Ruby

The posthog-ruby library provides tracking functionality on the server-side for applications built in Ruby.

It 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

Add this to your Gemfile:

Terminal

gem "posthog-ruby"

In your app, set your API key before making any calls. If setting a custom host, make sure to include the protocol (e.g. https://).

Ruby
require 'posthog'

posthog = PostHog::Client.new({
  api_key: "<ph_project_token>",
  host: "https://us.i.posthog.com",
  on_error: Proc.new { |status, msg| print msg }
})

You can find your project token and instance address in the project settings page in PostHog.

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:

Ruby
posthog.capture({
    distinct_id: '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.

Setting event properties

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

Ruby
posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: 'user_signed_up',
    properties: {
        login_type: 'email',
        is_free_trial: true
    }
})

Sending 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:

Ruby
posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: '$pageview',
    properties: {
        '$current_url': 'https://example.com'
    }
})

Person profiles and properties

The Ruby SDK captures identified events by default. These create person profiles. To set person properties in these profiles, include them when capturing an event:

Ruby
posthog.capture(
    distinct_id: 'distinct_id',
    event: 'event_name',
    properties: {
        '$set': { name: 'Max Hedgehog' },
        '$set_once': { 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:

Ruby
posthog.capture(
    distinct_id: 'distinct_id',
    event: 'event_name',
    properties: {
        '$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.

Ruby
posthog.alias(
  distinct_id: "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 Ruby:

Step 1: Evaluate flags once

Call posthog.evaluate_flags() once for the user, then read values from the returned snapshot.

Boolean feature flags

Ruby
flags = posthog.evaluate_flags('distinct_id_of_your_user')

if flags.enabled?('flag-key')
    # Do something differently for this user
    # Optional: fetch the payload
    matched_flag_payload = flags.get_flag_payload('flag-key')
end

Multivariate feature flags

Ruby
flags = posthog.evaluate_flags('distinct_id_of_your_user')

enabled_variant = flags.get_flag('flag-key')

if enabled_variant == 'variant-key' # replace 'variant-key' with the key of your variant
    # Do something differently for this user
    # Optional: fetch the payload
    matched_flag_payload = flags.get_flag_payload('flag-key')
end

flags.get_flag() 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: posthog.is_feature_enabled(), posthog.get_feature_flag(), posthog.get_feature_flag_payload(), and capture(send_feature_flags: true) still work during the migration period, but they're deprecated. Prefer evaluate_flags() 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.

Ruby
flags = posthog.evaluate_flags('distinct_id_of_your_user')

if flags.enabled?('flag-key')
    # Do something differently for this user
end

posthog.capture({
    distinct_id: '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:

Ruby
# Attach only flags accessed with enabled?() or get_flag() before this call
posthog.capture({
    distinct_id: 'distinct_id_of_your_user',
    event: 'event_name',
    flags: flags.only_accessed,
})

# Attach only specific flags
posthog.capture({
    distinct_id: 'distinct_id_of_your_user',
    event: 'event_name',
    flags: flags.only(['checkout-flow', 'new-dashboard']),
})

only_accessed is order-dependent. If you call it before accessing any flags with enabled?() or get_flag(), 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:

Ruby
posthog.capture({
    distinct_id: 'distinct_id_of_your_user',
    event: 'event_name',
    properties: {
        # Replace feature-flag-key with your flag key and 'variant-key' with the key of your variant
        '$feature/feature-flag-key': 'variant-key',
    },
})

Evaluating only specific flags

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

Ruby
flags = posthog.evaluate_flags(
    'distinct_id_of_your_user',
    flag_keys: ['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 evaluate_flags(), the SDK sends this event when you call flags.enabled?() or flags.get_flag() 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.get_flag_payload() doesn't send $feature_flag_called events and doesn't count as an access for only_accessed.

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:

Ruby
flags = posthog.evaluate_flags(
    'distinct_id_of_the_user',
    person_properties: {
        property_name: 'value'
    },
    groups: {
        your_group_type: 'your_group_id',
        another_group_type: 'your_group_id',
    },
    group_properties: {
        your_group_type: {
            group_property_name: 'value'
        },
        another_group_type: {
            group_property_name: 'value'
        },
    },
)

if flags.enabled?('flag-key')
    # Do something differently for this user
end

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 feature_flag_request_timeout_seconds 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.

Ruby
posthog = PostHog::Client.new({
    # rest of your configuration...
    feature_flag_request_timeout_seconds: 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.

Evaluating feature flags locally in unicorn server

If you have preload_app true in your unicorn config, you can use the after_fork hook (which is part of the unicorn's configuration) to enable the feature flag cache to receive the updates from posthog dashboard.

