template-authoring

Template Authoring

This skill helps an agent create and validate custom dotnet new templates. It guides bootstrapping templates from existing projects and validates template.json files for authoring issues before publishing.

When to Use

• User wants to create a reusable template from an existing .csproj
• User wants to validate a template.json for correctness
• User is setting up .template.config/template.json from scratch
• User wants to package a template for NuGet distribution

When Not to Use

• User wants to find or use existing templates — route to template-discovery or template-instantiation
• User has MSBuild issues unrelated to template authoring — route to dotnet-msbuild plugin

Inputs

Input	Required	Description
Source project path	For creation	Path to the .csproj to use as template source
template.json path	For validation	Path to an existing template.json to validate
Template name	For creation	Human-readable name for the template
Short name	Recommended	Short name for dotnet new <shortname> usage

Workflow

Step 1: Bootstrap from existing project

Analyze the source .csproj and create a .template.config/template.json:

1. Create .template.config directory next to the project
2. Generate template.json with identity (reverse-DNS), name, shortName, sourceName (project name for replacement), classifications, and tags
3. Preserve from source: SDK type, package references with metadata (PrivateAssets, IncludeAssets), properties (OutputType, TreatWarningsAsErrors), CPM patterns

Minimal example:

{
  "$schema": "http://json.schemastore.org/template",
  "author": "MyOrg",
  "classifications": ["Library"],
  "identity": "MyOrg.Templates.MyLib",
  "name": "My Library Template",
  "shortName": "mylib",
  "sourceName": "MyLib",
  "tags": { "language": "C#", "type": "project" }
}

Step 2: Validate template.json

Read and review the template.json for common authoring issues:

Validation checks to perform:

• Required fields — verify identity, name, and shortName are present
• Identity format — use reverse-DNS format (e.g., MyOrg.Templates.WebApi)
• Parameter issues — check datatypes are valid (string, bool, choice, int, float), choices have defaults, descriptions are present
• ShortName conflicts — avoid names that collide with built-in CLI commands (build, run, test, publish). Check with dotnet new list to see if the name is already taken
• Post-action completeness — verify post-actions have all required configuration
• Tags — ensure language, type, and classification tags are set for discoverability

Step 3: Refine the template

Based on validation results and user requirements:

1. Add parameters with appropriate types (string, bool, choice), defaults, and descriptions
2. Add conditional content using #if preprocessor directives for optional features
3. Configure post-actions for solution add, restore, or custom scripts
4. Set constraints to restrict which SDKs or workloads the template supports
5. Add classifications and tags for discoverability

Step 4: Test the template locally

dotnet new install ./path/to/template/root
dotnet new mylib --name TestProject --dry-run
dotnet new mylib --name TestProject --output ./test-output
dotnet build ./test-output/TestProject

Validation

• template.json passes manual validation with zero errors
• Template identity and shortName are unique and meaningful
• All parameters have descriptions and appropriate defaults
• Template can be installed, dry-run, and instantiated successfully
• Created projects build cleanly with dotnet build
• Conditional content produces correct output for all parameter combinations

Common Pitfalls

Pitfall	Solution
Identity format issues	Use reverse-DNS format (e.g., MyOrg.Templates.WebApi). Avoid spaces or special characters.
ShortName conflicts with CLI commands	Avoid names like build, run, test, publish. Check by running dotnet new list to see if the name is already taken.
Missing parameter descriptions	Every parameter should have a description and displayName for discoverability.
Not testing all parameter combinations	Use dotnet new <template> --dry-run with different parameter values to verify conditional content works correctly.
Hardcoded versions in template	Use sourceName replacement for project names and consider parameterizing framework versions.
Not setting classifications	Add appropriate classifications (e.g., ["Web", "API"]) for template discovery.

More Info

• Custom templates for dotnet new — official authoring guide
• template.json reference — full schema reference
• Template Engine Wiki — template engine internals