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The GrowthBook PHP SDK requires PHP version 7.1 or greater.


GrowthBook is available on Composer:

composer require growthbook/growthbook

Quick Usage

// Create a GrowthBook instance
$growthbook = Growthbook\Growthbook::create()
// Targeting attributes
'id' => $userId,
'someCustomAttribute' => true

// Load feature flags from the GrowthBook API
// Make sure to use caching in production! (see 'Loading Features' below)
$growthbook->loadFeatures("sdk-abc123", "");

// Feature gating
if ($growthbook->isOn("my-feature")) {
echo "It's on!";
} else {
echo "It's off :(";

// Remote configuration with fallback
$color = $growthbook->getValue("button-color", "blue");
echo "<button style='color:${color}'>Click Me!</button>";

Some of the feature flags you evaluate might be running an A/B test behind the scenes which you'll want to track in your analytics system.

At the end of the request, you can loop through all experiments and track them however you want to:

$impressions = $growthbook->getViewedExperiments();
foreach($impressions as $impression) {
// Whatever you use for event tracking
"userId" => $userId,
"event" => "Experiment Viewed",
"properties" => [
"experimentId" => $impression->experiment->key,
"variationId" => $impression->result->key

Loading Features

There are 2 ways to load features into the SDK. You can use loadFeatures with a Client Key and API Host. Or, you can manually fetch and cache feature flags and pass them in with the withFeatures method.

loadFeatures method

The loadFeatures method can fetch features from the GrowthBook API for you.

By default, there is no caching enabled. You can enable it by passing any PSR16-compatible instance into the withCache method.

Caching is required for production usage

// Any psr-16 library will work
use Cache\Adapter\Apcu\ApcuCachePool;

$cache = new ApcuCachePool();

$growthbook = Growthbook\Growthbook::create()

// You can optionally pass in a TTL (default 60s)
$growthbook = Growthbook\Growthbook::create()
->withCache($cache, 120); // Cache for 120s instead

To load features, we require a PSR-17 (HttpClient) and PSR-18 (RequestFactoryInterface) compatible library like Guzzle to be installed.

We will auto-discover most HTTP libraries without any configuration required, but if you prefer to specify it explicitly, you can use the withHttpClient method. Note - you'll need to specify both an HttpClient and a RequestFactoryInterface implementation.

The loadFeatures method takes 3 arguments:

  • $clientKey (required) - Get this from your SDK Connection in GrowthBook.
  • $apiHost (optional) - Defaults to If self-hosting GrowthBook, set this to your API host.
  • $decryptionKey (optional) - Only required if you've enabled encryption for your SDK Connection.

withFeatures method

If you prefer to have full control over the fetching/caching behavior, you can use the withFeatures method instead to pass an associative array of features into the SDK.

// From the GrowthBook API, a custom cache layer, or somewhere else
$featuresJSON = '{"my-feature":{"defaultValue":true}}';

// Decode into an associative array
$features = json_decode($featuresJSON, true);

// Pass into the Growthbook instance
$growthbook = Growthbook\Growthbook::create()

The Growthbook Class

The Growthbook class has a number of properties. These can be set using a Fluent interface or can be passed into a constructor using an associative array. Every property also has a getter method if needed. Here's an example:

// Using the fluent interface
$growthbook = Growthbook\Growthbook::create()

// Using the constructor
$growthbook = new Growthbook\Growthbook([
'features' => $features,
'attributes' => $attributes

// Getter methods

Note: you can also use the fluent methods (e.g. withFeatures) at any point to update properties.


You can specify attributes about the current user and request. These are used for two things:

  1. Feature targeting (e.g. paid users get one value, free users get another)
  2. Assigning persistent variations in A/B tests (e.g. user id "123" always gets variation B)

Attributes can be any JSON data type - boolean, integer, float, string, or array.

$attributes = [
'id' => "123",
'loggedIn' => true,
'deviceId' => "abc123def456",
'age' => 21,
'tags' => ["tag1", "tag2"],
'account' => [
'age' => 90

If you want to update attributes later, please note that the withAttributes method completely overwrites the attributes object. You can use array_merge if you only want to update a subset of fields:

// Only update the url attribute
'url' => '/checkout'

Tracking Experiments

Any time an experiment is run to determine the value of a feature, you want to track that event in your analytics system.

