Documentation

Quick Start

Get up and running with FlagFeature in under 5 minutes.

1. 1Register an account at FlagFeature
2. 2Create a new project from the dashboard
3. 3Generate an API key in Settings → API Keys
4. 4Create your first feature flag
5. 5Call the SDK evaluate endpoint from your app

SDK Usage

Evaluate feature flags from any language using our REST API.

Query Parameters

const res = await fetch(
  'https://your-app.vercel.app/api/sdk/evaluate?projectId=PROJ_ID&environment=production&userId=user_123',
  { headers: { 'x-api-key': 'YOUR_API_KEY' } }
)
const { flags } = await res.json()

if (flags.new_feature) {
  // show new feature
}

React Integration

Use this custom hook to evaluate flags in any React component.

import { useEffect, useState } from 'react'

export function useFlags(userId: string) {
  const [flags, setFlags] = useState<Record<string, boolean>>({})

  useEffect(() => {
    fetch(
      `/api/sdk/evaluate?projectId=PROJ_ID&environment=production&userId=${userId}`,
      { headers: { 'x-api-key': process.env.NEXT_PUBLIC_FLAG_API_KEY! } }
    )
      .then(r => r.json())
      .then(data => setFlags(data.flags))
  }, [userId])

  return flags
}

// In your component:
const flags = useFlags(user.id)
if (flags.dark_mode) return <DarkTheme />

Percentage Rollouts

Gradually roll out features to a percentage of your users.

• →Set rollout from 0% to 100% using the slider on the project page
• →Pass a userId to the SDK for deterministic, sticky rollouts
• →The same user always gets the same flag result — no flickering
• →Increasing rollout from 50% to 75% keeps the original 50% cohort in
• →Without a userId, rollout is random per request (not sticky)

Environments

Each project has three environments by default.

API Reference

All endpoints require a Bearer JWT token unless noted.