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:

Create .template.config directory next to the project
Generate template.json with identity (reverse-DNS), name, shortName, sourceName (project name for replacement), classifications, and tags
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:

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

template-authoring