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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

It is recommended to also run gem install thin, which Sinatra will pick up if available.


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

get '/' do
  .. show something ..

post '/' do
  .. create something ..

put '/' do
  .. replace something ..

patch '/' do
  .. modify something ..

delete '/' do
  .. annihilate something ..

options '/' do
  .. appease 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"]

Or with block parameters:

get '/download/*.*' do |path, ext|
  [path, ext] # => ["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('/') { }

Custom Route Matchers

As shown above, Sinatra ships with built-in support for using String patterns and regular expressions as route matches. However, it does not stop there. You can easily define your own matchers:

class AllButPattern
  Match =

  def initialize(except)
    @except   = except
    @captures =[])

  def match(str)
    @captures unless @except === str

def all_but(pattern)

get all_but("/index") do
  # ...

Note that the above example might be over-engineered, as it can also be expressed as:

get // do
  pass if request.path_info == "/index"
  # ...

Or, using negative look ahead:

get %r{^(?!/index$)} do
  # ...

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

Each template language is exposed as via its own rendering method. These methods simply return a string:

get '/' do
  erb :index

This renders views/index.erb.

Instead of a template name, you can also just pass in the template content directly:

get '/' do
  code = "<%= >"
  erb code

Templates take a second argument, the options hash:

get '/' do
  erb :index, :layout => :post

This will render views/index.erb embedded in the views/post.erb (default is views/layout.erb, if it exists).

Any options not understood by Sinatra will be passed on to the template engine:

get '/' do
  haml :index, :format => :html5

You can also set options per template language in general:

set :haml, :format => :html5

get '/' do
  haml :index

Options passed to the render method override options set via set.

Available Options:


List of locals passed to the document. Handy with partials. Example: erb "<%= foo %>", :locals => {:foo => "bar"}


String encoding to use if uncertain. Defaults to settings.default_encoding.


Views folder to load templates from. Defaults to settings.views.


Whether to use a layout (true or false), if it's a Symbol, specifies what template to use. Example: erb :index, :layout => !request.xhr?


Content-Type the template produces, default depends on template language.


Scope to render template under. Defaults to the application instance. If you change this, instance variables and helper methods will not be available.


Template engine to use for rendering the layout. Useful for languages that do not support layouts otherwise. Defaults to the engine used for the temple. Example: set :rdoc, :layout_engine => :erb

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

set :views, settings.root + '/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.

Available Template Languages

Some languages have multiple implementations. To specify what implementation to use (and to be thread-safe), you should simply require it first:

require 'rdiscount' # or require 'bluecloth'
get('/') { markdown :index }

Haml Templates



File Extensions



haml :index, :format => :html5

Erb Templates


erubis or erb (included in Ruby)

File Extensions

.erb, .rhtml or .erubis (Erubis only)


erb :index

Builder Templates



File Extensions



builder { |xml| xml.em "hi" }

It also takes a block for inline templates (see example).

Nokogiri Templates



File Extensions



builder { |xml| xml.em "hi" }

It also takes a block for inline templates (see example).

Sass Templates



File Extensions



sass :stylesheet, :style => :expanded

SCSS Templates



File Extensions



scss :stylesheet, :style => :expanded

Less Templates



File Extensions



less :stylesheet

Liquid Templates



File Extensions



liquid :index, :locals => { :key => 'value' }

Since you cannot call Ruby methods (except for yield) from a Liquid template, you almost always want to pass locals to it.

Markdown Templates


rdiscount, redcarpet, bluecloth, kramdown or maruku

File Extensions

.markdown, .mkd and .md


markdown :index, :layout_engine => :erb

It is not possible to call methods from markdown, nor to pass locals to it. You therefore will usually use it in combination with another rendering engine:

erb :overview, :locals => { :text => markdown(:introduction) }

Note that you may also call the markdown method from within other templates:

%h1 Hello From Haml!
%p= markdown(:greetings)

Since you cannot call Ruby from Markdown, you cannot use layouts written in Markdown. However, it is possible to use another rendering engine for the template than for the layout by passing the :layout_engine option.

Textile Templates



File Extensions



textile :index, :layout_engine => :erb

It is not possible to call methods from textile, nor to pass locals to it. You therefore will usually use it in combination with another rendering engine:

erb :overview, :locals => { :text => textile(:introduction) }

Note that you may also call the textile method from within other templates:

%h1 Hello From Haml!
%p= textile(:greetings)

Since you cannot call Ruby from Textile, you cannot use layouts written in Textile. However, it is possible to use another rendering engine for the template than for the layout by passing the :layout_engine option.

