Guide · Open source

How to use Sinatra: install, write routes and run a Ruby app

Updated 2026-10-29 · written with AI from the project's own documentation and checked against our catalogue data

Sinatra is a Ruby library, described in its README as a DSL for quickly creating web applications with minimal effort. This guide walks you through installing it, running your first app, and using routes, parameters and templates. By the end you will be able to build a small web app or API endpoint in a single Ruby file.

Sinatrasinatra/sinatra · ★ 12.5k · MIT Install options & downloads

Quick start

1Install Ruby. Make sure Ruby is installed, since Sinatra requires it.
2Install the gems. Run gem install sinatra rackup puma in your terminal.
3Create myapp.rb. Add require 'sinatra' and a get route that returns a string.
4Run the app. Start it with ruby myapp.rb and open http://localhost:4567.
5Add routes and parameters. Define more routes and read values from the params hash.
6Restart after changes. Restart the server after each code change, or use a reloader like rerun.

Install Sinatra and its prerequisites

Sinatra is written for Ruby, so you need Ruby installed first. Sinatra is installed as Ruby gems, using the gem command. The README installs three gems together: sinatra, rackup and puma.

Prerequisite: Ruby
Install with the gem command shown below

gem install sinatra rackup puma

Write and run your first Sinatra app

Create a file named myapp.rb. Sinatra uses the get method to define a route that matches a web address and an HTTP method. The block returns the response body, here the text 'Hello world!'.

Run the file with ruby, then open http://localhost:4567 in your browser. Changes to code do not take effect until you restart the server, so restart it after each edit or use a code reloader such as rerun or rack-unreloader.

# myapp.rb
require 'sinatra'

get '/' do
  'Hello world!'
end

# run with: ruby myapp.rb

Define routes and HTTP methods

A route is an HTTP method paired with a URL-matching pattern, and each route is associated with a block. Sinatra provides methods for get, post, put, patch, delete, options, link and unlink. Routes are matched in the order they are defined, and the first match is invoked.

Routes with a trailing slash are different from routes without one, so '/foo' does not match a request to '/foo/'.

get, post, put, patch, delete, options, link and unlink each map to an HTTP method
The first route that matches the request runs

get '/' do
  # show something
end

post '/' do
  # create something
end

Read URL parameters, splats and query strings

Named parameters in a route pattern are available through the params hash. You can also read them as block parameters. Splat (wildcard) parameters are available in params['splat'] as an array.

Query parameters such as ?title=foo are read the same way through params, and they are optional for the route.

Named parameters: params['name'] for a pattern like /hello/:name
Block parameters: |n| receives the named parameter
Splats: params['splat'] for patterns with *

get '/hello/:name' do
  "Hello #{params['name']}!"
end

get '/posts' do
  title = params['title']
  author = params['author']
end

Use templates and views

Sinatra supports many template languages, including Erb, Haml, Slim, Markdown and Liquid, among others listed in the README. A route can render a template by name, and templates can also be written inline or as named templates.

Variables set in a route are accessible in templates. The README also covers nested layouts using yield.

Erb and Haml are among the template languages listed in the README
Inline and named templates are both supported

Choose between classic and modular style

The classic style, shown in the examples above, is the shortest way to start. The modular style uses Sinatra::Base, which the README describes for middleware, libraries and modular apps. The README also explains how to serve either style with a config.ru file, using rackup.

For a single small file, the classic style is enough. Move to Sinatra::Base when the app grows or needs to be packaged as a library.

Classic style: the shortest start, as in the first example
Modular style: subclass Sinatra::Base
config.ru: described in the README for serving an app

What people use it for

Small web apps with a few pages
Quick prototypes to test an idea
Simple APIs with a handful of endpoints
Small internal tools for a team
Learning how web routes and requests work in Ruby

Frequently asked questions

Is Sinatra free to use?

Sinatra is open source and licensed under the MIT licence, as shown on its repository. You can use it in your projects under the terms of that licence.

What do I need to install Sinatra?

You need Ruby. Install the gems with gem install sinatra rackup puma, as the README shows.

How do I run a Sinatra app?

Save your code in a file such as myapp.rb and run it with ruby myapp.rb. Then open http://localhost:4567 in your browser.

Why are my code changes not showing up?

The README says changes take effect only after you restart the server. Restart it after each edit, or use a code reloader such as rerun or rack-unreloader.

Is Sinatra better than Rails?

Sinatra is a minimal DSL, so it suits small apps and APIs with a few endpoints. Rails is a full framework with built-in conventions for models, migrations and admin panels, so it suits larger applications.

Can I use Sinatra if my team does not use Ruby?

No. Sinatra is written for Ruby and requires it, so non-Ruby teams would need a different tool.

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Our verdict

Sinatra is a good fit for Ruby developers who want a small, readable web app, a quick prototype, or an API with a few endpoints. If you need a full framework with models, migrations and admin panels built in, Rails or Hanami are more suitable, and Roda or Rack are alternatives if you want a different level of minimalism.

Install options & downloads