.NET Tag Helper Expert Skill

Trigger On

• The user requests to create, generate, or design a custom Razor Tag Helper in C#.
• The user wants to encapsulate complex HTML/UI logic into reusable custom tags without using Partial Views or CSHTML.
• The target framework is .NET 6.0 (LTS) and above.

Workflow (Generator Pattern)

Follow these steps exactly to create robust, high-performance C# Tag Helpers.

Step 1: Perceive & Gather Requirements (Inversion)

Before writing any code, ask the user to clarify the following if not already provided:

1. Target HTML Tag: What is the name of the custom tag in HTML? (e.g., <my-button>, <user-card>)
2. Properties: What parameters/attributes should this tag accept? (e.g., theme, is-active, user-id)
3. Dependencies (DI): Does this tag need to query a database or call a service? (Needs Dependency Injection)
4. Context: Does it need to access ViewContext (e.g., to generate URLs or check model state)?

Step 2: Reason & Design (Planning)

Based on the answers:

• Class Naming: Ensure the class name ends with TagHelper (e.g., MyButtonTagHelper).
• Target Element: Apply [HtmlTargetElement("my-button")].
• Properties: Map HTML kebab-case attributes to C# PascalCase properties. Apply [HtmlAttributeName("is-active")] if necessary.
• Method Selection:
• If no IO/Async operations, override Process.
• If using DI for database/API calls, override ProcessAsync.

Step 3: Act (Code Generation)

Generate the complete C# class. Strictly adhere to the following rules:

1. Inherit from Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.
2. Do NOT generate .cshtml files. All HTML must be constructed using TagBuilder inside the C# class.
3. If ViewContext is needed, use [ViewContext] and [HtmlAttributeNotBound].
4. Manage content properly using output.TagName, output.Attributes.SetAttribute, and output.Content.SetHtmlContent.
5. Ensure Thread-Safety (do not store request-specific state in instance fields unless injected as scoped/transient).

Step 4: Validate (Quality Check)

Review the generated code against these criteria before presenting it:

• Are all properties strongly typed?
• Is TagBuilder used instead of string concatenation for HTML elements?
• Is ProcessAsync used correctly if awaiting tasks?

Deliverable

Present the C# code wrapped in a markdown code block. Briefly explain how to register it in _ViewImports.cshtml (e.g., @addTagHelper *, YourAssemblyName).

Documentation

Official References

• Tag Helpers in ASP.NET Core
• Authoring Tag Helpers

Internal References

• Tag Helper Coding Style & Advanced Patterns
• Tag Helper Coding Conventions
• Tag Helper Anti-Patterns