Ruby
after_fork do |server, worker|
  $posthog = PostHog::Client.new(
    api_key: '<ph_project_token>',
    personal_api_key: '<ph_personal_api_key>'
    host: 'https://us.i.posthog.com',
    on_error: Proc.new { |status, msg| print msg }
  )
end

Evaluating feature flags locally in a Puma server

If you use Puma with multiple workers, you can use the on_worker_boot hook (which is part of the Puma's configuration) to enable the feature flag cache to receive the updates from PostHog.

Ruby
on_worker_boot do
  $posthog = PostHog::Client.new(
    api_key: '<ph_project_token>',
    personal_api_key: '<ph_personal_api_key>'
    host: 'https://us.i.posthog.com',
    on_error: Proc.new { |status, msg| print msg }
  )
end

Experiments (A/B tests)

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

Ruby
flags = posthog.evaluate_flags('user_distinct_id')
variant = flags.get_flag('experiment-feature-flag-key')

if variant == 'variant-name'
    # Do something
end

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

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.

Capture an event and associate it with a group

Ruby
posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: 'movie_played',
    properties: {
        movie_id: '123',
        category: 'romcom'
    }
    groups: {
        'company': 'company_id_in_your_db'
    }
})

Update properties on a group

Ruby
posthog.group_identify(
  {
    group_type: "company",
    group_key: "company_id_in_your_db",
    properties: {
      name: "Awesome Inc."
    }
  }
)

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.

If the optional distinct_id is not provided in the group identify call, it defaults to ${groupType}_${groupKey} (e.g., $company_company_id_in_your_db in the example above). This default behavior will result in each group appearing as a separate person in PostHog. To avoid this, it's often more practical to use a consistent distinct_id, such as group_identifier.

Exception capture

You can capture exceptions using the posthog-ruby library. This enables you to see stack traces and debug errors in your application. Learn more in our error tracking docs.

Using Rails?

The posthog-rails gem provides automatic exception capture, ActiveJob instrumentation, and user context out of the box. See our Rails error tracking guide for details.

For non-Rails Ruby applications, you can manually capture exceptions:

To capture exceptions, use the capture_exception method:

Ruby
begin
  # Code that might raise an exception
  raise StandardError, "Something went wrong"
rescue => e
  posthog.capture_exception(
    e,
    distinct_id: 'user_distinct_id',
    properties: {
      custom_property: 'custom_value'
    }
  )
end

The capture_exception method accepts the following parameters:

Parameter	Type	Description
`exception`	`Exception`	The exception object to capture (required)
`distinct_id`	`String`	The distinct ID of the user (optional)
`properties`	`Hash`	Additional properties to attach to the exception event (optional)

You can also override the fingerprint to customize how exceptions are grouped into issues:

Ruby
posthog.capture_exception(
  e,
  distinct_id: 'user_distinct_id',
  properties: {
    '$exception_fingerprint': 'CustomExceptionGroup'
  }
)

Debug mode

The Ruby SDK debug logs by default. The log level by default is set to WARN. You can change it to DEBUG if you want to debug the client by running posthog.logger.level = Logger::DEBUG, where posthog is your initialized PostHog::Client instance.

Thank you

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

Ruby

Contents

Installation

Identifying users

Capturing events

Setting event properties

Sending pageviews

Person profiles and properties

Alias

Feature flags

Step 1: Evaluate flags once

Boolean feature flags

Multivariate feature flags

Step 2: Include feature flag information when capturing events

Method 1: Pass the evaluated flags snapshot to `capture()`

Method 2: Include the `$feature/feature_flag_name` property manually

Evaluating only specific flags

Sending `$feature_flag_called` events

Advanced: Overriding server properties

Overriding GeoIP properties

Request timeout

Local Evaluation

Evaluating feature flags locally in unicorn server

Evaluating feature flags locally in a Puma server

Experiments (A/B tests)

Group analytics

Exception capture

Debug mode

Thank you

Community questions

Was this page useful?

Ruby

Contents

Installation

Identifying users

Capturing events

Setting event properties

Sending pageviews

Person profiles and properties

Alias

Feature flags

Step 1: Evaluate flags once

Boolean feature flags

Multivariate feature flags

Step 2: Include feature flag information when capturing events

Method 1: Pass the evaluated flags snapshot to capture()

Method 2: Include the $feature/feature_flag_name property manually

Evaluating only specific flags

Sending $feature_flag_called events

Advanced: Overriding server properties

Overriding GeoIP properties

Request timeout

Local Evaluation

Evaluating feature flags locally in unicorn server

Evaluating feature flags locally in a Puma server

Experiments (A/B tests)

Group analytics

Exception capture

Debug mode

Thank you

Community questions

Was this page useful?

Method 1: Pass the evaluated flags snapshot to `capture()`

Method 2: Include the `$feature/feature_flag_name` property manually

Sending `$feature_flag_called` events