You can either do this via a callback function:

$trackingCallback = function (
Growthbook\InlineExperiment $experiment,
Growthbook\ExperimentResult $result
) {
// example
"userId" => $userId,
"event" => "Experiment Viewed",
"properties" => [
"experimentId" => $experiment->key,
"variationId" => $result->key

// Fluent interface
$growthbook = Growthbook\Growthbook::create()

// Using the constructor
$growthbook = new Growthbook([
'trackingCallback' => $trackingCallback

// Getter method
$trackingCallback = $growthbook->getTrackingCallback();

Or track all events at the end of the request by looping through an array:

$impressions = $growthbook->getViewedExperiments();
foreach($impressions as $impression) {
// example
"userId" => $userId,
"event" => "Experiment Viewed",
"properties" => [
"experimentId" => $impression->experiment->key,
"variationId" => $impression->result->key

Or, you can pass the impressions onto your front-end and fire analytics events from there. To do this, simply add a block to your template (shown here in plain PHP, but similar idea for Twig, Blade, etc.).

<?php foreach($growthbook->getViewedExperiments() as $impression): ?>
// tracking code goes here
<?php endforeach; ?>

Below are examples for a few popular front-end tracking libraries:

Google Analytics

ga('send', 'event', 'experiment',
"<?= $impression->experiment->key ?>",
"<?= $impression->result->variationId ?>",
// Custom dimension for easier analysis
'dimension1': "<?=


analytics.track("Experiment Viewed", <?=json_encode([
"experimentId" => $impression->experiment->key,
"variationId" => $impression->result->key


mixpanel.track("Experiment Viewed", <?=json_encode([
'Experiment name' => $impression->experiment->key,
'Variant name' => $impression->result->key


GrowthBook can output log messages to help you debug your feature flags and experiments.

We support any PSR-3 comaptible logger. We implement a fluent interface (withLogger) as well as the standard LoggerAware interface (setLogger).

// Fluent interface

// Setter

Using Features

There are 3 main methods for interacting with features.

  • $growthbook->isOn("feature-key") returns true if the feature is on
  • $growthbook->isOff("feature-key") returns false if the feature is on
  • $growthbook->getValue("feature-key", "default") returns the value of the feature with a fallback

In addition, you can use $growthbook->getFeature("feature-key") to get back a FeatureResult object with the following properties:

  • value - The JSON-decoded value of the feature (or null if not defined)
  • on and off - The JSON-decoded value cast to booleans
  • source - Why the value was assigned to the user. One of unknownFeature, defaultValue, force, or experiment
  • experiment - Information about the experiment (if any) which was used to assign the value to the user
  • experimentResult - The result of the experiment (if any) which was used to assign the value to the user

Inline Experiments

Instead of declaring all features up-front and referencing them by ids in your code, you can also just run an experiment directly. This is done with the $growthbook->runInlineExperiment method:

$exp = Growthbook\InlineExperiment::create(
["red", "blue", "green"]

// Either "red", "blue", or "green"
echo $growthbook->runInlineExperiment($exp)->value;

As you can see, there are 2 required parameters for experiments, a string key, and an array of variations. Variations can be any data type, not just strings.

There are a number of additional settings to control the experiment behavior. The methods are all chainable. Here's an example that shows all of the possible settings:

$exp = Growthbook\InlineExperiment::create("my-experiment", ["red","blue"])
// Run a 40/60 experiment instead of the default even split (50/50)
->withWeights([0.4, 0.6])
// Only include 20% of users in the experiment
// Targeting conditions using a MongoDB-like syntax
'country' => 'US',
'browser' => [
'$in' => ['chrome', 'firefox']
// Use an alternate attribute for assigning variations (default is 'id')
// Namespaces are used to run mutually exclusive experiments
// Another experiment in the "pricing" namespace with a non-overlapping range
// will be mutually exclusive (e.g. [0.5, 1])
->withNamespace("pricing", 0, 0.5);

Inline Experiment Return Value

A call to runInlineExperiment returns an ExperimentResult object with a few useful properties:

$result = $growthbook->runInlineExperiment($exp);

// If user is part of the experiment
echo($result->inExperiment); // true or false

// The index of the assigned variation
echo($result->variationId); // e.g. 0 or 1

// The key used to identify this variation when tracking the event
echo($result->key); // e.g. "control"

// The value of the assigned variation
echo($result->value); // e.g. "A" or "B"

// If the variations was randomly assigned based on a hash
echo($result->hashUsed); // true or false

// The user attribute that was hashed
echo($result->hashAttribute); // "id"

// The value of that attribute
echo($result->hashValue); // e.g. "123"

The inExperiment flag will be false if the user was excluded from being part of the experiment for any reason (e.g. failed targeting conditions).

The hashUsed flag will only be true if the user was randomly assigned a variation. If the user was forced into a specific variation instead, this flag will be false.