> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.getunleash.io/api/client-api-overview/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.getunleash.io/_mcp/server.

# Client API overview

> The Client API is used by backend SDKs to fetch feature flag configurations and report metrics to Unleash.

The Client API is designed for [backend SDKs](/sdks/node) and [Unleash Edge](/unleash-edge) to fetch feature flag configurations. This API returns all [feature flags](/concepts/feature-flags) and [activation strategies](/concepts/activation-strategies) for server-side evaluation.

**Base path**: `<your-unleash-url>/api/client`

**Primary use**: Backend services fetch complete flag configurations to evaluate flags server-side with full [activation strategy](/concepts/activation-strategies) logic and [constraints](/concepts/unleash-context).

## Authentication

Use [backend tokens](/concepts/api-tokens-and-client-keys) for authentication. These tokens can be scoped to specific [projects](/concepts/projects) and [environments](/concepts/environments). Backend tokens must remain secret and should never be exposed in client-side code.

To create a backend token, go to **Admin settings > Access control > API access > New API token**

## Available endpoints

| Endpoint                             | Method | Description                                                            |
| ------------------------------------ | ------ | ---------------------------------------------------------------------- |
| `/api/client/features`               | GET    | Fetch all [feature flags](/concepts/feature-flags) and configurations. |
| `/api/client/features/{featureName}` | GET    | Fetch specific feature flag configuration.                             |
| `/api/client/metrics`                | POST   | Report flag usage metrics.                                             |
| `/api/client/metrics/custom`         | POST   | Report [impact metrics](/concepts/impact-metrics).                     |
| `/api/client/register`               | POST   | Register SDK instance.                                                 |

## Using with Unleash Edge

[Unleash Enterprise Edge](/unleash-edge) uses the Client API to stay synchronized with your Unleash instance. Edge provides:

* Reduced latency for distributed applications.
* Built-in caching and fallback.
* Lower load on your main Unleash instance.
* Frontend API endpoint support.

> The Client API is used by backend SDKs to fetch feature flag configurations and report metrics to Unleash.