GrowthBook native GO SDK example

README.md

Assuming you have GrowthBook running locally via docker-compose

Usage

go run main.go

Example response

2026/01/04 16:29:03 INFO Starting source="Growthbook polling datasource"
2026/01/04 16:29:03 INFO Loading features
2026/01/04 16:29:03 INFO First load finished source="Growthbook polling datasource"
2026/01/04 16:29:03 INFO Started source="Growthbook polling datasource"
2026/01/04 16:29:03 userContext: {
  "id": "02ae0723732ed10a0131ba519d3e1c98"
}
2026/01/04 16:29:03 Viewed Experiment
2026/01/04 16:29:03 Experiment: {
  "key": "myTrackingKey",
  "variations": [
    false,
    true
  ],
  "weights": [
    0.5,
    0.5
  ],
  "active": null,
  "coverage": 1,
  "ranges": null,
  "condition": {},
  "parentConditions": null,
  "namespace": null,
  "force": null,
  "hashAttribute": "id",
  "fallbackAttribute": "",
  "hashVersion": 2,
  "meta": [
    {
      "key": "0",
      "name": "Control",
      "passthrough": false
    },
    {
      "key": "1",
      "name": "Variation",
      "passthrough": false
    }
  ],
  "filters": null,
  "seed": "aab6cb2c-5bdb-4081-9bf3-849b69e11025",
  "name": "Experiemnt",
  "phase": "0",
  "disableStickyBucketing": false,
  "bucketVersion": 0,
  "minBucketVersion": 0
}
2026/01/04 16:29:03 Result: {
  "inExperiment": true,
  "variationId": 0,
  "value": false,
  "hashUsed": true,
  "hashAttribute": "id",
  "hashValue": "02ae0723732ed10a0131ba519d3e1c98",
  "featureId": "feature1",
  "key": "0",
  "bucket": 0.1083,
  "name": "Control",
  "passthrough": false,
  "stickyBucketUsed": false
}
2026/01/04 16:29:03 Extra: <nil>
2026/01/04 16:29:03 feature is off
2026/01/04 16:29:03 feature details: {
  "ruleId": "fr_1j14ku1omjwrctju",
  "value": false,
  "source": "experiment",
  "on": false,
  "off": true,
  "experiment": {
    "key": "myTrackingKey",
    "variations": [
      false,
      true
    ],
    "weights": [
      0.5,
      0.5
    ],
    "active": null,
    "coverage": 1,
    "ranges": null,
    "condition": {},
    "parentConditions": null,
    "namespace": null,
    "force": null,
    "hashAttribute": "id",
    "fallbackAttribute": "",
    "hashVersion": 2,
    "meta": [
      {
        "key": "0",
        "name": "Control",
        "passthrough": false
      },
      {
        "key": "1",
        "name": "Variation",
        "passthrough": false
      }
    ],
    "filters": null,
    "seed": "aab6cb2c-5bdb-4081-9bf3-849b69e11025",
    "name": "Experiemnt",
    "phase": "0",
    "disableStickyBucketing": false,
    "bucketVersion": 0,
    "minBucketVersion": 0
  },
  "experimentResult": {
    "inExperiment": true,
    "variationId": 0,
    "value": false,
    "hashUsed": true,
    "hashAttribute": "id",
    "hashValue": "02ae0723732ed10a0131ba519d3e1c98",
    "featureId": "feature1",
    "key": "0",
    "bucket": 0.1083,
    "name": "Control",
    "passthrough": false,
    "stickyBucketUsed": false
  }
}
2026/01/04 16:29:03 INFO Closing source="Growthbook polling datasource"

gb-api-response.json

{
  "status": 200,
  "features": {
    "feature1": {
      "defaultValue": false,
      "rules": [
        {
          "id": "fr_1j14ku1omjwr8e5i",
          "condition": {
            "id": "force1"
          },
          "force": true
        },
        {
          "id": "fr_1j14ku1omjwrctju",
          "coverage": 1,
          "hashAttribute": "id",
          "seed": "aab6cb2c-5bdb-4081-9bf3-849b69e11025",
          "hashVersion": 2,
          "variations": [
            false,
            true
          ],
          "weights": [
            0.5,
            0.5
          ],
          "key": "myTrackingKey",
          "meta": [
            {
              "key": "0",
              "name": "Control"
            },
            {
              "key": "1",
              "name": "Variation"
            }
          ],
          "phase": "0",
          "name": "Experiemnt"
        }
      ]
    }
  },
  "dateUpdated": "2026-01-02T12:47:29.283Z"
}

go.mod

module github.com/aurelijusb/fleature-flag-tests-gb-go

go 1.25.5

require github.com/growthbook/growthbook-golang v0.2.6

require github.com/tmaxmax/go-sse v0.10.0 // indirect

go.sum

github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/growthbook/growthbook-golang v0.2.6 h1:A6hclPLrtOYnleZ/yQUejCbUR5fQ4waDvwJb+oA8lEg=
github.com/growthbook/growthbook-golang v0.2.6/go.mod h1:mY8oBSateRALL7hMwr8UaPmsdm+10ffmgWIT1N5iQZE=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
github.com/tmaxmax/go-sse v0.10.0 h1:j9F93WB4Hxt8wUf6oGffMm4dutALvUPoDDxfuDQOSqA=
github.com/tmaxmax/go-sse v0.10.0/go.mod h1:u/2kZQR1tyngo1lKaNCj1mJmhXGZWS1Zs5yiSOD+Eg8=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

main.go

package main

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"log"
	"time"

	gb "github.com/growthbook/growthbook-golang"
)

func randomID() string {
	b := make([]byte, 16)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)
}

func main() {
	ctx := context.TODO()

	client, err := gb.NewClient(
		ctx,
		gb.WithApiHost("http://localhost:3100"),
		gb.WithClientKey("sdk-iyhSNglT6juJSHl"),
		gb.WithPollDataSource(30*time.Second),
		gb.WithExperimentCallback(func(
			ctx context.Context,
			experiment *gb.Experiment,
			result *gb.ExperimentResult,
			extra any,
		) {
			log.Println("Viewed Experiment")

			exp, _ := json.MarshalIndent(experiment, "", "  ")
			res, _ := json.MarshalIndent(result, "", "  ")

			log.Println("Experiment:", string(exp))
			log.Println("Result:", string(res))
			log.Println("Extra:", extra)
		}),
	)
	if err != nil {
		log.Fatal(err)
	}
	defer client.Close()

	if err := client.EnsureLoaded(context.TODO()); err != nil {
		log.Fatal("Client data load failed", "error", err)
	}

	// User context
	attrs := gb.Attributes{
		"id": randomID(), // replace with "force1" to test forced behavior
	}

	attrsJSON, _ := json.MarshalIndent(attrs, "", "  ")
	log.Println("userContext:", string(attrsJSON))

	scoped, err := client.WithAttributes(attrs)
	if err != nil {
		log.Fatal(err)
	}

	featureName := "feature1" // change to test missing feature

	details := scoped.EvalFeature(ctx, featureName)
	if details.On {
		log.Println("feature is on")
	} else {
		log.Println("feature is off")
	}
	detailsJSON, _ := json.MarshalIndent(details, "", "  ")
	log.Println("feature details:", string(detailsJSON))

	// give async callbacks time in very short-lived runs
	time.Sleep(100 * time.Millisecond)
}