Server TypeScript SDK

The server TypeScript SDK is built for trusted server-side applications. It uses secret server runtime keys, keeps the latest snapshot in memory, evaluates locally, and returns caller-provided defaults before the first snapshot is ready. Use the Browser SDK or React SDK for publishable client-key evaluation in browser code.

Create a client

Create one client per runtime key and reuse it for the lifetime of the process. Choose streaming for near-instant invalidation, or polling when a long-lived connection is not practical.

import { FeatureGateClient } from "@featuregate/server";

export const featuregate = new FeatureGateClient({
runtimeApiKey: process.env.FEATUREGATE_RUNTIME_KEY!,
syncMode: "streaming",
});

await featuregate.waitForReady({ timeoutMs: 2_000 });

Evaluate flags

Every evaluation takes an explicit default, so a call site is well-defined even before the first snapshot arrives or if a flag is removed.

const enabled = featuregate.isEnabled("new-checkout", {
defaultValue: false,
attributes: {
  user: { id: "user_123" },
  account: { plan: "pro" },
},
});

Testing & offline

For tests and local development, use offline and overrides so your app does not need a network call just to run a unit test. Call close() on shutdown to release the sync connection.

Next steps