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 they are authoring before publishing
• 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

Rules that change the answer

Use these structures exactly; do not invent fields from other template features.

Deliver the requested artifact. When the user says "show", "write", or "give me the content", put the complete JSON/XML in the final response even if you also wrote it to disk. Never edit this skill's SKILL.md or plugin documentation as a substitute for authoring the user's template. Only create or modify template files when the user requested file changes and the target template/project is present.

Need	Correct structure	Never use
Conditional XML in a .csproj	XML comments such as <!--#if (database == "SqlServer") --> and <!--#endif --> around the complete element	bare #if lines, which make the XML invalid
Restore generated projects	restore action 210D431B-A78B-4D2F-B762-4ED3E3EA9025; use primaryOutputs, or args.files containing source-template paths/globs	run-script fields such as executable on the restore action
Restrict to the SDK host	a host constraint whose args is an array containing { "hostname": "dotnetcli" }; its optional version restricts the host/CLI version	using host version when the requirement is specifically the active SDK version, the invalid host ID dotnet-cli, or unrelated pattern / value fields
Restrict the active SDK version	an sdk-version constraint with a NuGet version/range string in args	a machine-specific exact patch unless the template truly requires it
Preserve CPM	keep generated PackageReference items versionless and package the owning Directory.Packages.props when the template is self-contained	adding inline Version attributes
Package templates	a pack project with <PackageType>Template</PackageType> and template content packed below content/	describing a layout without showing the requested project file

Step 1: Bootstrap from existing project

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

1. Copy the source project into a dedicated template-source directory by default, preserving the original project untouched. Modify the original in place only when the user explicitly asks for that layout.
2. Create .template.config inside the template-source directory.
3. Generate template.json with identity (reverse-DNS), name, shortName, sourceName (project name for replacement), classifications, and tags
4. 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" }
}

Required output — do not stop at a minimal stub. Write the complete .template.config/template.json for the actual source project, then emit a short conventions-preserved confirmation so the user can see nothing was silently dropped. This carry-over is the whole value of the skill; a generic dotnet new template that loses these is why authoring ties with a hand-written stub.

Source .csproj setting	Carried over?	How
SDK (Microsoft.NET.Sdk.*)	✅	template content .csproj uses same SDK
TreatWarningsAsErrors / Nullable / LangVersion	✅	preserved verbatim in template .csproj
PackageReference PrivateAssets / IncludeAssets / ExcludeAssets	✅	metadata kept on each reference
CPM (Directory.Packages.props present)	✅	ManagePackageVersionsCentrally remains enabled and no inline Version attributes are emitted

Mark any row you intentionally omitted as ⚠️ with a reason — never leave it implicit.

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 the file type's valid syntax. In XML use template directives inside XML comments, not bare preprocessor lines:

   <!--#if (database == "SqlServer") -->
   <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" />
   <!--#endif -->
   <!--#if (database == "Postgres") -->
   <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" />
   <!--#endif -->
   

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

For a restore post-action, prefer primaryOutputs when the project path is known:

"primaryOutputs": [{ "path": "MyProject.csproj" }],
"postActions": [{
  "description": "Restore NuGet packages.",
  "manualInstructions": [{ "text": "Run 'dotnet restore'." }],
  "actionId": "210D431B-A78B-4D2F-B762-4ED3E3EA9025",
  "continueOnError": true
}]

If args.files is needed, its paths are matched against the source template before renames, for example "files": ["**/*.csproj"]. Explain that distinction.

Step 4: Test the template locally

For a create-from-existing-project request, this step is required rather than optional: install the authored template, run a dry-run, instantiate it into a temporary output folder, and build the generated project. Report each observed result; inspecting template.json alone does not prove the reusable template works.

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

When packaging is requested, include the complete pack project, not only a directory tree:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <PackageId>Contoso.ProjectTemplates</PackageId>
    <PackageType>Template</PackageType>
    <TargetFramework>net8.0</TargetFramework>
    <IncludeBuildOutput>false</IncludeBuildOutput>
    <NoWarn>$(NoWarn);NU5128</NoWarn>
  </PropertyGroup>
  <ItemGroup>
    <Compile Remove="**\*" />
    <Content Include="templates\**\*" Pack="true" PackagePath="content\" />
  </ItemGroup>
</Project>

The pack project's target framework applies only to the content-only packaging project; it does not retarget projects inside templates/. Prefer a broadly available supported framework unless the packaging project itself uses newer build features.

For a self-contained CPM template, the packaged Directory.Packages.props must include <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally> and every versionless PackageReference must have a matching PackageVersion. Keep the props file at the intended generated repository root; do not place a duplicate nearer the project where it changes lookup.

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
• XML template directives are wrapped in XML comments and the generated project parses
• Host constraints use args[].hostname; restore actions use primaryOutputs or args.files

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 that match a dotnet new subcommand; read the live set from dotnet new --help and don't hardcode it (illustrative examples: install, uninstall, update, list, search, details, create). Top-level verbs like build/run/test/publish are fine. Run 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.
Reusing fields from a different constraint or post-action	Follow the exact schema: host.args[].hostname, and restore args.files rather than run-script fields.

More Info

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