# Sinatra — Lightweight Ruby Web Framework

> A DSL for quickly creating web applications in Ruby with minimal effort and elegant syntax.

## Install

Save the content below to `.claude/skills/` or append to your `CLAUDE.md`:

# Sinatra — Lightweight Ruby Web Framework

## Quick Use
```bash
gem install sinatra
ruby -e "require 'sinatra'; get('/') { 'Hello, world!' }"
# Open http://localhost:4567
```

## Introduction
Sinatra is a minimal Ruby web framework that maps HTTP verbs directly to Ruby blocks. Created in 2007, it provides a simple DSL for routing and handling requests without the overhead of a full MVC stack, making it ideal for APIs, microservices, and small web applications.

## What Sinatra Does
- Maps HTTP methods (GET, POST, PUT, DELETE) to Ruby blocks with a one-liner DSL
- Renders views with ERB, Haml, Slim, and other template engines
- Handles URL parameters, query strings, and request bodies with simple accessors
- Supports before/after filters, helpers, and error handlers
- Serves as a Rack application, compatible with any Rack-based middleware or server

## Architecture Overview
Sinatra is built on Rack, the standard Ruby web server interface. Each route is a pair of an HTTP method and a URL pattern stored in a lookup table. When a request arrives, Sinatra matches it against registered routes in order, executes the matching block, and wraps the return value in a Rack response. The framework supports two modes: classic (top-level DSL) and modular (subclassing `Sinatra::Base`) for mounting multiple apps or using middleware. There is no ORM, migration system, or asset pipeline built in — you add only what you need.

## Self-Hosting & Configuration
- Install with `gem install sinatra` or add to a Gemfile with Bundler
- Run apps directly with `ruby app.rb` or use Rackup with a `config.ru` file
- Configure settings like port, environment, and logging via `set :option, value`
- Use Puma, Thin, or Falcon as the production Rack server
- Deploy anywhere Ruby runs: Heroku, Docker, systemd, or traditional hosting

## Key Features
- Routes defined in a single file with expressive HTTP verb methods
- Modular design lets you mount Sinatra apps as Rack middleware inside Rails or other frameworks
- Streaming and Server-Sent Events support for real-time responses
- Built-in development reloading via the `sinatra-reloader` extension
- Lightweight footprint under 2,000 lines of code

## Comparison with Similar Tools
- **Rails** — Full-stack MVC framework; Sinatra is minimal and requires you to choose your own components
- **Flask (Python)** — Similar micro-framework philosophy; Sinatra inspired Flask's route decorator pattern
- **Express (Node.js)** — Comparable minimalism in JavaScript; Sinatra predates Express and influenced its design
- **Hanami** — Modern Ruby framework with more structure; Sinatra trades structure for simplicity

## FAQ
**Q: When should I use Sinatra instead of Rails?**
A: Sinatra is a good fit for APIs, microservices, webhooks, and small apps where Rails' conventions would be overkill.

**Q: Can Sinatra scale to large applications?**
A: Yes, using the modular style with `Sinatra::Base`. However, for complex apps with many models and views, a full framework like Rails may be more productive.

**Q: Does Sinatra include an ORM?**
A: No. Pair it with ActiveRecord, Sequel, ROM, or any Ruby database library of your choice.

**Q: How does Sinatra handle testing?**
A: Sinatra provides `Rack::Test` integration for simulating HTTP requests in tests with RSpec, Minitest, or any Ruby test framework.

## Sources
- https://github.com/sinatra/sinatra
- https://sinatrarb.com

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Source: https://tokrepo.com/en/workflows/sinatra-lightweight-ruby-web-framework-2d8c7349
Author: AI Open Source