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

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 — generic dotnet new templates frequently get these wrong, so verify each is carried over from the original .csproj: 1. SDK type — Microsoft.NET.Sdk, Microsoft.NET.Sdk.Web, Microsoft.NET.Sdk.Worker, etc. 2. Analyzer/package reference metadata — PrivateAssets, IncludeAssets, ExcludeAssets 3. `OutputType` and other key properties — TreatWarningsAsErrors, Nullable, LangVersion 4. CPM participation — no inline Version attributes when a Directory.Packages.props is present 5. Custom build props/targets and Directory.Build.props conventions 6. Repo conventions — folder layout, naming, global.json SDK pin

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

Validate the generated template.json using the template-validation skill (it owns the full rule set — required fields, identity format, reserved shortName conflicts, parameter datatypes, post-actions, constraints, and tags).

Quick summary of what gets checked:

• Required fields — identity, name, and shortName must be present.
• ShortName conflicts — avoid names that collide with dotnet new subcommands. Read the authoritative set from the Commands: section of dotnet new --help for the installed SDK and do not hardcode it (it can change between versions); illustrative examples from current SDKs are install, uninstall, update, list, search, details, create. A conflict happens because dotnet new <name> would be parsed as the subcommand of the same name. Top-level dotnet verbs like build, run, test, and publish do NOT conflict. Run dotnet new list to confirm the name is not already taken.
• Parameters, post-actions, tags — see template-validation for the complete rules, including the valid datatype list.

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

More Info

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