RDoc Templates



File Extensions



textile :README, :layout_engine => :erb

It is not possible to call methods from rdoc, nor to pass locals to it. You therefore will usually use it in combination with another rendering engine:

erb :overview, :locals => { :text => rdoc(:introduction) }

Note that you may also call the rdoc method from within other templates:

%h1 Hello From Haml!
%p= rdoc(:greetings)

Since you cannot call Ruby from RDoc, you cannot use layouts written in RDoc. However, it is possible to use another rendering engine for the template than for the layout by passing the :layout_engine option.

Radius Templates



File Extensions



radius :index, :locals => { :key => 'value' }

Since you cannot call Ruby methods directly from a Radius template, you almost always want to pass locals to it.

Markaby Templates



File Extensions



markaby { h1 "Welcome!" }

It also takes a block for inline templates (see example).

Slim Templates



File Extensions



slim :index

Creole Templates



File Extensions



creole :wiki, :layout_engine => :erb

It is not possible to call methods from creole, nor to pass locals to it. You therefore will usually use it in combination with another rendering engine:

erb :overview, :locals => { :text => creole(:introduction) }

Note that you may also call the creole method from within other templates:

%h1 Hello From Haml!
%p= creole(:greetings)

Since you cannot call Ruby from Creole, you cannot use layouts written in Creole. However, it is possible to use another rendering engine for the template than for the layout by passing the :layout_engine option.

CoffeeScript Templates


coffee-script and a way to execute javascript

File Extensions



coffee :index

Embedded Templates

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

Renders the embedded template string.

Accessing Variables in Templates

Templates are evaluated within the same context as route handlers. Instance variables set in route handlers are directly 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 => { :bar => 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 individually disable layouts by passing :layout => false or disable them by default via set :haml, :layout => false:

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

Associating File Extensions

To associate a file extension with a template engine, use Tilt.register. For instance, if you like to use the file extension tt for Textile templates, you can do the following:

Tilt.register :tt, Tilt[:textile]

Adding Your Own Template Engine

First, register your engine with Tilt, then create a rendering method:

Tilt.register :myat, MyAwesomeTemplateEngine

helpers do
  def myat(*args) render(:myat, *args) end

get '/' do
  myat :index

Renders ./views/index.myat. See to learn more about Tilt.


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 filters 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

Note: Unless you use the body method rather than just returning a String from the routes, the body will not yet be available in the after filter, since it is generated later on.

Filters optionally take a pattern, causing them to be evaluated only if the request path matches that pattern:

before '/protected/*' do

after '/create/:slug' do |slug|
  session[:last_slug] = slug

Like routes, filters also take conditions:

before :agent => /Songbird/ do
  # ...

after '/blog/*', :host_name => '' do
  # ...


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

Using Sessions

A session is used to keep state during requests. If activated, you have one session hash per user session:

enable :sessions

get '/' do
  "value = " << session[:value].inspect

get '/:value' do
  session[:value] = params[:value]

Note that enable :sessions actually stores all data in a cookie. This might not always be what you want (storing lots of data will increase your traffic, for instance). You can use any Rack session middleware: in order to do so, do not call enable :sessions, but instead pull in your middleware of choice how you would any other middleware:

use Rack::Session::Pool, :expire_after => 2592000

get '/' do
  "value = " << session[:value].inspect

get '/:value' do
  session[:value] = params[:value]

To improve security, the session data in the cookie is signed with a session secret. A random secret is generate for you by Sinatra. However, since this secret will change with every start of your application, you might want to set the secret yourself, so all your application instances share it:

set :session_secret, 'super secret'

If you want to configure it further, you may also store a hash with options in the sessions setting:

set :sessions, :domain => ''


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'

It is of course possible to combine a template with halt:

halt erb(:error)


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.

Triggering Another Route

Sometimes pass is not what you want, instead you would like to get the result of calling another route. Simply use call to achieve this:

get '/foo' do
  status, headers, body = call env.merge("PATH_INFO" => '/bar')
  [status, headers,]

get '/bar' do

Note that in the example above, you would ease testing and increase performance by simply moving "bar" into a helper used by both /foo and /bar.

