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Front-end API access


The Unleash front-end API was released in Unleash 4.18. You can read more in the Unleash 4.18 release blog post.

The Unleash front-end API offers a simplified workflow for connecting a client-side (front-end) applications to Unleash. It provides the exact same API as Unleash edge and the Unleash proxy - deprecated. The front-end API is a quick and easy way to add Unleash to single-page applications and mobile apps.

Compared to using Unleash Edge, using the Unleash front-end API has both benefits and drawbacks. The benefits are:

  • You don't need to configure and run Unleash Edge. The front-end API is part of Unleash itself and not an external process. All clients will work exactly the same as they would with Unleash Edge.

On the other hand, using the front-end API has the following drawbacks compared to using Unleash Edge:

  • It can't handle a large number of requests per second. Because the front-end API is part of Unleash, you can't scale it horizontally the way you can scale Unleash Edge.
  • It sends client details to your Unleash instance. Unleash only stores these details in its short-term runtime cache, but this can be a privacy issue for some use cases.

These points make the Unleash front-end API best suited for development purposes and applications that don’t receive a lot of traffic, such as internal dashboards. However, because the API is identical to the Unleash Edge API, you can go from one to the other at any time. As such, you can start out by using the front-end API and switch to using Unleash Edge when you need it.

Using the Unleash front-end API

When using the front-end API in an SDK, there's three things you need to configure.

Front-end API tokens

As a client-side API, you should use a front-end API token to interact with it. Refer to the how to create API tokens guide for steps on how to create API tokens.

Cross-origin resource sharing (CORS) configuration

You need to allow traffic from your application domains to use the Unleash front-end API with web and hybrid mobile applications. You can update the front-end API CORS settings from the Unleash UI under admin > CORS or by using the API.


The client needs to point to the correct API endpoint. The front-end API is available at <your-unleash-instance>/api/frontend.

API token

You can create appropriate token, with type FRONTEND on <YOUR_UNLEASH_URL>/api/admin/create-token page or with a request to /api/admin/api-tokens. See our guide on how to create API tokens for more details.

Refresh interval for tokens

Internally, Unleash creates a new Unleash client for each token it receives. Each client is configured with the project and environment specified in the token.

Each client updates its feature flag configuration at a specified refresh interval plus a random offset between 0 and 10 seconds. By default, the refresh interval is set to 10 seconds. The random offset is used to stagger incoming requests to avoid a large number of clients all querying the database simultaneously. A new, random offset is used for every update.

The refresh interval is specified in milliseconds and can be set by using the FRONTEND_API_REFRESH_INTERVAL_MS environment variable or by using the frontendApi.refreshIntervalInMs configuration option in code.