Azure Custom Decision Service provides two APIs that are called for each decision: the Ranking API to input the ranking of actions and the Reward API to output the reward. In addition, you provide an Action Set API to specify the actions to Azure Custom Decision Service. This article covers these three APIs. A typical scenario is used below to show when Custom Decision Service optimizes the ranking of articles.

Ranking API

The ranking API uses a standard JSONP-style communication pattern to optimize latency and bypass the same-origin policy. The latter prohibits JavaScript from fetching data from outside the page's origin.

Insert this snippet into the HTML head of your front page (where a personalized list of articles are displayed):

// define the "callback function" to render UI
<script> function callback(data) { … } </script>
// "data" provides the ranking of URLs, see example below.

// call to Ranking API
<script src="https://ds.microsoft.com/api/v2/<appId>/rank/<actionSetId>?<parameters>" async></script>
// action set id is the name of the corresponding RSS/Atom feed.

// same call with multiple action sets:
// <script src="https://ds.microsoft.com/api/v2/<appId>/rank/<A1>/<A2>/.../<An>?<parameters>" async></script>


The callback function must be defined before the call to the Ranking API.


To improve latency, the Ranking API is exposed via HTTP rather than HTTPS, as in http://ds.microsoft.com/api/v2/<appId>/rank/*. However, an HTTPS endpoint must be used if the front page is served through HTTPS.

When parameters are not used, the HTTP response from the Ranking API is a JSONP-formatted string:

   "ranking":[{"id":"url1"}, {"id":"url2"}, {"id":"url3"}],
   "eventId":"<opaque event string>",
   "appId":"<your app id>",

The browser then executes this string as a call to the callback() function.

The parameter to the callback function in the preceding example has the following schema:

  • ranking provides the ranking of URLs to be displayed.
  • eventId is used internally by Custom Decision Service to match this ranking with the corresponding clicks.
  • appId allows the callback function to distinguish between multiple applications of Custom Decision Service running on the same webpage.
  • actionSets lists each action set used in the Ranking API call, along with the UTC timestamp of the last successful refresh. Custom Decision Service periodically refreshes the action set feeds. For example, if some of the action sets are not current, the callback function might need to fall back to their default ranking.


The specified action sets are processed, and possibly pruned, to form the default ranking of articles. The default ranking then gets reordered and returned in the HTTP response. The default ranking is defined here:

  • Within each action set, the articles are pruned to the 15 most recent articles (if more than 15 are returned).
  • When multiple action sets are specified, they are merged in the same order as in the API call. The original ordering of the articles is preserved within each action set. Duplicates are removed in favor of the earlier copies.
  • The first n articles are kept from the merged list of articles, where n=20 by default.

Ranking API with parameters

The Ranking API allows these parameters:

  • details=1 and details=2 inserts additional details about each article listed in ranking.
  • limit=<n> specifies the maximal number of articles in the default ranking. n must be between 2 and 30 (or else it is truncated to 2 or 30, respectively).
  • dnt=1 disables user cookies.

Parameters can be combined in standard, query string syntax, for example details=2&dnt=1.


The default setting in Europe should be dnt=1 until the customer agrees to the cookie banner. It should also be the default setting for websites that target minors. For more information, see the terms of use.

The details=1 element inserts each article's guid, if it's served by the Action Set API. The HTTP response:

   "eventId":"<opaque event string>",
   "appId":"<your app id>",

The details=2 element adds more details that Custom Decision Service might extract from articles' SEO metatags featurization code:

  • title from <meta property="og:title" content="..." /> or <meta property="twitter:title" content="..." /> or <title>...</title>
  • description from <meta property="og:description" ... /> or <meta property="twitter:description" content="..." /> or <meta property="description" content="..." />
  • image from <meta property="og:image" content="..." />
  • ds_id from <meta name=”microsoft:ds_id” content="..." />

The HTTP response:

   "eventId":"<opaque event string>",
   "appId":"<your app id>",

The <details> element:

[{"guid":"123"}, {"description":"some text", "ds_id":"234", "image":"ImageUrl1", "title":"some text"}]

Reward API

Custom Decision Service uses clicks only on the top slot. Each click is interpreted as a reward of 1. The lack of a click is interpreted as a reward of 0. Clicks are matched with the corresponding rankings by using event IDs, which are generated by the Ranking API call. If needed, event IDs can be passed via session cookies.

To handle a click on the top slot, put this code on your front page:

    type: "POST",
    url: '//ds.microsoft.com/api/v2/<appId>/reward/' + data.eventId,
    contentType: "application/json" })

Here data is the argument to the callback() function, as described previously. Using data in the click handling code requires some care. An example is shown in this tutorial.

For testing only, the Reward API can be called via cURL:

curl -v https://ds.microsoft.com/api/v2/<appId>/reward/<eventId> -X POST -d 1 -H "Content-Type: application/json"

The expected effect is an HTTP response of 200 (OK). You can see the reward of 1 for this event in the log (if an Azure storage account key was supplied on the portal).

Action Set API (customer provided)

On a high level, the Action Set API returns a list of articles (actions). Each article is specified by its URL and (optionally) the article title and the publication date. You can specify several action sets on the portal. A different Action Set API should be used for each action set, as a distinct URL.

Each Action Set API can be implemented in two ways: as an RSS feed or as an Atom feed. Either one should conform to the standard and return a correct XML. For RSS, here's an example:

<rss version="2.0">
      <title><![CDATA[title (possibly with url) ]]></title>
      <guid>guid (could be a your internal database id)</guid>

Each top-level <item> element describes an action:

  • <link> is mandatory and is used as an action ID.
  • <date> is ignored if it's less than or equal to 15 items; otherwise, it's mandatory.
    • If there are more than 15 items, the 15 most recent ones are used.
    • It must be in the standard format for RSS or Atom, respectively:
      • RFC 822 for RSS: for example, "Fri, 28 Apr 2017 18:02:06 GMT"
      • RFC 3339 for Atom: for example, "2016-12-19T16:39:57-08:00"
  • <title> is optional and is used to generate features that describe the article.
  • <guid> is optional and passed through the system to the callback function (if the ?details parameter is specified in the Ranking API call).

Other elements inside an <item> are ignored.

The Atom feed version uses the same XML syntax and conventions.


If your system uses its own article IDs, they can be passed into the callback function by using <guid>.