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

# myapp.rb
require 'sinatra'

get '/' do
  'Hello world!'

Install the gem and run with:

gem install sinatra
ruby -rubygems 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 /hello/foo" and "GET /hello/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

Other available conditions are host_name and provides:

get '/', :host_name => /^admin\./ do
  "Admin Area, Access denied!"

get '/', :provides => 'html' do
  haml :index

get '/', :provides => ['rss', 'atom', 'xml'] do
  builder :feed

You can easily define your own conditions:

set(:probability) { |value| condition { rand <= value } }

get '/win_a_car', :probability => 0.1 do
  "You won!"

get '/win_a_car' do
  "Sorry, you lost."

Return values

The return value of a route block determines at least the response body passed on to the HTTP client, or at least the next middleware in the Rack stack. Most commonly this is a string, as in the above examples. But other values are also accepted.

You can return any object that would either be a valid Rack response, Rack body object or HTTP status code:

  • An Array with three elements: [status (Fixnum), headers (Hash), response body (responds to #each)]

  • An Array with two elements: [status (Fixnum), response body (responds to #each)]

  • An object that responds to #each and passes nothing but strings to the given block

  • A Fixnum representing the status code

That way we can for instance easily implement a streaming example:

class Stream
  def each
    100.times { |i| yield "#{i}\n" }

get('/') { }

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'

One important thing to remember is that you always have to reference templates with symbols, even if they're in a subdirectory (in this case use :'subdir/template'). You must use a symbol because otherwise rendering methods will render any strings passed to them directly.

Haml Templates

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

## You'll need to require haml in your app
require 'haml'

get '/' do
  haml :index

Renders ./views/index.haml.

Haml’s options can be set globally through Sinatra's configurations, see Options and Configurations, and overridden on an individual basis.

set :haml, :format => :html5 # default Haml format is :xhtml

get '/' do
  haml :index, :format => :html4 # overridden

Erb Templates

## You'll need to require erb in your app
require 'erb'

get '/' do
  erb :index

Renders ./views/index.erb


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

## You'll need to require erubis in your app
require 'erubis'

get '/' do
  erubis :index

Renders ./views/index.erubis

Builder Templates

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

## You'll need to require builder in your app
require 'builder'

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:

## You'll need to require haml or sass in your app
require 'sass'

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

Renders ./views/stylesheet.sass.

Sass’ options can be set globally through Sinatra's configurations, see Options and Configurations, and overridden on an individual basis.

set :sass, :style => :compact # default Sass style is :nested

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

Less Templates

The less gem/library is required to render Less templates:

## You'll need to require less in your app
require 'less'

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

Renders ./views/stylesheet.less.

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.

Inline Templates

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

require 'sinatra'

get '/' do
  haml :index


@@ layout
  = yield

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

NOTE: Inline templates defined in the source file that requires sinatra are automatically loaded. Call enable :inline_templates explicitly if you have inline 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 same context as the routes will be 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'

After filter are evaluated after each request within the same context and can also modify the request and response. Instance variables set in before filters and routes are accessible by after filters:

after do
  puts response.status


To immediately stop a request within a filter or route use:


You can also specify the status when halting:

halt 410

Or the body:

halt 'this will be the body'

Or both:

halt 401, 'go away!'

With headers:

halt 402, {'Content-Type' => 'text/plain'}, 'revenge'


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.

Accessing the Request Object

The incoming request object can be accessed from request level (filter, routes, error handlers) through the `request` method:

# app running on
get '/foo' do
  request.body              # request body sent by the client (see below)
  request.scheme            # "http"
  request.script_name       # "/example"
  request.path_info         # "/foo"
  request.port              # 80
  request.request_method    # "GET"
  request.query_string      # ""
  request.content_length    # length of request.body
  request.media_type        # media type of request.body              # ""
  request.get?              # true (similar methods for other verbs)
  request.form_data?        # false
  request["SOME_HEADER"]    # value of SOME_HEADER header
  request.referer           # the referer of the client or '/'
  request.user_agent        # user agent (used by :agent condition)
  request.cookies           # hash of browser cookies
  request.xhr?              # is this an ajax request?
  request.url               # ""
  request.path              # "/example/foo"
  request.ip                # client IP address           # false
  requuest.env              # raw env hash handed in by Rack

Some options, like script_name or path_info can also be written:

before { request.path_info = "/" }

get "/" do
  "all requests end up here"

The request.body is an IO or StringIO object:

post "/api" do
  request.body.rewind  # in case someone already read it
  data = JSON.parse
  "Hello #{data['name']}!"


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 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 a 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

Alternatively, you can install error handler for a status code:

error 403 do
  'Access forbidden'

get '/secret' do

Or a range:

error 400..510 do

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_type to register them by file extension:

mime_type :foo, 'text/foo'

You can also use it with the content_type helper:

content_type :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.


