Flag Dependencies

How Dependencies Work#

When a flag has dependencies, all of them are checked first. If any dependency is not met, the dependent flag is served off (enabled: false, the flag's off value) with reason PREREQUISITE_FAILED.

{
  "dependencies": [
    { "flagKey": "dark_mode" },
    { "flagKey": "beta_features", "expectedValue": true }
  ]
}

In this example, the flag is only enabled if both dark_mode is enabled AND beta_features evaluates to true.

• Without expectedValue, a dependency is met when that flag is served on for the user.
• With expectedValue, it is met when the value served to the user equals it.
• A dependency is evaluated in the same environment and for the same user as the flag itself. So a dependency with a 20% rollout is met only for the users inside that 20%.

Evaluation Order#

Dependencies are resolved recursively during evaluation:

Evaluating flag "premium_dark_theme":
  1. Check dependency: "dark_mode"
     → dark_mode is enabled ✓
  2. Check dependency: "beta_features"
     → beta_features is enabled ✓
     → expectedValue matches ✓
  3. All dependencies met → continue evaluation
  4. Check targeting rules, rollout, variants...
  5. Return result

In code you can see the outcome in the reason:

// Server SDK
const d = flags.getDetail('premium_dark_theme', { userId: 'user-123' }, false);
if (d.reason === 'PREREQUISITE_FAILED') {
  // dark_mode or beta_features is not met for this user
}

Use Cases#