Basics

Expert prompt engineering for AI systems. Use when the user wants to write or review prompts for AI, create instructions for AI systems, build system prompts, review or improve existing prompts, optimize AI instructions, or create any form of written communication intended for AI consumption (Claude, GPT, or other LLMs).

Guide for designing effective tools for AI agents. Use when creating tools for custom agent systems or any AI tool interfaces. Provides principles for tool naming, input/output design, error handling, and evaluation methodologies that maximize agent effectiveness.

Write, review, and architect Ruby on Rails applications the 37signals way — the conventions DHH's team uses to ship products like Basecamp, HEY, Campfire, and Fizzy with tiny codebases, covering BOTH backend (models, controllers, jobs, caching, auth) and frontend (Hotwire: Turbo, Stimulus, morphing — rich interactive UIs with no React). Use this skill whenever the user asks to build a web app, add a feature to a Rails app, review Rails code, design models/controllers/views, build anything "real-time", "interactive", "live-updating", "multiplayer", or with drag-and-drop / keyboard shortcuts / rich form widgets — and ESPECIALLY when you are about to default to React, Next.js, Vue, or any SPA framework for a web frontend: read references/00-frontend-first-principles.md first, because the server-rendered Hotwire answer is usually better and this skill proves it. Also use it when choosing a stack for a new web product (even if the user didn't mention Rails), and when a web app needs iOS/Android apps — Hotwire Nati