2.2. Official plugins

Official plugins are first-party packages maintained alongside the core library. Each one ships as a separate NuGet package and adds one placeholder source. Install the ones you need and register them through the AddPlugins callback.

Package	Plugin	Tag	Kind	Input
StringTemplates.Configuration	ConfigurationTemplatePlugin	Configuration	Tag-only	–
StringTemplates.MailKit	MimeMessageTemplatePlugin	MimeMessage	Input-driven	MimeMessage

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StringTemplates.Configuration

Resolves values from the application's IConfiguration (appsettings, environment variables, secrets, etc.).

1. Installation

dotnet add package StringTemplates.Configuration

For more information, visit nuget.org/StringTemplates.Configuration.

2. Registration

ConfigurationTemplatePlugin is a tag-only plugin whose constructor takes an IConfiguration (supplied automatically by the DI container):

using StringTemplates;
using StringTemplates.Plugins;

builder.Services.AddStringTemplates(options => options.AddPlugins(opts => opts
    .AddPluginSingleton<ConfigurationTemplatePlugin>()));

3. Usage

Keys map onto configuration sections. A dot (.) in a placeholder key is translated into the configuration separator (:), so ConnectionStrings.Database reads ConnectionStrings:Database.

var result = templateService.ReplacePlaceholders(
    "DB: {{#Configuration#ConnectionStrings.Database#Configuration#}}");

Other examples:

• {{#Configuration#ConnectionStrings.Database#Configuration#}}
• {{#Configuration#KeyVault.Auth.ClientId#Configuration#}}

A key that does not exist in configuration is left untouched.

⚠️ Security note

This plugin can read any configuration value, including environment variables. It is intended for internal use only.

Do not expose it to untrusted input or end users, as it could be used to leak secrets and environment variables.

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StringTemplates.MailKit

Resolves values from a MailKit / MimeKit MimeMessage — its subject, recipients, sender, etc. It is an input-driven plugin, so you pass the MimeMessage to ReplacePlaceholders.

1. Installation

dotnet add package StringTemplates.MailKit

For more information, visit nuget.org/StringTemplates.MailKit.

2. Registration

using MimeKit;
using StringTemplates;
using StringTemplates.Plugins;

builder.Services.AddStringTemplates(options => options.AddPlugins(opts => opts
    .AddPluginSingleton<MimeMessageTemplatePlugin, MimeMessage>()));

3. Usage

var message = new MimeMessage();
message.Subject = "Welcome";
message.From.Add(new MailboxAddress("Stratis", "stratis@example.com"));
message.To.Add(new MailboxAddress("Alice", "alice@example.com"));

var result = templateService.ReplacePlaceholders(
    "Hi {{#MimeMessage#To.First.Name#MimeMessage#}}, "
    + "your message \"{{#MimeMessage#Subject#MimeMessage#}}\" "
    + "was sent from {{#MimeMessage#From.First.UserName#MimeMessage#}}.",
    message);

Result:

Hi Alice, your message "Welcome" was sent from stratis.

Supported keys

The same set of keys is available for the From, To, Cc and Bcc address lists. Replace <List> with one of From / To / Cc / Bcc:

Placeholder	Resolves to
{{#MimeMessage#<List>#MimeMessage#}}	All addresses, comma-joined (e.g. "Alice" <alice@example.com>, ...)
{{#MimeMessage#<List>.Count#MimeMessage#}}	Number of addresses
{{#MimeMessage#<List>.First#MimeMessage#}}	First full address
{{#MimeMessage#<List>.First.Name#MimeMessage#}}	First address' display name
{{#MimeMessage#<List>.First.UserName#MimeMessage#}}	First address' local part (before @)
{{#MimeMessage#<List>.Last#MimeMessage#}}	Last full address
{{#MimeMessage#<List>.Last.Name#MimeMessage#}}	Last address' display name
{{#MimeMessage#<List>.Last.UserName#MimeMessage#}}	Last address' local part (before @)
{{#MimeMessage#<List>.Names#MimeMessage#}}	All display names, comma-joined

Plus the subject:

Placeholder	Resolves to
{{#MimeMessage#Subject#MimeMessage#}}	The message subject
{{#MimeMessage#Subject.Length#MimeMessage#}}	The subject's length

Notes

• An empty address list yields an empty string (and Count yields 0).
• An unknown key, e.g. {{#MimeMessage#Does.Not.Exist#MimeMessage#}}, is left untouched.

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References:

• Default plugins
• Custom plugins
• PluginOptions