If you want the request to be sent to the same application instance rather than a duplicate, use call! instead of call.

Check out the Rack specification if you want to learn more about call.

Setting Body, Status Code and Headers

It is possible and recommended to set the status code and response body with the return value of the route block. However, in some scenarios you might want to set the body at an arbitrary point in the execution flow. You can do so with the body helper method. If you do so, you can use that method from there on to access the body:

get '/foo' do
  body "bar"

after do
  puts body

It is also possible to pass a block to body, which will be executed by the Rack handler (this can be used to implement streaming, see “Return Values”).

Similar to the body, you can also set the status code and headers:

get '/foo' do
  status 418
  headers \
    "Allow"   => "BREW, POST, GET, PROPFIND, WHEN"
    "Refresh" => "Refresh: 20;"
  body "I'm a tea pot!"

Like body, headers and status with no arguments can be used to access their current values.


In the request scope, the logger helper exposes a Logger instance:

get '/' do "loading data"
  # ...

This logger will automatically take your Rack handler's logging settings into account. If logging is disabled, this method will return a dummy object, so you do not have to worry in your routes and filters about it.

Note that logging is only enabled for Sinatra::Application by default, so if you inherit from Sinatra::Base, you probably want to enable it yourself:

class MyApp < Sinatra::Base
  configure(:production, :development) do
    enable :logging

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:

configure do
  mime_type :foo, 'text/foo'

You can also use it with the content_type helper:

get '/' do
  content_type :foo
  "foo foo foo"

Generating URLs

For generating URLs you should use the url helper method, for instance, in Haml:

%a{:href => url('/foo')} foo

It takes reverse proxies and Rack routers into account, if present.

This method is also aliased to to (see below for an example).

Browser Redirect

You can trigger a browser redirect with the redirect helper method:

get '/foo' do
  redirect to('/bar')

Any additional parameters are handled like arguments passed to halt:

redirect to('/bar'), 303
redirect '', 'wrong place, buddy'

You can also easily redirect back to the page the user came from with redirect back:

get '/foo' do
  "<a href='/bar'>do something</a>"

get '/bar' do
  redirect back

To pass arguments with a redirect, either add them to the query:

redirect to('/bar?sum=42')

Or use a session:

enable :session

get '/foo' do
  session[:secret] = 'foo'
  redirect to('/bar')

get '/bar' do

Cache Control

Setting your headers correctly is the foundation for proper HTTP caching.

You can easily set the Cache-Control header with like this:

get '/' do
  cache_control :public
  "cache it!"

Pro tip: Set up caching in a before filter:

before do
  cache_control :public, :must_revalidate, :max_age => 60

If you are using the expires helper to set the corresponding header, Cache-Control will be set automatically for you:

before do
  expires 500, :public, :must_revalidate

To properly use caches, you should consider using etag and last_modified. It is recommended to call those helpers before doing heavy lifting, as they will immediately flush a response if the client already has the current version in its cache:

get '/article/:id' do
  @article = Article.find params[:id]
  last_modified @article.updated_at
  etag @article.sha1
  erb :article

It is also possible to use a weak ETag:

etag @article.sha1, :weak

These helpers will not do any caching for you, but rather feed the necessary information to your cache. If you are looking for a quick caching solutions, try rack-cache:

require "rack/cache"
require "sinatra"

use Rack::Cache

get '/' do
  cache_control :public, :max_age => 36000
  sleep 5

Sending Files

For sending files, you can use the send_file helper method:

get '/' do
  send_file 'foo.png'

It also takes a couple of options:

send_file 'foo.png', :type => :jpg

The options are:


file name, in response, defaults to the real file name.


value for Last-Modified header, defaults to the file's mtime.


content type to use, guessed from the file extension if missing.


used for Content-Disposition, possible values: nil (default), :attachment and :inline


Content-Length header, defaults to file size.

If supported by the Rack handler, other means than streaming from the Ruby process will be used. If you use this helper method, Sinatra will automatically handle range requests.

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
  t = %w[text/css text/html application/javascript]
  request.accept              # ['text/html', '*/*']
  request.accept? 'text/xml'  # true
  request.preferred_type(t)   # 'text/html'
  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.referrer            # the referrer 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 (would be true over ssl)
  request.forwarded?          # true (if running behind a reverse proxy)
  request.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']}!"


