> ## Documentation Index
> Fetch the complete documentation index at: https://docs.solute.so/llms.txt
> Use this file to discover all available pages before exploring further.

# Feature Flags Endpoint

> GET /api/feature-flags - Serve feature flags for a user

## GET /api/feature-flags

Fetches feature flags and experiments for a user. This endpoint is called by the SDK to get the current state of feature flags.

## Request

### Headers

<ParamField header="X-Api-Key" type="string" required>
  Your API key
</ParamField>

### Query Parameters

<ParamField query="userId" type="string">
  The user's ID (if user is identified)
</ParamField>

<ParamField query="anonymousId" type="string">
  The anonymous ID
</ParamField>

<ParamField query="userProperties" type="string">
  JSON-encoded user properties for targeting (optional)
</ParamField>

### Example Request

```bash theme={null}
curl -X GET "https://api.solute.dev/api/feature-flags?userId=user_123&anonymousId=anon_456" \
  -H "X-Api-Key: your_api_key"
```

## Response

### Success Response

<ParamField body="flags" type="object" required>
  Object mapping flag keys to flag objects
</ParamField>

<ParamField body="experiments" type="object">
  Object mapping experiment keys to experiment objects
</ParamField>

<ParamField body="timestamp" type="string" required>
  ISO 8601 timestamp
</ParamField>

### Flag Object

<ParamField body="key" type="string" required>
  Flag key
</ParamField>

<ParamField body="enabled" type="boolean" required>
  Whether the flag is enabled
</ParamField>

<ParamField body="variant" type="string">
  Assigned variant (for experiments)
</ParamField>

<ParamField body="value" type="boolean | string | number | object">
  Flag value
</ParamField>

<ParamField body="rolloutPercentage" type="number">
  Rollout percentage (0-100)
</ParamField>

### Experiment Object

<ParamField body="key" type="string" required>
  Experiment key
</ParamField>

<ParamField body="name" type="string" required>
  Experiment name
</ParamField>

<ParamField body="variants" type="Array<{ key: string; value: any }>" required>
  Available variants
</ParamField>

<ParamField body="assignedVariant" type="string">
  Assigned variant for this user
</ParamField>

<ParamField body="status" type="'draft' | 'running' | 'paused' | 'completed'" required>
  Experiment status
</ParamField>

### Example Response

```json theme={null}
{
  "flags": {
    "new-checkout-flow": {
      "key": "new-checkout-flow",
      "enabled": true,
      "variant": "variant-b",
      "value": true,
      "rolloutPercentage": 50
    },
    "show-ai-assistant": {
      "key": "show-ai-assistant",
      "enabled": false,
      "value": false
    }
  },
  "experiments": {
    "pricing-test": {
      "key": "pricing-test",
      "name": "Pricing Page A/B Test",
      "variants": [
        { "key": "control", "value": "original" },
        { "key": "variant-a", "value": "new-design" }
      ],
      "assignedVariant": "variant-a",
      "status": "running"
    }
  },
  "timestamp": "2025-01-15T10:30:00Z"
}
```

## Feature Flag Evaluation

### Consistent Hashing

For percentage-based rollouts, use consistent hashing to ensure the same user always gets the same variant:

```typescript theme={null}
function assignVariant(userId: string, flagKey: string, rolloutPercentage: number): boolean {
  const hash = djb2Hash(`${userId}:${flagKey}`);
  const userPercentage = (hash % 100) + 1; // 1-100
  return userPercentage <= rolloutPercentage;
}

function djb2Hash(str: string): number {
  let hash = 5381;
  for (let i = 0; i < str.length; i++) {
    hash = (hash * 33) ^ str.charCodeAt(i);
  }
  return hash >>> 0;
}
```

### Targeting Rules

Support targeting based on user properties:

* `equals`: Property equals value
* `not_equals`: Property does not equal value
* `contains`: Property contains value (for arrays/strings)
* `not_contains`: Property does not contain value
* `greater_than`: Property is greater than value
* `less_than`: Property is less than value
* `is_set`: Property exists
* `is_not_set`: Property does not exist

## Best Practices

<AccordionGroup>
  <Accordion title="Caching">
    Cache feature flags to reduce database load. Refresh cache when flags are updated.
  </Accordion>

  <Accordion title="Consistent Assignment">
    Use consistent hashing to ensure users always get the same variant.
  </Accordion>

  <Accordion title="Targeting">
    Evaluate targeting rules based on user properties to determine flag values.
  </Accordion>
</AccordionGroup>

## Related

<CardGroup cols={2}>
  <Card title="Events Endpoint" icon="chart-line" href="/backend-api/events" />

  <Card title="Identify Endpoint" icon="user" href="/backend-api/identify" />
</CardGroup>