Managing environment variables

Managing environment variables

Environment variables can be used to provide your Flutter app with environment-specific configuration. They allow you to keep configuration values separate from your codebase, improving flexibility when deploying your backend to different environments.


Environment variables are only accessible in your backend.

Creating environment variables

To define environment variables and their values, create a config folder inside the celest folder, and then create a .env file inside it. When you run the celest start command in your console, your environment variables will be read from the .env file and made available to your Celest backend locally.

Using environment variables with Celest Functions

To provide a function access to an environment variable when it runs, pass it as a parameter and annotate with the variable definition. In the following code snippet, a greeting service URL will be securely injected by the server when your function starts.


Annotated parameters (like greetingUrl) will not appear in the code-generated Celest client, but can be used in your backend when unit testing and mocking (see Testing your functions).

import 'package:http/http.dart' as http;
// Make sure to import the `env` type, which is generated by Celest.
import '../generated/resources.dart';
Future<String> sayHello(
  String name, {
  @env.greetingUrl required Uri greetingUrl,
}) async {
  // Call an external greeting service.
  final response = await
    body: jsonEncode({
      'name': name,
  if (response.statusCode != 200) {
    throw Exception("An error occured calling the greeting service");
  return response.body;

When the Celest Function runs, it will automatically have access to the environment variable. Its value is stored securely and is never hard-coded in your codebase or in the deployed Celest Function.

Next steps

You have now learned about the flows available for updating, retreiving, and deleting environment variables in your Celest project. You can follow additional guides to learn more about testing your functions, and installing 3rd party Dart packages.