You can use the attachment helper to tell the browser the response should be stored on disk rather than displayed in the browser:

get '/' do
  "store it!"

You can also pass it a file name:

get '/' do
  attachment "info.txt"
  "store it!"

Looking Up Template Files

The find_template helper is used to find template files for rendering:

find_template settings.views, 'foo', Tilt[:haml] do |file|
  puts "could be #{file}"

This is not really useful. But it is useful that you can actually override this method to hook in your own lookup mechanism. For instance, if you want to be able to use more than one view directory:

set :views, ['views', 'templates']

helpers do
  def find_template(views, name, engine, &block)
    Array(views).each { |v| super(v, name, engine, &block) }

Another example would be using different directories for different engines:

set :views, :sass => 'views/sass', :haml => 'templates', :default => 'views'

helpers do
  def find_template(views, name, engine, &block)
    _, folder = views.detect { |k,v| engine == Tilt[k] }
    folder ||= views[:default]
    super(folder, name, engine, &block)

You can also easily wrap this up in an extension and share with others!

Note that find_template does not check if the file really exists but rather calls the given block for all possible paths. This is not a performance issue, since render will use break as soon as a file is found. Also, template locations (and content) will be cached if you are not running in development mode. You should keep that in mind if you write a really crazy method.


Run once, at startup, in any environment:

configure do
  # setting one option
  set :option, 'value'

  # setting multiple options
  set :a => 1, :b => 2

  # same as `set :option, true`
  enable :option

  # same as `set :option, false`
  disable :option

  # you can also have dynamic settings with blocks
  set(:css_dir) { File.join(views, 'css') }

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

You can access those options via settings:

configure do
  set :foo, 'bar'

get '/' do # => true  # => 'bar'

Available Settings


If disabled, Sinatra will allow relative redirects, however, Sinatra will no longer conform with RFC 2616 (HTTP 1.1), which only allows absolute redirects.

Enable if your app is running behind a reverse proxy that has not been set up properly. Note that the url helper will still produce absolute URLs, unless you pass in false as second parameter.

Disabled per default.


mime types the content_type helper will automatically add the charset info to.

You should add to it rather than overriding this option:

settings.add_charsets << "application/foobar"

main application file, used to detect project root, views and public folder and inline templates.


IP address to bind to (default: Only used for built-in server.


encoding to assume if unknown (defaults to "utf-8").


display errors in the log.


current environment, defaults to ENV['RACK_ENV'], or "development" if not available.


use the logger.


Places a lock around every request, only running processing on request per Ruby process concurrently.

Enabled if your app is not thread-safe. Disabled per default.


use _method magic to allow put/delete forms in browsers that don't support it.


Port to listen on. Only used for built-in server.


Whether or not to insert request.script_name into redirects if no absolute path is given. That way redirect '/foo' would behave like redirect to('/foo'). Disabled per default.


folder public files are served from


whether or not to reload templates between requests. Enabled in development mode.


project root folder.


raise exceptions (will stop application).


if enabled, Sinatra will handle starting the web server, do not enable if using rackup or other means.


is the built-in server running now? do not change this setting!


server or list of servers to use for built-in server. defaults to ['thin', 'mongrel', 'webrick'], order indicates priority.


enable cookie based sessions.


show a stack trace in the browser.


Whether Sinatra should handle serving static files. Disable when using a Server able to do this on its own. Disabling will boost performance. Enabled per default in classic style, disabled for modular apps.


views folder.

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...' + 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 an 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.

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 these components automatically based on configuration so you typically don't have to use them explicitly.

You can find useful middleware in rack, rack-contrib, with CodeRack or in the Rack wiki.


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

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 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.

Modular vs. Classic Style

Contrary to common belief, there is nothing wrong with classic style. If it suits your application, you do not have to switch to a modular application.

There are only two downsides compared with modular style:

  • You may only have one Sinatra application per Ruby process. If you plan to use more, switch to modular style.

  • Classic style pollutes Object with delegator methods. If you plan to ship your application in a library/gem, switch to modular style.

There is no reason you cannot mix modular and classic style.

If switching from one style to the other, you should be aware of slightly different default settings:

Setting             Classic                 Modular

app_file            file loading sinatra    file subclassing Sinatra::Base
run                 $0 == app_file          false
logging             true                    false
method_override     true                    false
inline_templates    true                    false
static              true                    false

Serving a Modular Application

There are two common options for starting a modular app, actively starting with run!:

# my_app.rb
require 'sinatra/base'

class MyApp < Sinatra::Base
  # ... app code here ...

