One of the most important aspects of the architecture to understand is that feature toggles _are evaluated in a client SDKs_ which runs as part of your application. This makes toggle evaluations super-fast (_we talk nano-seconds_), scalable and resilient against network disturbances. In order to achieve this Unleash compromises a small update-delay when you change your toggle configurations until it is fully propagated to your application (in terms of seconds and is configurable).
- **Unleash API** - The service holding all feature toggles and their configurations. Configurations declare which activation strategies to use and which parameters they should get. [API documentation](/api)
- **Unleash Admin UI** - The dashboard used to manage feature toggles, define new strategies, look at metrics, etc. [Create your first feature toggle](user_guide/create-feature-toggle.md)
- **Unleash SDK** - Used by clients to check if a feature is enabled or disabled. The SDK also collects metrics and sends them to the Unleash API. [See all our SDKs](sdks/index.md)
- **Unleash Proxy** - Sits between frontend/native applications and the Unleash API. Ensures high performance and that you don't expose the full feature toggle configuration to end-users. [Read more about Unleash Proxy](sdks/unleash-proxy.md)
To be super fast (_we talk nano-seconds_), the [client SDK](sdks/index.md) caches all feature toggles and their current configuration in memory. The activation strategies are also implemented in the SDK. This makes it really fast to check if a toggle is on or off because it is just a simple function operating on local state, without the need to poll data from the database.