Sinatra tests can be written using any Rack-based testing library or framework. Rack::Test is recommended:

require 'my_sinatra_app'
require 'test/unit'
require 'rack/test'

class MyAppTest < Test::Unit::TestCase
  include Rack::Test::Methods

  def app

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

  def test_with_params
    get '/meet', :name => 'Frank'
    assert_equal 'Hello Frank!', last_response.body

  def test_with_rack_env
    get '/', {}, 'HTTP_USER_AGENT' => 'Songbird'
    assert_equal "You're using Songbird!", last_response.body

NOTE: The built-in Sinatra::Test module and Sinatra::TestHarness class are deprecated as of the 0.9.2 release.

Sinatra::Base - Middleware, Libraries, and Modular Apps

Defining your app at the top-level works well for micro-apps but has considerable drawbacks when building reusable components such as Rack middleware, Rails metal, simple libraries with a server component, or even Sinatra extensions. The top-level DSL pollutes the Object namespace and assumes a micro-app style configuration (e.g., a single application file, ./public and ./views directories, logging, exception detail page, etc.). That's where Sinatra::Base comes into play:

require 'sinatra/base'

class MyApp < Sinatra::Base
  set :sessions, true
  set :foo, 'bar'

  get '/' do
    'Hello world!'

The MyApp class is an independent Rack component that can act as Rack middleware, a Rack application, or Rails metal. You can use or run this class from a rackup file; or, control a server component shipped as a library:! :host => 'localhost', :port => 9090

The methods available to Sinatra::Base subclasses are exactly as those available via the top-level DSL. Most top-level apps can be converted to Sinatra::Base components with two modifications:

  • Your file should require sinatra/base instead of sinatra; otherwise, all of Sinatra's DSL methods are imported into the main namespace.

  • Put your app's routes, error handlers, filters, and options in a subclass of Sinatra::Base.

Sinatra::Base is a blank slate. Most options are disabled by default, including the built-in server. See Options and Configuration for details on available options and their behavior.

Using Sinatra as Middleware

Not only is Sinatra able to use other Rack middleware, any Sinatra application can in turn be added in front of any Rack endpoint as middleware itself. This endpoint could be another Sinatra application, or any other Rack-based application (Rails/Ramaze/Camping/…).

require 'sinatra/base'

class LoginScreen < Sinatra::Base
  enable :session

  get('/login') { haml :login }

  post('/login') do
    if params[:name] = 'admin' and params[:password] = 'admin'
      session['user_name'] = params[:name]
      redirect '/login'

class MyApp < Sinatra::Base
  # middleware will run before filters
  use LoginScreen

  before do
    unless session['user_name']
      halt "Access denied, please <a href='/login'>login</a>."

  get('/') { "Hello #{session['user_name']}." }

Scopes and Binding

The scope you are currently in determines what methods and variables are available.

Application/Class Scope

Every Sinatra application corresponds to a subclass of Sinatra::Base. If you are using the top level DSL (require 'sinatra'), then this class is Sinatra::Application, otherwise it is the subclass you created explicitly. At class level you have methods like `get` or `before`, but you cannot access the `request` object or the `session`, as there only is a single application class for all requests.

Options created via `set` are methods at class level:

class MyApp << Sinatra::Base
  # Hey, I'm in the application scope!
  set :foo, 42
  foo # => 42

  get '/foo' do
    # Hey, I'm no longer in the application scope!

You have the application scope binding inside:

  • Your application class body

  • Methods defined by extensions

  • The block passed to `helpers`

  • Procs/blocks used as value for `set`

You can reach the scope object (the class) like this:

  • Via the object passed to configure blocks (configure { |c| ... })

  • `settings` from within request scope

Request/Instance Scope

For every incoming request, a new instance of your application class is created and all handler blocks run in that scope. From within this scope you can access the `request` and `session` object or call rendering methods like `erb` or `haml`. You can access the application scope from within the request scope via the `settings` helper:

class MyApp << Sinatra::Base
  # Hey, I'm in the application scope!
  get '/define_route/:name' do
    # Request scope for '/define_route/:name'
    @value = 42

    settings.get("/#{params[:name]}") do
      # Request scope for "/#{params[:name]}"
      @value # => nil (not the same request)

    "Route defined!"

You have the request scope binding inside:

  • get/head/post/put/delete blocks

  • before/after filters

  • helper methods

  • templates/views

Delegation Scope

The delegation scope just forwards methods to the class scope. However, it does not behave 100% like the class scope, as you do not have the class' binding: Only methods explicitly marked for delegation are available and you do not share variables/state with the class scope (read: you have a different `self`). You can explicitly add method delegations by calling Sinatra::Delegator.delegate :method_name.

You have the delegate scope binding inside:

  • The top level binding, if you did require "sinatra"

  • An object extended with the `Sinatra::Delegator` mixin

Have a look at the code for yourself: here's the Sinatra::Delegator mixin being included into the main namespace.

Command line

Sinatra applications can be run directly:

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

Options are:

-h # help
-p # set the port (default is 4567)
-o # set the host (default is
-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 directory to the 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


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