  # start the server if ruby file executed directly
  run! if app_file == $0

Start with:

ruby my_app.rb

Or with a, which allows using any Rack handler:

require 'my_app'
run MyApp


rackup -p 4567

Using a Classic Style Application with a

Write your app file:

# app.rb
require 'sinatra'

get '/' do
  'Hello world!'

And a corresponding

require 'app'
run Sinatra::Application

When to use a

Good signs you probably want to use a

  • You want to deploy with a different Rack handler (Passenger, Unicorn, Heroku, …).

  • You want to use more than one subclass of Sinatra::Base.

  • You want to use Sinatra only for middleware, but not as endpoint.

There is no need to switch to a only because you switched to modular style, and you don't have to use modular style for running with a

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 :sessions

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

  post('/login') do
    if params[:name] == 'admin' && 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']}." }

Dynamic Application Creation

Sometimes you want to create new applications at runtime without having to assign them to a constant, you can do this with

require 'sinatra/base'
my_app = { get('/') { "hi" } }!

It takes the application to inherit from as optional argument:

require 'sinatra/base'

controller = do
  enable :logging
  helpers MyHelpers

map('/a') do
  run { get('/') { 'a' } }

map('/b') do
  run { get('/') { 'b' } }

This is especially useful for testing Sinatra extensions or using Sinatra in your own library.

This also makes using Sinatra as middleware extremely easy:

require 'sinatra/base'

use Sinatra do
  get('/') { ... }

run RailsProject::Application

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

  • The block passed to

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/options 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 following Ruby versions are officially supported:

Ruby 1.8.7

1.8.7 is fully supported, however, if nothing is keeping you from it, we recommend upgrading to 1.9.2 or switching to JRuby or Rubinius.

Ruby 1.9.2

1.9.2 is supported and recommended. Note that Radius and Markaby are currently not 1.9 compatible. Do not use 1.9.2p0, it is known to cause segmentation faults when running Sinatra.


Rubinius is officially supported (Rubinius >= 1.2.3), everything, including all template languages, works.


JRuby is officially supported (JRuby >= 1.6.1). No issues with third party template libraries are known, however, if you choose to use JRuby, please look into JRuby rack handlers, as the Thin web server is not fully supported on JRuby. JRuby's support for C extensions is still experimental, which only affects RDiscount and Redcarpet at the moment.

Ruby 1.8.6 is no longer supported.

We also keep an eye on upcoming Ruby versions.

The following Ruby implementations are not officially supported but still are known to run Sinatra:

  • Older versions of JRuby and Rubinius

  • MacRuby, Maglev, IronRuby

  • Ruby 1.9.0 and 1.9.1

Not being officially supported means if things only break there and not on a supported platform, we assume it's not our issue but theirs.

We also run our CI against ruby-head (the upcoming 1.9.3), but we can't guarantee anything, since it is constantly moving. Expect 1.9.3p0 to be supported.

Sinatra should work on any operating system supported by the chosen Ruby implementation.

The Bleeding Edge

If you would like to use Sinatra's latest bleeding code, feel free to run your application against the master branch, it should be rather stable.

We also push out prerelease gems from time to time, so you can do a

gem install sinatra --pre

To get some of the latest features.

With Bundler

If you want to run your application with the latest Sinatra, using Bundler is the recommended way.

First, install bundler, if you haven't:

gem install bundler

Then, in your project directory, create a Gemfile:

source :rubygems
gem 'sinatra', :git => "git://"

# other dependencies
gem 'haml'                    # for instance, if you use haml
gem 'activerecord', '~> 3.0'  # maybe you also need ActiveRecord 3.x

Note that you will have to list all your applications dependencies in there. Sinatra's direct dependencies (Rack and Tilt) will, however, be automatically fetched and added by Bundler.

Now you can run your app like this:

bundle exec ruby myapp.rb

Roll Your Own

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

To update the Sinatra sources in the future:

cd myapp/sinatra
git pull

Install Globally

You can build the gem on your own:

git clone git://
cd sinatra
rake sinatra.gemspec
rake install

If you install gems as root, the last step should be

sudo rake install


Sinatra follows Semantic Versioning, both SemVer and SemVerTag.

Further Reading