This module provides access to environment variables set _dynamically_ at runtime and that are _publicly_ accessible.

|         | Runtime                                                                    | Buildtime                                                                |
| ------- | -------------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| Private | [`$env/dynamic/private`](/docs/kit/$env-dynamic-private) | [`$env/static/private`](/docs/kit/$env-static-private) |
| Public  | `$env/dynamic/public`                                                      | [`$env/static/public`](/docs/kit/$env-static-public)   |

Runtime environment variables are defined by the platform you're running on. For example if you're using [`adapter-node`](https://github.com/sveltejs/kit/tree/main/packages/adapter-node) (or running [`vite preview`](/docs/kit/cli)), this is equivalent to `process.env`.

**_Public_ access:**

- This module (and [`$env/static/public`](/docs/kit/$env-static-public)) _can_ be imported into client-side code.
- **Only** variables that begin with [`config.kit.env.publicPrefix`](/docs/kit/configuration#env) (which defaults to `PUBLIC_`) are included.

> [!NOTE] In `dev`, `$env/dynamic` includes environment variables from `.env`. In `prod`, this behavior will depend on your adapter.

> [!NOTE] To get correct types, environment variables referenced in your code should be declared (for example in an `.env` file), even if they don't have a value until the app is deployed:
>
> ```env
> MY_FEATURE_FLAG=
> ```
>
> You can override `.env` values from the command line like so:
>
> ```sh
> MY_FEATURE_FLAG="enabled" npm run dev
> ```

For example, suppose the buildtime environment variables were set like this:

```env
ENVIRONMENT=production
PUBLIC_BASE_URL=http://site.com
PUBLIC_VERSION=1
```

And then suppose at runtime the environment variables were set like this:

```env
ENVIRONMENT=production
PUBLIC_BASE_URL=http://not-the-same-site.com
PUBLIC_VERSION=9001
```

Assuming the `publicPrefix` is set to `PUBLIC_` and the `privatePrefix` is not set (the default behaviour), this is what would happen at runtime:

```ts
import { env } from '$env/dynamic/public';

console.log(env.ENVIRONMENT); // => undefined, not public
console.log(env.PUBLIC_BASE_URL); // => "http://not-the-same-site.com"
console.log(env.PUBLIC_VERSION); // => "9001"

import { ENVIRONMENT, PUBLIC_BASE_URL, PUBLIC_VERSION } from '$env/static/public';

console.log(env.ENVIRONMENT); // => undefined, throws error during build
console.log(env.PUBLIC_BASE_URL); // => "http://site.com"
console.log(env.PUBLIC_VERSION); // => "1"
```