Web experiments installation

Choose an installation method

Required

You can either add the JavaScript snippet directly to your HTML or install the JavaScript SDK via your package manager.

Add this snippet to your website within the <head> tag. This can also be used in services like Google Tag Manager:

HTML
<script>
    !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.replace(".i.posthog.com","-assets.i.posthog.com")+"/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="init capture register register_once register_for_session unregister opt_out_capturing has_opted_out_capturing opt_in_capturing reset isFeatureEnabled getFeatureFlag getFeatureFlagPayload reloadFeatureFlags group identify setPersonProperties setPersonPropertiesForFlags resetPersonPropertiesForFlags setGroupPropertiesForFlags resetGroupPropertiesForFlags resetGroups onFeatureFlags addFeatureFlagsHandler onSessionId getSurveys getActiveMatchingSurveys renderSurvey canRenderSurvey getNextSurveyStep".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_token>', {
        api_host: 'https://us.i.posthog.com',
        defaults: '2026-01-30'
    })
</script>

Install the PostHog JavaScript library using your package manager. Then, import and initialize the PostHog library with your project token and host:

npm install posthog-js
yarn add posthog-js
pnpm add posthog-js

JavaScript
import posthog from 'posthog-js'

posthog.init('<ph_project_token>', {
    api_host: 'https://us.i.posthog.com',
    defaults: '2026-01-30'
})

Implement your experiment

Required

Experiments run on top of our feature flags. You can define which version of your code runs based on the return value of the feature flag:

if (posthog.getFeatureFlag('your-experiment-feature-flag') === 'test') {
    // Do something differently for this user
} else {
    // It's a good idea to let control variant always be the default behaviour,
    // so if something goes wrong with flag evaluation, you don't break your app.
}

// Test that it works
posthog.featureFlags.overrideFeatureFlags({ flags: {'your-experiment-feature-flag': 'test'} })

3
Run your experiment
Required
Once you've implemented the feature flag in your code, you'll enable it for a target audience by creating a new experiment in the PostHog dashboard.

Next steps

Recommended

Now that you're running experiments, continue with the resources below to learn what else Experiments enables within the PostHog platform.

Resource	Description
Creating an experiment	How to create an experiment in PostHog
Adding experiment code	How to implement experiments for all platforms
Statistical significance	Understanding when results are meaningful
Experiment insights	How to analyze your experiment data
More tutorials	Other real-world examples and use cases

Web experiments installation

Choose an installation method

Implement your experiment

Run your experiment

Next steps

Community questions

Was this page useful?