A/B testing installation

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A/B testing enables you to test the impact of product changes and understand how they affect your users' behaviour. For example:

  • How changes to your onboarding flow affect your signup rate.
  • If different designs of your app's dashboard increase user engagement and retention.
  • The impact a free trial period versus money-back guarantee to determine which results in more customers.

A/B tests are also referred to as "experiments", and this is how we refer to them in the PostHog app.

To start using A/B tests, install PostHog with the library you want to run tests in (if you haven't already):

Option 1: Add the JavaScript snippet to your HTML Recommended

This is the simplest way to get PostHog up and running. It only takes a few minutes.

Copy the snippet below and replace <ph_project_api_key> and <ph_instance_address> with your project's values, then add it within the <head> tags at the base of your product - ideally just before the closing </head> tag. This ensures PostHog loads on any page users visit.

You can find the snippet pre-filled with this data in your project settings.

!function(t,e){var o,n,p,r;e.__SV||(window.posthog=e,e._i=[],e.init=function(i,s,a){function g(t,e){var o=e.split(".");2==o.length&&(t=t[o[0]],e=o[1]),t[e]=function(){t.push([e].concat(Array.prototype.slice.call(arguments,0)))}}(p=t.createElement("script")).type="text/javascript",p.async=!0,p.src=s.api_host+"/static/array.js",(r=t.getElementsByTagName("script")[0]).parentNode.insertBefore(p,r);var u=e;for(void 0!==a?u=e[a]=[]:a="posthog",u.people=u.people||[],u.toString=function(t){var e="posthog";return"posthog"!==a&&(e+="."+a),t||(e+=" (stub)"),e},u.people.toString=function(){return u.toString(1)+".people (stub)"},o="capture identify alias people.set people.set_once set_config register register_once unregister opt_out_capturing has_opted_out_capturing opt_in_capturing reset isFeatureEnabled onFeatureFlags getFeatureFlag getFeatureFlagPayload reloadFeatureFlags group updateEarlyAccessFeatureEnrollment getEarlyAccessFeatures getActiveMatchingSurveys getSurveys".split(" "),n=0;n<o.length;n++)g(u,o[n]);e._i.push([i,s,a])},e.__SV=1)}(document,window.posthog||[]);
posthog.init('<ph_project_api_key>', {api_host: '<ph_instance_address>'})

Once the snippet is added, PostHog automatically captures $pageview and other events like button clicks. You can then enable other products, such as session replays, within your project settings.

Option 2: Install via package manager

yarn add posthog-js

And then include it in your files:

import posthog from 'posthog-js'
posthog.init('<ph_project_api_key>', { api_host: '<ph_instance_address>' })

If you don't want to send test data while you're developing, you can do the following:

if (!window.location.host.includes('') && !window.location.host.includes('localhost')) {
posthog.init('<ph_project_api_key>', { api_host: '<ph_instance_address>' })

If you're using React or Next.js, checkout our React SDK or Next.js integration.


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Creating an experiment

To create a new experiment, go to the experiments tab in the PostHog app, and click on the "New experiment" button in the top right. This presents you with a form where you can complete the details of your new experiment: Here's a breakdown of each field in the form: Feature flag key Each experiment is backed by a feature flag . In your code, you use this feature flag key to check which experiment variant the user has been assigned to. The feature flag will be created for you automatically…

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