Your first feature flag

Overview

This topic explains how to create feature flags in LaunchDarkly. You can use feature flags in any aspect of your application, from the customer-facing user interface (UI) to the backend.

The procedures in this topic assume that you have already configured a LaunchDarkly SDK and are ready to use the LaunchDarkly UI. For an example tutorial of how to configure a LaunchDarkly SDK, read Getting started: Configuring an SDK and creating a flag.

In the LaunchDarkly UI, you can create a new flag, clone and modify an existing flag to create new ones, and set default values for flags.

Creating a feature flag

You can create and modify feature flags from the flags list. To learn more, read The flags list.

To create a feature flag:

1. Navigate to the flags list.
2. Click Create flag. The "Create a feature flag" panel appears:

3. Enter a unique, human-readable Name.
4. Enter a unique flag Key. You'll use this key to reference the flag in your code. A suggested key auto-populates from the name you enter, but you can customize it if you wish.

5. (Optional) Enter a Description of the flag. A brief, human-readable description helps your account members understand what the flag is for.
6. (Optional) Click into the Tags menu and choose one or more tags for your flag.

7. (Optional) In the "Client-side SDK flag availability" section, check the SDKs using Mobile Key and/or SDKs using client-side ID boxes to designate which SDKs the flag should be available to. To learn more, read Making flags available to client-side and mobile SDKs.
8. Choose an option in the Flag variations menu. To learn more, read Flag variations.
9. (Optional) Specify details for your Variation. To learn more, read Understanding multivariate flags.
10. (Optional) Change the Default values for the flag's on and off states. To learn more, read Setting default values.
11. (Optional) Select the This is a permanent flag box.
12. Click Save flag.

You just created a feature flag. It appears in the list.

Making flags available to client-side and mobile SDKs

By default, flags are only available to server-side SDKs. When you create a flag, you can choose to expose the flag to SDKs which use client-side IDs, SDKs which use mobile keys, or both. If you're using a client-side or mobile SDK, you must expose your feature flags in order for the client-side or mobile SDKs to evaluate them.

Here is an image of the "Client-side SDK availability" section:

If an SDK tries to evaluate a feature flag that is not available, the user will receive the default value for that flag.

To make all of a project's flags available to client-side or mobile SDKs by default, check the SDKs using Client-side ID or SDKs using Mobile key checkboxes in your project Settings.

To learn more, read Client-side and server-side SDKs.

Configuring the same flag in different environments

All environments within a project have the same set of feature flags. When you create a new feature flag, it is created in every environment in your LaunchDarkly project. That flag is scoped to your entire project.

Flag configuration settings are specific to each environment. The changes you make in one environment do not apply to the same flag in any other environment. If you want to, you can configure the same flag in a unique way for every environment you have.

To configure a flag in a different environment:

1. Navigate to the flags list.
2. Click the environment name in the top left corner. The "Switch environment" menu appears:

3. Search for the environment you wish to switch to and click on it, or choose it from the list. The flags list for the new environment appears.

4. Find the flag you wish to modify and make whatever changes you like.

Setting default values

When you create a feature flag, some of its variations are designated as default values. You can accept the defaults or change them. When you change default values and click Save flag, the flag is created across all environments in your project with the new variations set as its default on and off values.

To learn more about default flag values, read Changing default flag values.

Here is a screenshot of flag creation panel:

Cloning flags

You can create new flags by cloning existing flags. When you clone a flag, LaunchDarkly makes a new flag and copies the original flag's targeting configuration for all environments, including default values and whether the flag is toggled on or off. You can then modify the clone's configuration if needed.

To clone a flag:

1. Navigate to the flags list.
2. Find the flag you wish to clone and click its name. The flag detail page appears:

3. Click the flag's Settings tab.
4. Click Clone this flag.

5. The "Clone feature flag" panel appears:

6. Enter a unique, human-readable Name.
7. Enter a unique flag Key. You'll use this key to reference the flag in your code. A suggested key auto-populates from the name you enter, but you can customize it if you wish.
8. (Optional) Enter a Description of the flag. A brief, human-readable description helps your account members understand what the flag is for.
9. (Optional) Click into the Tags menu and choose one or more tags for your flag.

10. Click Save flag. You are taken to the new flag's details page.

The new flag also appears in the flags list, where you can search for it or access it any time.