> ## Documentation Index
> Fetch the complete documentation index at: https://docs.softlaunch.so/llms.txt
> Use this file to discover all available pages before exploring further.

# SDK overview

> Choose an SDK and learn the API shared across all of them.

Softlaunch SDKs load your configuration snapshot and evaluate flags locally. Pick the SDK that matches where your code runs.

## Client vs. server

<CardGroup cols={2}>
  <Card title="Client SDKs" icon="globe">
    Run in browsers, mobile apps, and other public clients. Use a **client key** (`slc_`), which serves an obfuscated configuration.
  </Card>

  <Card title="Server SDKs" icon="server">
    Run in trusted backends. Use a **server key** (`sls_`), which reads the full configuration. Keep it secret.
  </Card>
</CardGroup>

## Available SDKs

<CardGroup cols={2}>
  <Card title="React" icon="react" href="/sdks/react">
    `@softlaunch/react` — a provider and hooks for React apps.
  </Card>

  <Card title="JavaScript" icon="js" href="/sdks/javascript">
    `@softlaunch/js` — a client for any JavaScript runtime.
  </Card>
</CardGroup>

More SDKs are on the way:

<CardGroup cols={3}>
  <Card title="Node.js" icon="node-js">
    Coming soon
  </Card>

  <Card title="Go" icon="golang">
    Coming soon
  </Card>

  <Card title="Python" icon="python">
    Coming soon
  </Card>
</CardGroup>

## A shared API

Every SDK exposes one typed accessor per [flag type](/concepts/feature-flags). The arguments are the same everywhere:

```ts theme={null}
get<Type>Flag(flagKey, subjectKey, attributes, defaultValue);
```

| Argument       | Description                                                     |
| -------------- | --------------------------------------------------------------- |
| `flagKey`      | The key of the flag to evaluate.                                |
| `subjectKey`   | A stable identifier for the user or entity.                     |
| `attributes`   | Key–value attributes used for [targeting](/concepts/targeting). |
| `defaultValue` | Returned while loading, or if the flag is missing or mistyped.  |

The typed accessors are `getBooleanFlag`, `getStringFlag`, `getIntegerFlag`, `getNumericFlag`, and `getJsonFlag` (the React SDK exposes the same set as hooks: `useBooleanFlag`, and so on).

<Note>
  SDKs stay subscribed after the first load. When you change a flag, connected SDKs receive the update in real time and re-evaluate.
</Note>