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Sinatra is a DSL for quickly creating web-applications in Ruby with minimal effort:

# myapp.rb
require 'rubygems'
require 'sinatra'
get '/' do
  'Hello world!'

Install the gem and run with:

sudo gem install sinatra
ruby myapp.rb

View at: localhost:4567


In Sinatra, a route is an HTTP method paired with an URL matching pattern. Each route is associated with a block:

get '/' do
  .. show something ..

post '/' do
  .. create something ..

put '/' do
  .. update something ..

delete '/' do
  .. annihilate something ..

Routes are matched in the order they are defined. The first route that matches the request is invoked.

Route patterns may include named parameters, accessible via the params hash:

get '/hello/:name' do
  # matches "GET /foo" and "GET /bar"
  # params[:name] is 'foo' or 'bar'
  "Hello #{params[:name]}!"

You can also access named parameters via block parameters:

get '/hello/:name' do |n|
  "Hello #{n}!"

Route patterns may also include splat (or wildcard) parameters, accessible via the params[:splat] array.

get '/say/*/to/*' do
  # matches /say/hello/to/world
  params[:splat] # => ["hello", "world"]

get '/download/*.*' do
  # matches /download/path/to/file.xml
  params[:splat] # => ["path/to/file", "xml"]

Route matching with Regular Expressions:

get %r{/hello/([\w]+)} do
  "Hello, #{params[:captures].first}!"

Or with a block parameter:

get %r{/hello/([\w]+)} do |c|
  "Hello, #{c}!"

Routes may include a variety of matching conditions, such as the user agent:

get '/foo', :agent => /Songbird (\d\.\d)[\d\/]*?/ do
  "You're using Songbird version #{params[:agent][0]}"

get '/foo' do
  # Matches non-songbird browsers

Static Files

Static files are served from the ./public directory. You can specify a different location by setting the :public option:

set :public, File.dirname(__FILE__) + '/static'

Note that the public directory name is not included in the URL. A file ./public/css/style.css is made available as

Views / Templates

Templates are assumed to be located directly under the ./views directory. To use a different views directory:

set :views, File.dirname(__FILE__) + '/templates'

Haml Templates

The haml gem/library is required to render HAML templates:

get '/' do
  haml :index

Renders ./views/index.haml.

Erb Templates

get '/' do
  erb :index

Renders ./views/index.erb

Builder Templates

The builder gem/library is required to render builder templates:

get '/' do
  content_type 'application/xml', :charset => 'utf-8'
  builder :index

Renders ./views/index.builder.

Sass Templates

The sass gem/library is required to render Sass templates:

get '/stylesheet.css' do
  content_type 'text/css', :charset => 'utf-8'
  sass :stylesheet

Renders ./views/stylesheet.sass.

Inline Templates

get '/' do
  haml '%div.title Hello World'

Renders the inlined template string.

Accessing Variables in Templates

Templates are evaluated within the same context as route handlers. Instance variables set in route handlers are direcly accessible by templates:

get '/:id' do
  @foo = Foo.find(params[:id])
  haml '%h1='

Or, specify an explicit Hash of local variables:

get '/:id' do
  foo = Foo.find(params[:id])
  haml '%h1=', :locals => { :foo => foo }

This is typically used when rendering templates as partials from within other templates.

In-file Templates

Templates may be defined at the end of the source file:

require 'rubygems'
require 'sinatra'

get '/' do
  haml :index


@@ layout
  = yield

@@ index
%div.title Hello world!!!!!

NOTE: In-file templates defined in the source file that requires sinatra are automatically loaded. Call the use_in_file_templates! method explicitly if you have in-file templates in other source files.

Named Templates

Templates may also be defined using the top-level template method:

template :layout do
  "%html\n  =yield\n"

template :index do
  '%div.title Hello World!'

get '/' do
  haml :index

If a template named “layout” exists, it will be used each time a template is rendered. You can disable layouts by passing :layout => false.

get '/' do
  haml :index, :layout => !request.xhr?


Use the top-level helpers method to define helper methods for use in route handlers and templates:

helpers do
  def bar(name)

get '/:name' do


Before filters are evaluated before each request within the context of the request and can modify the request and response. Instance variables set in filters are accessible by routes and templates:

before do
  @note = 'Hi!'
  request.path_info = '/foo/bar/baz'

get '/foo/*' do
  @note #=> 'Hi!'
  params[:splat] #=> 'bar/baz'


To immediately stop a request during a before filter or route use:


You can also specify a body when halting …

halt 'this will be the body'

Or set the status and body …

halt 401, 'go away!'


