Flags SDK

The feature flags toolkit

Flags SDK is a free, open-source library for using feature flags in Next.js and SvelteKit.

Try the Flags SDK

Set persistent flags for this page

enable-dithered-hero-flagKeep it dithered

swap-hero-textToggle between headline options for A/B testing

enable-banner-flagFull-width callout at the top

Using flags as code

The SDK sits between your application and the source of your flags, helping you follow best practices and keep your website fast.

Works with any provider

Use any flag provider, or none at all. Flexible integrations for your projects.

Effortless integration

Integrate with App Router, Pages Router, and Routing Middleware.

Release strategically

Ideal for A/B testing and controlled rollouts. Experiment with confidence.

Effortless setup

With a simple declarative API to define and use your feature flags.

Read the Docs

import { flag } from 'flags/next';
export const exampleFlag = flag({
  key: 'example-flag',
  decide() {
    return Math.random() > 0.5;
  },
});

Declaring a flag

import { exampleFlag } from "../flags";
export default async function Page() {
  const example = await exampleFlag();
  return <div>Flag {example ? "on" : "off"}</div>;
}

Using a flag