After App Check is enforced for a backend service, your app's features that
depend on that backend service won't run from `localhost` or from a
continuous integration (CI) environment because these environments don't qualify
as valid devices. To run your app in these environments during development and
testing, you need to create a debug build of your app that uses the
App Check *debug provider* instead of a production attestation provider.

> [!WARNING]
> **Warning:** **Keep your debug token and debug build private.** A valid debug token and the debug provider in your debug build allow access to your backend services from unverified devices. Do ***not*** commit your debug token to a public repository, and do ***not*** ship your debug token or debug build in production builds of your app. If a registered token is ever compromised, delete it immediately in the Firebase console.

## Use the debug provider on localhost

Here's how to use the debug provider while running your app from `localhost`
(for example, during local development):

> [!WARNING]
> **Warning:** Do ***not*** try to enable `localhost` debugging by adding `localhost` to the allowed domains for reCAPTCHA. Doing so would allow anyone to run your app from their local machines!

1. In your debug build, enable debug mode by setting
   `self.FIREBASE_APPCHECK_DEBUG_TOKEN` to `true` before you initialize
   App Check. For example:

   ### Web

   ```javascript
   self.FIREBASE_APPCHECK_DEBUG_TOKEN = true;
   initializeAppCheck(app, { /* App Check options */ });
   ```

   ### Web

   ```javascript
   self.FIREBASE_APPCHECK_DEBUG_TOKEN = true;
   firebase.appCheck().activate(/* site key or provider */);
   ```

   > [!NOTE]
   > **Note:** In Firebase Web SDK versions before v9, `self.FIREBASE_APPCHECK_DEBUG_TOKEN` is read at import time, and not at initialization/activation time. This required it to be set in `index.html` before the code bundle is loaded. To avoid this restriction, upgrade to v9.

2. Visit your web app locally and open the browser's developer tools. In the
   debug console, you'll see a debug token:

       AppCheck debug token: "123a4567-b89c-12d3-e456-789012345678".
       You will need to safelist it in the Firebase console for it to work.

3. Register your debug token with App Check:

   1. In the Firebase console, go to the **Security** \> **App Check** \>
      [**Apps** tab](https://console.firebase.google.com/project/_/appcheck/apps/?useAutoProject=true).

   2. Find your app, click the three-dot overflow menu
      (), and then select
      **Manage debug tokens**.

   3. Follow the on-screen instructions to register your debug token.

   ![Screenshot of the Manage Debug Tokens menu item in the Firebase console](https://firebase.google.com/static/docs/app-check/manage-debug-tokens.png)

After you register the token with App Check, your backend services will
accept it as valid.

This token allows access to your backend services without a valid device,
so it's crucial that you keep it private. Do ***not*** commit it to a
public repository or ship it in production builds of your app. If a
registered token is ever compromised, delete it immediately using
**Manage debug tokens** in the Firebase console.

This token is stored locally in your browser and will be used whenever you use
your app in the same browser on the same machine. If you want to use the
token in another browser or on another machine, set
`self.FIREBASE_APPCHECK_DEBUG_TOKEN` to the token string instead of `true`.

## Use the debug provider in a CI environment

Here's how to use the debug provider in a
continuous integration (CI) environment:

1. In the Firebase console, create a debug token:

   1. In the Firebase console, go to the **Security** \> **App Check** \>
      [**Apps** tab](https://console.firebase.google.com/project/_/appcheck/apps/?useAutoProject=true).

   2. Find your app, click the three-dot overflow menu
      (), and then select
      **Manage debug tokens**.

   3. Follow the on-screen instructions to create a new debug token.

   This token allows access to your backend services without a valid device,
   so it's crucial that you keep it private. Do ***not*** commit it to a
   public repository or ship it in production builds of your app. If a
   registered token is ever compromised, delete it immediately using
   **Manage debug tokens** in the Firebase console.

   ![Screenshot of the Manage Debug Tokens menu item](https://firebase.google.com/static/docs/app-check/manage-debug-tokens.png)
2. Add the debug token you just created to your CI system's secure key store
   (for example, GitHub Actions' [encrypted secrets](https://docs.github.com/en/actions/reference/encrypted-secrets)
   or Travis CI's [encrypted variables](https://docs.travis-ci.com/user/environment-variables/#defining-encrypted-variables-in-travisyml)).

3. If necessary, configure your CI system to make your debug token available
   within the CI environment as an environment variable. Name the variable
   something like `APP_CHECK_DEBUG_TOKEN_FROM_CI`.

4. In your debug build, enable debug mode by setting
   `self.FIREBASE_APPCHECK_DEBUG_TOKEN` to the value of the debug token
   environment variable before you import App Check. For example:

   ### Web

   ```javascript
   self.FIREBASE_APPCHECK_DEBUG_TOKEN = process.env.APP_CHECK_DEBUG_TOKEN_FROM_CI;
   initializeAppCheck(app, { /* App Check options */ });
   ```

   ### Web

   ```javascript
   self.FIREBASE_APPCHECK_DEBUG_TOKEN = process.env.APP_CHECK_DEBUG_TOKEN_FROM_CI;
   firebase.appCheck().activate(/* site key or provider */);
   ```

When your app runs in a CI environment, your backend services will accept
the token it sends as valid.