A route can punt processing to the next matching route using pass:

get '/guess/:who' do
  pass unless params[:who] == 'Frank'
  "You got me!"

get '/guess/*' do
  "You missed!"

The route block is immediately exited and control continues with the next matching route. If no matching route is found, a 404 is returned.

Configuration and Reloading

Sinatra supports multiple environments and reloading. Reloading happens before each request when running under the :development environment. Wrap your configurations (e.g., database connections, constants, etc.) in configure blocks to protect them from reloading or to target specific environments.

Run once, at startup, in any environment:

configure do

Run only when the environment (RACK_ENV environment variable) is set to :production.

configure :production do

Run when the environment (RACK_ENV environment variable) is set to either :production or :test.

configure :production, :test do

Error handling

Error handlers run within the same context as routes and before filters, which means you get all the goodies it has to offer, like haml, erb, halt, etc.

Not Found

When a Sinatra::NotFound exception is raised, or the response's status code is 404, the not_found handler is invoked:

not_found do
  'This is nowhere to be found'


The error handler is invoked any time an exception is raised from a route block or before filter. The exception object can be obtained from the sinatra.error Rack variable:

error do
  'Sorry there was a nasty error - ' + env['sinatra.error'].name

Custom errors:

error MyCustomError do
  'So what happened was...' + request.env['sinatra.error'].message

Then, if this happens:

get '/' do
  raise MyCustomError, 'something bad'

You get this:

So what happened was... something bad

Sinatra installs special not_found and error handlers when running under the development environment.

Mime types

When using send_file or static files you may have mime types Sinatra doesn't understand. Use mime to register them by file extension:

mime :foo, 'text/foo'

Rack Middleware

Sinatra rides on Rack, a minimal standard interface for Ruby web frameworks. One of Rack's most interesting capabilities for application developers is support for “middleware” – components that sit between the server and your application monitoring and/or manipulating the HTTP request/response to provide various types of common functionality.

Sinatra makes building Rack middleware pipelines a cinch via a top-level use method:

require 'sinatra'
require 'my_custom_middleware'

use Rack::Lint
use MyCustomMiddleware

get '/hello' do
  'Hello World'

The semantics of use are identical to those defined for the Rack::Builder DSL (most frequently used from rackup files). For example, the use method accepts multiple/variable args as well as blocks:

use Rack::Auth::Basic do |username, password|
  username == 'admin' && password == 'secret'

Rack is distributed with a variety of standard middleware for logging, debugging, URL routing, authentication, and session handling. Sinatra uses many of of these components automatically based on configuration so you typically don't have to use them explicitly.


The Sinatra::Test mixin and Sinatra::TestHarness class include a variety of helper methods for testing your Sinatra app:

require 'my_sinatra_app'
require 'test/unit'
require 'sinatra/test'

class MyAppTest < Test::Unit::TestCase
  include Sinatra::Test

  def test_my_default
    get '/'
    assert_equal 'Hello World!', @response.body

  def test_with_params
    get '/meet', {:name => 'Frank'}
    assert_equal 'Hello Frank!', @response.body

  def test_with_rack_env
    get '/', {}, :agent => 'Songbird'
    assert_equal "You're using Songbird!", @response.body

See for more on Sinatra::Test and using it with other test frameworks such as RSpec, Bacon, and test/spec.

Command line

Sinatra applications can be run directly:

ruby myapp.rb [-h] [-x] [-e ENVIRONMENT] [-p PORT] [-s HANDLER]

Options are:

-h # help
-p # set the port (default is 4567)
-e # set the environment (default is development)
-s # specify rack server/handler (default is thin)
-x # turn on the mutex lock (default is off)

The Bleeding Edge

If you would like to use Sinatra's latest bleeding code, create a local clone and run your app with the sinatra/lib directory on the LOAD_PATH:

cd myapp
git clone git://
ruby -Isinatra/lib myapp.rb

Alternatively, you can add the sinatra/lib<tt> directory to the <tt>LOAD_PATH in your application:

$LOAD_PATH.unshift File.dirname(__FILE__) + '/sinatra/lib'
require 'rubygems'
require 'sinatra'

get '/about' do
  "I'm running version " + Sinatra::VERSION

To update the Sinatra sources in the future:

cd myproject/sinatra
git pull