Create Your First Flag

This guide walks through creating a feature flag, enabling it per environment, adding targeting rules, and evaluating it from your application.

Step 1: Register and Set Up

After installing FeatureSignals, register at http://localhost:3000. Registration automatically creates:

• Your user with owner role
• A default organization
• A Default Project with environments: dev, staging, production

Step 2: Create a Flag

Navigate to Flags and click Create Flag.

Field	Value	Description
Key	dark-mode	Unique identifier used in code
Name	Dark Mode	Human-readable label
Type	boolean	Flag type (boolean, string, number, json, ab)
Default Value	false	Returned when the flag is disabled

The flag key is immutable after creation and is what your SDKs reference.

Step 3: Enable Per Environment

Flags are disabled by default in all environments. To enable:

1. Open the flag detail page
2. Select the dev environment tab
3. Toggle Enabled to ON
4. The flag now returns true for all users in dev

You can enable different configurations per environment — for example, ON in dev, OFF in production.

Step 4: Add Targeting Rules

Targeting rules let you return specific values based on user attributes:

1. In the flag's dev environment, click Add Rule
2. Configure:
   • Condition: country equals US
   • Value: true
   • Percentage: 100% (10000 basis points)
3. Save

Now only users with country: "US" in their context get true. Others fall through to the default.

Step 5: Evaluate from Code

import { FeatureSignalsClient } from '@featuresignals/node';

const client = new FeatureSignalsClient('fs_srv_...', {
  envKey: 'dev',
  baseURL: 'http://localhost:8080',
});

await client.waitForReady();

// User from US gets targeting rule match
const usUser = client.boolVariation('dark-mode', { key: 'user-1', attributes: { country: 'US' } }, false);
// → true

// User from UK falls through to default
const ukUser = client.boolVariation('dark-mode', { key: 'user-2', attributes: { country: 'UK' } }, false);
// → false (flag default)

Evaluation Context

The key field is required and uniquely identifies the user. It's used for percentage rollouts and A/B variant assignment via consistent hashing.

Step 6: Gradual Rollout

Instead of enabling for all users, do a percentage rollout:

1. Set Percentage Rollout to 2500 (25%)
2. Save

Now 25% of users (deterministically based on their key) see true, and the rest see the default value.

Understanding Evaluation Reasons

Each evaluation returns a reason explaining why a value was chosen:

Reason	Meaning
DISABLED	Flag is off in this environment
TARGETED	Matched a targeting rule at 100%
ROLLOUT	Matched via percentage rollout
FALLTHROUGH	Flag enabled but no rules matched
NOT_FOUND	Flag key doesn't exist
PREREQUISITE_FAILED	A prerequisite flag condition wasn't met
MUTUALLY_EXCLUDED	Another flag in the mutex group won
VARIANT	A/B experiment variant assigned

Next Steps

• Targeting & Segments — advanced targeting with reusable segments
• A/B Experimentation — run experiments with variants
• Kill Switch — emergency disable