---
title: LaunchDarkly
---

# LaunchDarkly



The [LaunchDarkly](https://launchdarkly.com/) provider contains support for LaunchDarkly's feature flags.

The `@flags-sdk/launchdarkly` package provides

* An [adapter](#provider-instance) for loading flags from LaunchDarkly.
* A `getProviderData` function for use with the Flags Explorer

<LearnMore icon="arrow" href="/providers">
  Learn more about Adapters
</LearnMore>

<LearnMore icon="arrow" href="https://vercel.com/docs/flags/flags-explorer" target="_blank">
  Learn more about the Flags Explorer
</LearnMore>

***

## Setup

The LaunchDarkly provider is available in the `@flags-sdk/launchdarkly` module. Install it with

```bash
npm install @flags-sdk/launchdarkly
```

***

## Provider Instance

Import the default adapter instance `ldAdapter` from `@flags-sdk/launchdarkly`:

```ts
import { ldAdapter } from '@flags-sdk/launchdarkly';
```

If you need a customized setup, you can import `createLaunchDarklyAdapter` from `@flags-sdk/launchdarkly` and create an adapter instance with your settings:

```ts
import { createLaunchDarklyAdapter } from '@flags-sdk/launchdarkly';

const customLdAdapter = createLaunchDarklyAdapter({
  projectSlug: process.env.LAUNCHDARKLY_PROJECT_SLUG,
  clientSideId: process.env.LAUNCHDARKLY_CLIENT_SIDE_ID,
  edgeConfigConnectionString: process.env.EDGE_CONFIG,
});
```

| Option key                   | Type     | Description                   |
| ---------------------------- | -------- | ----------------------------- |
| `projectSlug`                | `string` | LaunchDarkly project slug     |
| `clientSideId`               | `string` | LaunchDarkly client-side ID   |
| `edgeConfigConnectionString` | `string` | Edge Config connection string |

The default LaunchDarkly adapter configures itself based on the following environment variables:

* `LAUNCHDARKLY_CLIENT_SIDE_ID` *(required)* → `clientSideId`
* `LAUNCHDARKLY_PROJECT_SLUG` *(required)* → `projectSlug`
* `EDGE_CONFIG` *(required)* → `edgeConfigConnectionString`

***

## Identify Users

LaunchDarkly relies on an [LaunchDarkly Evaluation Context](https://launchdarkly.com/docs/home/observability/contexts) object to evaluate the flags for a given request.

Use the `identify` function to determine a LaunchDarkly Evaluation Context.

```ts
import { dedupe, flag } from "flags/next";
import type { Identify } from "flags";
import { ldAdapter, type LDContext } from "@flags-sdk/launchdarkly";

const identify = dedupe((async ({ headers, cookies }) => {
  // Your own logic to identify the user
  // Identifying the user should rely on reading cookies and headers only, and
  // not make any network requests, as it's important to keep latency low here.
  const user = await getUser(headers, cookies);

  return {
    key: user.userID,
    // ... other properties
  };
}) satisfies Identify<LDContext>);

export const exampleFlag = flag<boolean, LDContext>({
  key: "example-flag",
  identify,
  adapter: ldAdapter.variation(),
});
```

<LearnMore icon="arrow" href="/frameworks/next/dedupe">
  Learn more about `dedupe`
</LearnMore>

<LearnMore icon="arrow" href="/principles/evaluation-context">
  Learn more about `identify`
</LearnMore>

***

## Methods

The LaunchDarkly adapter provides a method for evaluating flags.

### `variation`

```ts
export const exampleFlag = flag<boolean, LDContext>({
  key: 'example-flag',
  identify,
  adapter: ldAdapter.variation(),
});
```

The `identify` function must return the [Evaluation Context](https://launchdarkly.com/docs/home/observability/contexts).

### `ldClient`

The adapter exposes the LaunchDarkly client it uses internally through the `ldClient` property.

```ts
import { ldAdapter } from '@flags-sdk/launchdarkly';

ldAdapter.ldClient;
```

***

## Edge Config

The LaunchDarkly adapter loads the configuration from [Edge Config](https://vercel.com/storage/edge-config).

Edge Config is a global, ultra-low latency store which uses active replication and is specifically designed for serving feature flag configuration.

The default LaunchDarkly adapter, exported as `ldAdapter`, will automatically connect to Edge Config required environment variabless are set.

***

## Caveats

### Initializing

The Flags SDK automatically initializes the LaunchDarkly client when a flag is evaluated.

If you want to initialize the LaunchDarkly client before the first flag is used, you can call `ldAdapter.ldClient.waitForInitialization()` manually.

```ts
import { ldAdapter } from '@flags-sdk/launchdarkly';

// Somewhere in your server-side code
await ldAdapter.ldClient.waitForInitialization();
```

### LaunchDarkly Vercel SDK

The adapter uses the [LaunchDarkly Vercel SDK](https://launchdarkly.com/docs/sdk/edge/vercel) (`@launchdarkly/vercel-server-sdk`) internally, which is designed for usage with Edge Config.

***

## Flags Explorer

View and override your LaunchDarkly flags using the [Flags Explorer](https://vercel.com/docs/flags/flags-explorer).

To make Flags Explorer aware of your LaunchDarkly flags, you need to provide a route which Flags Explorer will load your flags metadata from.

Use the `getProviderData` function  in your [Flags API endpoint](https://vercel.com/docs/workflow-collaboration/feature-flags/implement-flags-in-toolbar#creating-the-flags-api-endpoint) to load and emit your LaunchDarkly data. Accepts an `options` object with the following keys.

| Options key   | Type     | Description              |
| ------------- | -------- | ------------------------ |
| `apiKey`      | `string` | LaunchDarkly API Key     |
| `environment` | `string` | LaunchDarkly environment |
| `projectKey`  | `string` | LaunchDarkly project key |

```ts title="app/.well-known/vercel/flags/route.ts#next"
import { getProviderData, createFlagsDiscoveryEndpoint } from 'flags/next';
import { getProviderData as getLaunchDarklyProviderData } from '@flags-sdk/launchdarkly';
import { mergeProviderData } from 'flags';
import * as flags from '../../../../flags';

export const GET = createFlagsDiscoveryEndpoint(async (request) => {
  return mergeProviderData([
    getProviderData(flags),
    getLaunchDarklyProviderData({
      apiKey: process.env.LAUNCHDARKLY_API_KEY,
      projectKey: process.env.LAUNCHDARKLY_PROJECT_KEY,
      environment: process.env.LAUNCHDARKLY_ENVIRONMENT,
    }),
  ]);
});
```

## Read More

Read more about LaunchDarkly, Flags SDK, and the LaunchDarkly adapter.

* [Adapter Source Code](https://github.com/vercel/flags/tree/main/packages/adapter-launchdarkly)
* [Adapter Concept](/docs/adapters/supported-providers)
* [Precompute Concept](/principles/precompute)
* [LaunchDarkly Vercel SDK reference](https://launchdarkly.com/docs/sdk/edge/vercel)

<LearnMore icon="arrow" href="https://vercel.com/docs/flags/flags-explorer" target="_blank">
  Learn more about the Flags Explorer
</LearnMore>