AppSettings.json Generation

Fig can generate an appsettings.json file from your application's settings class, including encrypted secrets. This is useful for running applications in an offline mode without a Fig server.

Usage

Run your application with the --printappsettings command line argument:

myapp --printappsettings

This generates an appsettings.fig.json file in the current working directory containing all settings with their default values.

Providing Value Overrides

You can override default values by providing key=value pairs after the flag:

myapp --printappsettings MySetting=myvalue AnotherSetting="different value"

Overrides are matched case-insensitively to setting names.

Example

Given a settings class:

public class MySettings : SettingsBase
{
    [Setting("API URL")]
    public string ApiUrl { get; set; } = "https://example.com";

    [Setting("Max Retries")]
    public int MaxRetries { get; set; } = 3;

    [Setting("Password")]
    [Secret]
    public string Password { get; set; } = "";
}

Running:

myapp --printappsettings ApiUrl=https://api.mycompany.com MaxRetries=5 Password=MySecret

Produces an appsettings.fig.json file containing:

{
  "ApiUrl": "https://api.mycompany.com",
  "MaxRetries": "5",
  "Password_FigEncrypted": "<DPAPI encrypted value of MySecret>"
}

Secret Settings

Settings marked with the [Secret] attribute receive special handling:

• The plain setting name is not included in the file
• Instead, the setting appears as <SettingName>_FigEncrypted with a DPAPI-encrypted value
• The encrypted value is tied to the currently logged-in user on the machine where the command is run

Windows Only

DPAPI encryption is supported only on Windows. On Linux and macOS, secret settings are omitted from the generated file and a warning is printed to the console.

Using the Generated File Offline

Once you have an appsettings.fig.json, you can rename if to appsettings.json and run your application without a Fig server using the --figoffline argument. See the Running Offline Without a Fig Server guide for the complete workflow.

Passing Arguments to Fig

To use these command line arguments, pass them through FigOptions.CommandLineArgs in your application setup. If your application already uses a DpapiSecretProvider (from the Fig.Client.SecretProvider.Dpapi package), DPAPI encryption is enabled automatically — no extra configuration is required:

var configuration = new ConfigurationBuilder()
    .AddFig<MySettings>(o =>
    {
        o.ClientName = "My App";
        o.CommandLineArgs = args;  // Pass args from Program.cs
        o.ClientSecretProviders = [new DpapiSecretProvider()];  // Enables DPAPI for both client secrets and appsettings encryption
        // ... other options
    })
    .Build();

The DpapiSecretProvider class is in the Fig.Client.SecretProvider.Dpapi NuGet package and implements both IClientSecretProvider and IAppSettingsEncryptionProvider. If no provider that implements IAppSettingsEncryptionProvider is found in ClientSecretProviders, secret settings are omitted from the generated file and a warning is printed to the console.

Extensible encryption

The IAppSettingsEncryptionProvider interface (in Fig.Client.Contracts) allows alternative encryption providers. Any IClientSecretProvider that also implements IAppSettingsEncryptionProvider will be detected automatically — simply add it to FigOptions.ClientSecretProviders.