Go

This library uses an internal queue to make calls fast and non-blocking. It also batches requests and flushes asynchronously, making it perfect to use in any part of your web app or other server-side application that needs performance.

Installation

Terminal
go get github.com/posthog/posthog-go
Go
package main


import (
    "os"
    "github.com/posthog/posthog-go"
)


func main() {
    client, _ := posthog.NewWithConfig(
        os.Getenv("POSTHOG_API_KEY"),
        posthog.Config{
            PersonalApiKey: "your personal API key", // Optional, but much more performant.  If this token is not supplied, then fetching feature flag values will be slower.
            Endpoint:       "https://us.i.posthog.com",
        },
    )
    defer client.Close()
    // run commands
}

Identifying users

Identifying users is required. Backend events need a distinct_id that matches the ID your frontend uses when calling posthog.identify(). Without this, backend events are orphaned — they can't be linked to frontend event captures, session replays, LLM traces, or error tracking.

See our guide on identifying users for how to set this up.

Capturing events

You can send custom events using capture:

Go
client.Enqueue(posthog.Capture{
  DistinctId: "distinct_id_of_the_user",
  Event: "user_signed_up",
})

Tip: We recommend using a [object] [verb] format for your event names, where [object] is the entity that the behavior relates to, and [verb] is the behavior itself. For example, project created, user signed up, or invite sent.

Tip: You can define event schemas with typed properties and generate type-safe code using schema management.

Setting event properties

Optionally, you can include additional information with the event by including a properties object:

Go
client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id_of_the_user",
    Event:      "user_signed_up",
    Properties: posthog.NewProperties().
      Set("login_type", "email").
      Set("is_free_trial", true),
  })

Capturing pageviews

If you're aiming for a backend-only implementation of PostHog and won't be capturing events from your frontend, you can send pageviews from your backend like so:

Go
client.Enqueue(posthog.Capture{
  DistinctId: "distinct_id_of_the_user",
  Event:      "$pageview",
  Properties: posthog.NewProperties().
    Set("$current_url", "https://example.com"),
})

Person profiles and properties

For backward compatibility, the Go SDK captures identified events by default. These create person profiles. To set person properties in these profiles, include them when capturing an event:

Go
client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id",
    Event:      "event_name",
    Properties: map[string]interface{}{
        "$set": map[string]interface{}{
            "name": "Max Hedgehog",
        },
        "$set_once": map[string]interface{}{
            "initial_url": "/blog",
        },
    },
})

For more details on the difference between $set and $set_once, see our person properties docs.

To capture anonymous events without person profiles, set the event's $process_person_profile property to false:

Go
client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id",
    Event:      "event_name",
    Properties: map[string]interface{}{
        "$process_person_profile": false,
    },
})

Alias

Sometimes, you want to assign multiple distinct IDs to a single user. This is helpful when your primary distinct ID is inaccessible. For example, if a distinct ID used on the frontend is not available in your backend.

In this case, you can use alias to assign another distinct ID to the same user.

Go
client.Enqueue(posthog.Alias{
  DistinctId: "distinct_id",
  Alias: "alias_id",
})

We strongly recommend reading our docs on alias to best understand how to correctly use this method.

Feature flags

PostHog's feature flags enable you to safely deploy and roll back new features as well as target specific users and groups with them.

There are two steps to implement feature flags in Go:

Step 1: Evaluate flags once

Call client.EvaluateFlags() once for the user, then read values from the returned snapshot.

Boolean feature flags

Go
flags, err := client.EvaluateFlags(posthog.EvaluateFlagsPayload{
    DistinctId: "distinct_id_of_your_user",
})
if err != nil {
    // Handle error (e.g. capture error and fallback to default behavior)
}


if flags.IsEnabled("flag-key") {
    // Do something differently for this user
    // Optional: fetch the payload
    matchedFlagPayload := flags.GetFlagPayload("flag-key")
}

Multivariate feature flags

Go
flags, err := client.EvaluateFlags(posthog.EvaluateFlagsPayload{
    DistinctId: "distinct_id_of_your_user",
})
if err != nil {
    // Handle error (e.g. capture error and fallback to default behavior)
}


enabledVariant := flags.GetFlag("flag-key")


if enabledVariant == "variant-key" { // replace "variant-key" with the key of your variant
    // Do something differently for this user
    // Optional: fetch the payload
    matchedFlagPayload := flags.GetFlagPayload("flag-key")
}

flags.GetFlag() returns the variant string for multivariate flags, true for enabled boolean flags, false for disabled flags, and nil when the flag wasn't returned by the evaluation.

