--- title: 'Environment variables' --- You can use environment variables in Storybook to change its behavior in different “modes”. If you supply an environment variable prefixed with `STORYBOOK_`, it will be available in `process.env` when using Webpack, or `import.meta.env` when using the Vite builder: ```shell STORYBOOK_THEME=red STORYBOOK_DATA_KEY=12345 npm run storybook ``` Do not store any secrets (e.g., private API keys) or other types of sensitive information in your Storybook. Environment variables are embedded into the build, meaning anyone can view them by inspecting your files. Then we can access these environment variables anywhere inside our preview JavaScript code like below: You can also access these variables in your custom ``/`` using the substitution `%STORYBOOK_X%`, for example: `%STORYBOOK_THEME%` will become `red`. If using the environment variables as attributes or values in JavaScript, you may need to add quotes, as the value will be inserted directly, for example: ``. ### Using .env files You can also use `.env` files to change Storybook's behavior in different modes. For example, if you add a `.env` file to your project with the following: ``` STORYBOOK_DATA_KEY=12345 ``` Then you can access this environment variable anywhere, even within your stories: #### With Vite Out of the box, Storybook provides a [Vite builder](../builders/vite.md), which does not output Node.js globals like `process.env`. To access environment variables in Storybook (e.g., `STORYBOOK_`, `VITE_`), you can use `import.meta.env`. For example: You can also use specific files for specific modes. Add a `.env.development` or `.env.production` to apply different values to your environment variables. You can also pass these environment variables when you are [building your Storybook](../sharing/publish-storybook.md) with `build-storybook`. Then they'll be hardcoded to the static version of your Storybook. ### Using Storybook configuration Additionally, you can extend your Storybook configuration file (i.e., [`.storybook/main.js|.ts`](../configure/index.md#configure-story-rendering)) and provide a configuration field that you can use to define specific variables (e.g., API URLs). For example: When Storybook loads, it will enable you to access them in your stories similar as you would do if you were working with an `env` file: ### Using environment variables to choose the browser Storybook allows you to choose the browser you want to preview your stories. Either through a `.env` file entry or directly in your `storybook` script. The table below lists the available options: | Browser | Example | | -------- | -------------------- | | Safari | `BROWSER="safari"` | | Firefox | `BROWSER="firefox"` | | Chromium | `BROWSER="chromium"` | By default, Storybook will open a new Chrome window as part of its startup process. If you don't have Chrome installed, make sure to include one of the following options, or set your default browser accordingly. ## Troubleshooting ### Environment variables are not working If you're trying to use framework-specific environment variables (e.g.,`VUE_APP_`), you may run into issues primarily due to the fact that Storybook and your framework may have specific configurations and may not be able to recognize and use those environment variables. If you run into a similar situation, you may need to adjust your framework configuration to make sure that it can recognize and use those environment variables. For example, if you're working with a Vite-based framework, you can extend the configuration file and enable the [`envPrefix`](https://vitejs.dev/config/shared-options.html#envprefix) option. Other frameworks may require a similar approach.