# Environment variables

You can define environment variables and use them in `redocly.yaml`, and Markdown and React pages in the project.
Environment variables are used during both build and run time for the project.
By default, environment variables are not available in the browser.
To access environment variables in React or Markdown pages, you have to prefix them with `PUBLIC_`.

## Define environment variables

Define environment variables using one of the following ways:

- Create `.env` file in the root of the project
- Use the shell (in other words, in your local environment, CI)
- Add them individually on the **Settings** page for the project


### .env files

Example `.env` file can look like this:


```text
PUBLIC_CUSTOM_VARIABLE=Hello
PUBLIC_IS_PRODUCTION=true
PUBLIC_BUILD_NUMBER=50
```

Using the `REDOCLY_ENV` variable, you can set up different environments and use separate `.env` files like `.env.production`, `.env.development`, and `.env.preview` based on your needs.

When hosting your project at Redocly, we will automatically set the proper `REDOCLY_ENV` variable:

- For production builds, the `REDOCLY_ENV` variable will be set to `"production"`
- For previews, the `REDOCLY_ENV` variable will be set to `"preview"`


### Settings page

You can also add environment variables individually through the Redocly interface:

1. Once logged in to Redocly, select the project.
2. Select **Settings** > **Environment variables**.
3. Select **Add environment variable**.
4. Enter the Environment variable name and value.
5. If the variable is a secret, select the secret checkbox to store it in an encrypted format and exclude it from the logs.


## Usage

Do not use environment variables with sensitive information like passwords or API keys on the pages because all users of the project can see them.

### `redocly.yaml`

To use environment variables in `redocly.yaml`, use the curly brace syntax `{{ process.env.<env_var_name> }}`.

For example:


```yaml redocly.yaml
logo:
  srcSet: '{{ process.env.LIGHT_LOGO_PATH }} light, {{ process.env.DARK_LOGO_PATH }} dark'
  altText: Redocly logo
  link: '/'
navbar:
  items:
    - page: index.md
      label: '{{ process.env.HOME_LABEL }}'
    - page: config/index.md
      label: Config
```

Environment variables in `redocly.yaml` only support string values.

### React

To use environment variables in your React code, refer to them using the following syntax: `process.env.<env_var_name>`

The following is an example of using an environment variable in a Typescript file:


```typescript
import * as React from 'react';


export default function () {

  const buildNumber: number = parseInt(process.env.PUBLIC_BUILD_NUMBER || '')

  return (
    <div>
        <h1>My custom variable value is {process.env.PUBLIC_CUSTOM_VARIABLE}</h1>
        <h2>Is this running in production? - {process.env.PUBLIC_IS_PRODUCTION}</h2>
        <h3>Is build number high? - {buildNumber > 40 ? 'Yes' : 'No'}</h3>
    </div>
  );
```

Environment variables always have `String` type.
`PUBLIC_IS_PRODUCTION` and `PUBLIC_BUILD_NUMBER` from example above will become `"true"` and `"50"` when used in React components.
To get them in desired type, you'll have to do manual conversion.

### Markdown

In Markdown files, access environment variables using [Markdoc variables syntax](https://markdoc.dev/docs/variables) under `env` namespace:


```markdoc
# My custom variable is {% $env.PUBLIC_CUSTOM_VARIABLE %}
```

## Default environment variables

The following environment variables are available by default:

- `PUBLIC_REDOCLY_BRANCH_NAME`: The name of the branch that the project is built from


## Manage environment variables

You can manage environment variables through the **Settings** page in your project.

### Change an environment variable

1. Once logged in to Redocly, select the project.
2. Select **Settings** > **Environment variables**.
3. Hover over the environment variable you want to update.
4. Select the *Edit* icon next to the variable you want to change.
5. In the **Edit environment variable** dialog that opens, make changes to your variable value select to make the variable secret.
6. Select **Save**.


### Remove an environment variable

1. Once logged in to Redocly, select the project.
2. Select **Settings** > **Environment variables**.
3. Select the *Delete* icon next to the variable you want to remove.
The variable is removed from the list immediately.


## Restrictions

When defining custom names, avoid commonly reserved environment variables, such as `HOME` and `PATH`, and those related to the Node environment such as `NODE_ENV`.

The `PUBLIC_` prefix is shared with the client side, and should not be used for any secrets.

The `REDOCLY_` prefix is reserved for future use by Redocly.

## Resources

- **[Markdoc variables syntax](https://markdoc.dev/docs/variables)** - Learn the syntax for using environment variables within Markdown content and templates
- **[Projects overview](/docs/realm/reunite/project/projects)** - Explore other project configuration options and settings available in Reunite