Note: client.IsFeatureEnabled(), client.GetFeatureFlag(), client.GetFeatureFlagPayload(), and Capture.SendFeatureFlags still work during the migration period, but they're deprecated. Prefer EvaluateFlags() for new code.

Step 2: Include feature flag information when capturing events

If you want use your feature flag to breakdown or filter events in your insights, you'll need to include feature flag information in those events. This ensures that the feature flag value is attributed correctly to the event.

Note: This step is only required for events captured using our server-side SDKs or API.

There are two methods you can use to include feature flag information in your events:

Method 1: Pass the evaluated flags snapshot to Capture

Pass the same flags object that you used for branching. This attaches the exact flag values from that evaluation and doesn't make another /flags request.

Go
flags, err := client.EvaluateFlags(posthog.EvaluateFlagsPayload{
    DistinctId: "distinct_id_of_your_user",
})
if err != nil {
    // Handle error
}


if flags.IsEnabled("flag-key") {
    // Do something differently for this user
}


client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id_of_your_user",
    Event:      "event_name",
    Flags:      flags,
})

By default, this attaches every flag in the snapshot using $feature/<flag-key> properties and $active_feature_flags.

To reduce event property bloat, pass a filtered snapshot:

Go
// Attach only flags accessed with IsEnabled() or GetFlag() before this call
client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id_of_your_user",
    Event:      "event_name",
    Flags:      flags.OnlyAccessed(),
})


// Attach only specific flags
client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id_of_your_user",
    Event:      "event_name",
    Flags:      flags.Only([]string{"checkout-flow", "new-dashboard"}),
})

OnlyAccessed() is order-dependent. If you call it before accessing any flags with IsEnabled() or GetFlag(), no feature flag properties are attached.

Method 2: Include the $feature/feature_flag_name property manually

In the event properties, include $feature/feature_flag_name: variant_key:

Go
client.Enqueue(posthog.Capture{
    DistinctId: "distinct_id_of_your_user",
    Event:      "event_name",
    Properties: posthog.NewProperties().
        Set("$feature/feature-flag-key", "variant-key"), // replace feature-flag-key with your flag key. Replace "variant-key" with the key of your variant
})

Evaluating only specific flags

By default, EvaluateFlags() evaluates every flag for the user. If you only need a few flags, pass FlagKeys to request only those flags:

Go
flags, err := client.EvaluateFlags(posthog.EvaluateFlagsPayload{
    DistinctId: "distinct_id_of_your_user",
    FlagKeys:   []string{"checkout-flow", "new-dashboard"},
})

Sending $feature_flag_called events

Capturing $feature_flag_called events enables PostHog to know when a flag was accessed by a user and provide analytics and insights on the flag. With EvaluateFlags(), the SDK sends this event when you call flags.IsEnabled() or flags.GetFlag() for a flag.

The SDK deduplicates these events per (distinct_id, flag, value) in a local cache. If you reinitialize the PostHog client, the cache resets and $feature_flag_called events may be sent again. PostHog handles duplicates, so duplicate $feature_flag_called events don't affect your analytics.

flags.GetFlagPayload() doesn't send $feature_flag_called events and doesn't count as an access for OnlyAccessed().

Advanced: Overriding server properties

Sometimes, you may want to evaluate feature flags using person properties, groups, or group properties that haven't been ingested yet, or were set incorrectly earlier.

You can provide properties to evaluate the flag with by using the person properties, groups, and group properties arguments. PostHog will then use these values to evaluate the flag, instead of any properties currently stored on your PostHog server.

For example:

Go
flags, err := client.EvaluateFlags(posthog.EvaluateFlagsPayload{
    DistinctId: "distinct_id_of_the_user",
    Groups: posthog.NewGroups().
        Set("your_group_type", "your_group_id").
        Set("another_group_type", "your_group_id"),
    PersonProperties: posthog.NewProperties().
        Set("property_name", "value"),
    GroupProperties: map[string]posthog.Properties{
        "your_group_type": posthog.NewProperties().
            Set("group_property_name", "value"),
        "another_group_type": posthog.NewProperties().
            Set("group_property_name", "value"),
    },
})
if err != nil {
    // Handle error
}


if flags.IsEnabled("flag-key") {
    // Do something differently for this user
}

Overriding GeoIP properties

By default, a user's GeoIP properties are set using the IP address they use to capture events on the frontend. You may want to override the these properties when evaluating feature flags. A common reason to do this is when you're not using PostHog on your frontend, so the user has no GeoIP properties.

