OpenFeature

OpenFeature is the open standard for feature flag evaluation, and the openfeature driver lets flags use any OpenFeature provider: LaunchDarkly, Flagsmith, Unleash, PostHog, Vercel Flags and others. Your flags and targeting rules stay in your tool. Pick it when you already have a flag tool, or want to keep the choice open.

flags:
  driver: openfeature

Before you start

1. Have an account with a flag tool that offers an OpenFeature provider for your runtime.
2. Create the flags and targeting rules there, and store the tool's SDK key in your secrets manager.

Configure

flags:
  driver: openfeature
  # [to be decided] how the provider is named and its key passed, as secret:FLAGS_SDK_KEY (suggested name)

Use it

import { auth, flags } from "mainsdk";

export async function GET(req: Request) {
  const session = await auth.require(req);
  const useNew = await flags.enabled("new-checkout", { for: session.user });
  return Response.json({ checkout: useNew ? "new" : "classic" });
}

Local development and testing

createTestApp() from @mainsdk/testing runs flags on an in-memory fake, so tests reach no flag provider, and chaos.on("flags", { outage: true }) simulates the provider being down. Helpers to set a flag on the fake arrive with the spec.

What MainSDK adds on top

• Flags and targeting stay in your tool; MainSDK does not copy them out.
• One call, flags.enabled() or flags.value(), whatever the tool.

See Feature flags.

Limits and notes

Planned driver, not in a spec yet (phase 1). A flag is not a permission: decide who may do what with Permissions. Keep personal data out of flag names and values.

Swap to or from it

flags:
  driver: openfeature   # was posthog

Your calls stay the same; recreate the flags in the new tool.

FAQ

Do I have to move off my flag tool? No. That is the point of the OpenFeature driver.

Next

• Feature flags and Runtime settings
• PostHog and Vercel