How to create flag dependencies on PostHog

intermediate 8 min read Updated 2026-03-18

Quick Answer

Flag dependencies in PostHog allow you to control when feature flags are evaluated based on the state of other flags. You can create dependencies by accessing the flag settings and configuring prerequisite conditions that must be met before the dependent flag becomes active.

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Prerequisites

PostHog account with feature flags enabled
At least two existing feature flags in your project
Admin or write permissions for feature flags
Basic understanding of feature flag logic

Step-by-Step Instructions

Navigate to Feature Flags

Log into your PostHog dashboard and click on Feature Flags in the left sidebar. This will display all your existing feature flags in the project.

Make sure you have at least two feature flags created before setting up dependencies.

Select the Dependent Flag

Click on the feature flag that you want to make dependent on another flag. This will open the flag configuration page where you can modify its settings and behavior.

Choose the flag that should only activate when certain conditions are met by other flags.

Access Advanced Settings

Scroll down to the Advanced settings section or look for the Dependencies tab within the flag configuration. Click on Add dependency or Configure prerequisites.

Select Prerequisite Flag

In the dependency configuration, click the dropdown menu to select which flag this current flag should depend on. Choose from your existing feature flags that will serve as prerequisites.

You can add multiple prerequisite flags if needed for complex dependency chains.

Configure Dependency Conditions

Set the condition for the dependency by selecting:

Flag is enabled - prerequisite flag must be on
Flag is disabled - prerequisite flag must be off
Flag matches variant - prerequisite flag must return a specific variant value

Use variant matching for more granular control over flag dependencies.

Set Fallback Behavior

Configure what happens when the dependency condition is not met:

Return false - dependent flag will be disabled
Return specific variant - dependent flag returns a predetermined value
Skip evaluation - dependent flag won't be evaluated at all

Choose fallback behavior that aligns with your feature rollout strategy.

Test the Dependency

Use the Test flag section to verify your dependency works correctly. Enter test user properties or use the Preview feature to see how the flag behaves under different prerequisite conditions.

Test with different user segments to ensure dependencies work across all target audiences.

Save and Deploy

Click Save changes to apply the dependency configuration. The dependent flag will now only evaluate based on your configured prerequisites. Monitor the flag performance in the Insights section.

Document your flag dependencies to help team members understand the relationship between flags.

Common Issues & Troubleshooting

Dependent flag not respecting prerequisites

Check that the prerequisite flag is properly enabled and targeting the same user segments. Verify the dependency condition logic matches your intended behavior.

Circular dependency error

Review your flag dependency chain to ensure no flags depend on each other in a loop. Use the Dependencies visualization to identify circular references and restructure accordingly.

Flag dependency not visible in dashboard

Ensure you have the latest PostHog version and refresh your browser. Check that you have sufficient permissions to view and modify flag dependencies in your project settings.

Performance issues with complex dependencies

Limit dependency chains to 2-3 levels deep and consider consolidating related flags. Use Flag insights to monitor evaluation times and optimize dependency structures.

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