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Rack middleware for rate-limiting incoming HTTP requests.
tag: 0.2.0

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HTTP Request Rate Limiter for Rack Applications

This is Rack middleware that provides logic for rate-limiting incoming HTTP requests to Rack applications. You can use Rack::Throttle with any Ruby web framework based on Rack, including with Ruby on Rails 3.0 and with Sinatra.


  • Throttles a Rack application by enforcing a minimum interval (by default, 1 second) between subsequent HTTP requests from a particular client.
  • Compatible with any Rack application and any Rack-based framework.
  • Stores rate-limiting counters in any key/value store implementation that responds to #[]/#[]= (like Ruby's hashes) or to #get/#set (like memcached or Redis).
  • Compatible with the gdbm binding included in Ruby's standard library.
  • Compatible with the memcached, memcache-client, memcache and redis gems.
  • Compatible with Heroku's memcached add-on (currently available as a free beta service).


Adding throttling to a Rackup application

require 'rack/throttle'

use Rack::Throttle::Interval

run lambda { |env| [200, {'Content-Type' => 'text/plain'}, "Hello, world!\n"] }

Enforcing a 3-second interval between requests

use Rack::Throttle::Interval, :min => 3.0

Using GDBM to store rate-limiting counters

require 'gdbm'
use Rack::Throttle::Interval, :cache =>'tmp/throttle.db')

Using Memcached to store rate-limiting counters

require 'memcached'
use Rack::Throttle::Interval, :cache =>, :key_prefix => :throttle

Using Redis to store rate-limiting counters

require 'redis'
use Rack::Throttle::Interval, :cache =>, :key_prefix => :throttle

HTTP Client Identification

The rate-limiting counters stored and maintained by Rack::Throttle are keyed to unique HTTP clients.

By default, HTTP clients are uniquely identified by their IP address as returned by Rack::Request#ip. If you wish to instead use a more granular, application-specific identifier such as a session key or a user account name, you need only subclass Rack::Throttle::Interval and override the #client_identifier method.

HTTP Response Codes and Headers

403 Forbidden (Rate Limit Exceeded)

When a client exceeds their rate limit, Rack::Throttle by default returns a "403 Forbidden" response with an associated "Rate Limit Exceeded" message in the response body.

An HTTP 403 response means that the server understood the request, but is refusing to respond to it and an accompanying message will explain why. This indicates an error on the client's part in exceeding the rate limits outlined in the acceptable use policy for the site, service, or API.

503 Service Unavailable (Rate Limit Exceeded)

However, there is an unfortunately widespread practice of instead returning a "503 Service Unavailable" response when a client exceeds the set rate limits. This is actually technically incorrect because it indicates an error on the server's part, which is certainly not the case with rate limiting - it was the client that committed the oops, not the server.

An HTTP 503 response would be correct in situations where the server was genuinely overloaded and couldn't handle more requests, but for rate limiting an HTTP 403 response is more appropriate. Nonetheless, if you think otherwise, Rack::Throttle does allow you to override the returned HTTP status code by passing in a :code => 503 option when constructing a Rack::Throttle::Limiter instance.


  • {Rack::Throttle}
    • {Rack::Throttle::Interval}
    • {Rack::Throttle::Daily}
    • {Rack::Throttle::Hourly}



The recommended installation method is via RubyGems. To install the latest official release, do:

% [sudo] gem install rack-throttle


To get a local working copy of the development repository, do:

% git clone git://

Alternatively, you can download the latest development version as a tarball as follows:

% wget



Rack::Throttle is free and unencumbered public domain software. For more information, see or the accompanying UNLICENSE file.

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