You can override GeoIP properties by including them in the person_properties parameter when evaluating feature flags. This is useful when you're evaluating flags on your backend and want to use the client's location instead of your server's location.

The following GeoIP properties can be overridden:

  • $geoip_country_code
  • $geoip_country_name
  • $geoip_city_name
  • $geoip_city_confidence
  • $geoip_continent_code
  • $geoip_continent_name
  • $geoip_latitude
  • $geoip_longitude
  • $geoip_postal_code
  • $geoip_subdivision_1_code
  • $geoip_subdivision_1_name
  • $geoip_subdivision_2_code
  • $geoip_subdivision_2_name
  • $geoip_subdivision_3_code
  • $geoip_subdivision_3_name
  • $geoip_time_zone

Simply include any of these properties in the person_properties parameter alongside your other person properties when calling feature flags.

Request timeout

You can configure the FeatureFlagRequestTimeout parameter when initializing your PostHog client to set a flag request timeout. This helps prevent your code from being blocked if PostHog's servers are too slow to respond. By default, this is set to 3 seconds.

Go
client, _ := posthog.NewWithConfig(
    os.Getenv("<ph_project_token>"),
    posthog.Config{
        PersonalApiKey:            "your personal API key", // Optional, but much more performant. If this token is not supplied, then fetching feature flag values will be slower.
        Endpoint:                  "https://us.i.posthog.com",
        FeatureFlagRequestTimeout: 3, // Time in seconds. Defaults to 3.
    },
)

Local Evaluation

Evaluating feature flags requires making a request to PostHog for each flag. However, you can improve performance by evaluating flags locally. Instead of making a request for each flag, PostHog will periodically request and store feature flag definitions locally, enabling you to evaluate flags without making additional requests.

It is best practice to use local evaluation flags when possible, since this enables you to resolve flags faster and with fewer API calls.

For details on how to implement local evaluation, see our local evaluation guide.

Experiments (A/B tests)

Since experiments use feature flags, the code for running an experiment is very similar to the feature flags code:

Go
flags, err := client.EvaluateFlags(posthog.EvaluateFlagsPayload{
    DistinctId: "user_distinct_id",
})
if err != nil {
    // Handle error (e.g. capture error and fallback to default behavior)
}
variant := flags.GetFlag("experiment-feature-flag-key")


if variant == "variant-name" {
    // Do something
}

It's also possible to run experiments without using feature flags.

Error tracking

You can capture exceptions and errors using the Go SDK. There are two approaches:

Direct capture using NewDefaultException, which automatically generates a stack trace:

Go
exception := posthog.NewDefaultException(
    time.Now(),
    "user_distinct_id",
    "DatabaseError",      // type - rendered as title in the UI
    "connection refused",  // value - rendered as description in the UI
)
client.Enqueue(exception)

Automatic capture using the SlogCaptureHandler, which wraps Go's log/slog and sends log records at warning level and above as exceptions:

Go
baseHandler := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
    Level: slog.LevelInfo,
})
logger := slog.New(posthog.NewSlogCaptureHandler(baseHandler, client,
    posthog.WithDistinctIDFn(func(ctx context.Context, r slog.Record) string {
        return "user_distinct_id"
    }),
))


// Automatically captured as an exception in PostHog
logger.Warn("Something broke", "error", fmt.Errorf("connection refused"))

For the full setup guide, see the Go error tracking installation docs.

Group analytics

Group analytics allows you to associate an event with a group (e.g. teams, organizations, etc.). Read the Group Analytics guide for more information.

Note: This is a paid feature and is not available on the open-source or free cloud plan. Learn more on the pricing page.

  • Send an event associated with a group
Go
client.Enqueue(posthog.Capture{
    DistinctId: "user_distinct_id",
    Event:      "some_event",
    Groups: posthog.NewGroups().
        Set("company", "company_id_in_your_db"),
})
  • Update properties on a group
Go
client.Enqueue(posthog.GroupIdentify{
    Type: "company",
    Key:  "company_id_in_your_db",
    Properties: posthog.NewProperties().
        Set("name", "Awesome Inc.").
        Set("employees", 11),
})

The name is a special property which is used in the PostHog UI for the name of the group. If you don't specify a name property, the group ID will be used instead.

Thank you

This library is largely based on the analytics-go package.

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