TOKENS=1024
ANTHROPIC_LOG=warn     # debug | info | warn | error

# Enable SDK debug logging
export ANTHROPIC_LOG=debug  # Logs all requests/responses

import os

DEV_MODEL = "claude-haiku-4-20250514"      # $0.80/$4.00 per MTok
PROD_MODEL = "claude-sonnet-4-20250514"    # $3.00/$15.00 per MTok

model = DEV_MODEL if os.getenv("ENV") == "development" else PROD_MODEL

© jeremylongshore, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/.curated/anth-local-dev-loop of jeremylongshore/tons-of-skills-marketplace.

Open the folder on GitHubat commit cfae287