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Using the Event Conversion Measurement API

Using the Event Conversion Measurement API

Must-dos and tips to use the Event Conversion Measurement API.

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The Event Conversion Measurement API measures when an ad click leads to a conversion, without using cross-site identifiers. Here, you'll find must-dos and tips to use this API locally or as an experiment for your end users.

Demo

If you're considering using the API, see the demo and the corresponding code for a simple end-to-end implementation example.

Browser support

The Event Conversion Measurement API is supported:

  • As an origin trial, from Chrome 86 beta until Chrome 91 (April 2021). Origin trials enable the API for all visitors of a given origin. You need to register your origin for the origin trial in order to try the API with end users.
  • Or by turning on flags, in Chrome 86 and later. Flags enable the API on a single user's browser. Flags are useful when developing locally.

See details about the Chrome versions where the API is active on the Chrome feature entry.

Experiment with end users

Experiment with the API, with end users

To test the API with end users, you'll need to:

  1. Design your experiment.
  2. Set it up.
  3. Run it.

Design your experiment

Defining your goal will help you outline your plan for your experiment.

If your goal is to understand the API mechanics, run your experiment as follows:

  • Track conversions.
  • See how you can assign different values to conversion events.
  • Look at the conversion reports you're receiving.

If your goal is to see how well the API satisfies basic use cases, run your experiment as follows:

  • Track conversions.
  • Look at the aggregate count of conversions you're receiving.
  • Recover the corrected count of conversions. See how in Recover the corrected conversion count.
  • Optionally, if you want to try something more advanced: tweak the noise correction script. For example, try different groupings to see what sizes are necessary for the noise to be negligible.
  • Compare the corrected count of conversions with source-of-truth data (cookie-based conversion data).

Set up your experiment

Register for the origin trial

Registering for an origin trial is the first step to activate the API for end users. Upon registering for an origin trial, you have two choices to make: what type of tokens you need, and how the API usage should be controlled.

Token type:

  • If you're planning to use the API directly on your own origin(s), register your origin(s) for a regular origin trial.
  • If you're planning on using the API as a third-party—for example if you need to use the API in a script you wrote that is executed on origins you don't own—you may be eligible to register your origin for a third-party origin trial. This is convenient if you need to test at scale across different sites.

API usage control:

Origin trial features shouldn't exceed a small percentage of global page loads, because they're ephemeral. Because of this, sites that have registered for origin trials typically need to selectively enable API usage for small portions of their users. You can do this yourself, or let Chrome do this for you. In the dropdown How is (third-party) usage controlled?:

  • Select Standard limit to activate the API for all end users on origins where a token is present. Pick this if you don't need to A/B Test (with/without the experiment) or if you want to selectively enable API usage for small portions of your users yourself.
  • Select Exclude a subset of users to let Chrome selectively activate the API on a small subset of users on origins where a token is present. This consistently diverts a user into an experiment group across sites to avoid the usage limit. Pick this if you don't want to worry about implementing throttling for your API usage.
Gotchas!

If you pick Exclude a subset of users, the API won't be enabled for all users, even for origins that are registered for origin trials. This is the intended behaviour.

Add your origin trial tokens

Once your origin trial tokens are created, add them where relevant.

Adapt your code

If you've picked Exclude a subset of users, use client-side feature detection alongside the origin trial to check whether the API can be used.

Run your experiment

You're now ready to run your experiment.

(Optional) Recover the corrected conversion count

Even though the conversion data is noised, the reporting endpoint can recover the true count of reports that have a specific conversion value. See how in this noise corrector example script.

User privacy isn't impacted by this technique, because you can't determine whether a specific event's conversion data was noised. But this gives you the correct conversion count at an aggregated level.

Develop locally

A few tips when developing locally with the conversion measurement API.

Set up your browser for local development

  • Use Chrome version 86 or later. You can check what version of Chrome you're using by typing chrome://version in the URL bar.
  • To activate the feature locally (for example if you're developing on localhost), enable flags. Go to flags by typing chrome://flags in Chrome's URL bar. Turn on the two flags #enable-experimental-web-platform-features and #conversion-measurement-api.
  • Disable third-party cookie blocking. In the long term, dedicated browser settings will be available to allow/block the API. Until then, third-party cookie blocking is used as the signal that users don't want to share data about their conversions—and hence that this API should be disabled.
  • Don't use Incognito or Guest mode. The API is disabled on these profiles.
  • Some ad-blocking browser extensions may block some of the API's functionality (e.g. script names containing ad). Deactivate ad-blocking extensions on the pages where you need to test the API, or create a fresh user profile without extensions.

Debug

You can see the conversion reports the browser has scheduled to send at chrome://conversion-internals/ > Pending Reports. Reports are sent at scheduled times, but for debugging purposes you may want to get the reports immediately.

  • To receive all of the scheduled reports now, click Send All Reports in chrome://conversion-internals/ > Pending Reports.
  • To always receive reports immediately without having to click this button, enable the flag chrome://flags/#conversion-measurement-debug-mode.

Test your origin trial token(s)

If you've chosen Exclude a subset of users in the dropdown How is usage controlled? when you've registered your token(s), the API is only enabled for a subset of Chrome users. You may not be part of this group. To test your origin trial tokens, enforce that your browser behave as if it was in the selected Chrome group by enabling the flag #conversion-measurement-api.

Share your feedback

If you're experimenting with the API, your feedback is key in order to improve the API and support more use cases—please share it!

Further reading

With many thanks to Jxck and John Delaney for their feedback on this article.

Hero image by William Warby / @wawarby on Unsplash, edited.

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