Created: 2014-05-19 12:53
Updated: 2017-11-13 14:52


Build Status

This is a simple web service that uses Blitline to make it easy to render screenshots of Webmaker makes on-the-fly.


  • Node v0.10
  • A free Blitline account
  • An Amazon S3 bucket
  • Redis 2.6.17 or later

You can get a Blitline account either through their website, or via a free Heroku add-on.

The S3 bucket is used to upload screenshots into. You'll want to give Blitline permission to upload into it.

Quick Start

Note: The following instructions assume redis is installed at the default port on localhost. If this isn't the case, see below for configuring redis.

From the root directory, run:

npm install
npm test
export BLITLINE_APPLICATION_ID='your blitline application id'
export S3_BUCKET='your s3 bucket'
export DEBUG=
node app.js

At this point, you can visit http://localhost:3000/.


All POST endpoints take JSON-encoded bodies.


  • A viewport represents the dimensions of the display area that a webpage is rendered into. Examples include desktop and mobile.

  • A thumbnail represents a screenshot of a webpage on a particular viewport, usually scaled down to a specific resolution.

  • The default viewport is defined to be the first viewport listed in screenshot-config.json.

  • The default thumbnail for a viewport is defined to be the first thumbnail listed for a viewport in screenshot-config.json.

URL Parameters

  • :viewport is a viewport slug as defined in screenshot-config.json.

  • :thumbnail is a thumbnail slug for :viewport as defined in screenshot-config.json.

  • :key is either:

    • the hostname of the make followed by its path. Currently, makes can be hosted on a subdomain of makes.org or mofodev.net.
    • webmaker-desktop/:base64data, where :base64data is the base64-encoded URL of the make. This can include hashes and querystring arguments, so long as it is hosted at one of the following webmaker desktop domains:
      • webmaker-desktop-staging.herokuapp.com
      • beta.webmaker.org


GET /:viewport/:thumbnail/:key

Returns an HTTP redirect to a thumbnail of a Webmaker make for a particular viewport, generating it on-the-fly if needed.

So, for example, given a make at:


The large thumbnail of the desktop viewport can be found at:


Note that if the request's Accept header is set to application/json, this endpoint will not return an HTTP redirect; instead, it will return a 200 JSON response with a single property, screenshot, whose value is the absolute URL to the thumbnail image.

GET /:viewport/:key

Returns an HTTP redirect to the default thumbnail a Webmaker make on a particular viewport, generating it on-the-fly if needed.

GET /:key

Returns an HTTP redirect to the default thumbnail of a Webmaker make on the default viewport, generating it on-the-fly if needed.

POST /:viewport/:key

Regenerates all thumbnails of a make for a particular viewport.

Body parameters:

  • wait - If set to true, the screenshotting service will wait for several seconds before taking the screenshot. This is useful for pages that need extra time after the load event is fired to put themselves together. Defaults to false.

GET /healthcheck

Returns HTTP 200 if the server is OK, 500 if something is wrong.

Regardless, this endpoint always returns a JSON response with the following keys:

  • redis is a boolean indicating whether the server is currently connected to redis.

Discourse Support

The server hosts a client-side script that can automatically embed screenshots of Webmaker makes in a Discourse forum.

To enable it, in the Discourse admin panel, go to "Content", then "HTML head", and add a script tag to /js/discourse-onebox.js relative to the root of the screenshot server.

For instance, if your screenshot server is at https://example.org, then you'll want to add the following script tag:

<script src="https://example.org/js/discourse-onebox.js"></script>

For an example of this in action, see the Webmaker Discourse.

Optional Environment Variables

If your S3 bucket is hosted at a custom domain, you can optionally set S3_WEBSITE to its origin followed by a /, e.g. http://my-webmaker-screenshots.com/.

If your redis instance isn't at the default of port 6379 on localhost, you can define REDIS_URL to point at it. Use the form redis://:password@hostname:port.

REDISTOGO_URL is a synonym for REDIS_URL, to make deployment on Heroku easier.

If DEBUG is defined in the environment (even as an empty string), then some assets will be always be regenerated on-the-fly, which is useful for debugging.

If DEBUG is not defined then messina will be used for logging and you may want to set its GRAYLOG_* environment variables accordingly.

Running Tests

To run the test suite, run npm test.

Currently, the test suite assumes that redis is installed on localhost at the default port. At present, there is no way to override this.

There's also a manual test suite at http://localhost:3000/manual-test/.

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