# How to Customize or Extend the Functionality of dotnet/skills: Complete Plugin Guide > Customize and extend dotnet/skills functionality by creating plugins, adding skills, or defining agents. Edit markdown files without compiling code. - Repository: [.NET Platform/skills](https://github.com/dotnet/skills) - Tags: how-to-guide - Published: 2026-07-08 --- **You can customize or extend dotnet/skills by creating new plugins, adding skills to existing plugins, or defining agents—all by editing markdown files without compiling code.** The dotnet/skills repository provides Microsoft's plugin-based architecture for AI coding assistants. When you need to customize or extend the functionality of dotnet/skills, you work within a directory structure of markdown files and JSON manifests that requires no code compilation, using the runtime discovery system implemented in [`eng/skill-validator/src/Program.cs`](https://github.com/dotnet/skills/blob/main/eng/skill-validator/src/Program.cs) to automatically index new capabilities. ## Understanding the Plugin Architecture The repository organizes functionality through a strict directory convention under the `plugins/` folder. Each subdirectory represents a self-contained plugin containing a **plugin manifest** ([`plugin.json`](https://github.com/dotnet/skills/blob/main/plugin.json)), optional **skills** in markdown format, and optional **agent specifications**. According to the source code in [`plugins/dotnet-test/plugin.json`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/plugin.json), the manifest declares the plugin's metadata, version, and pointers to skill directories. The runtime loads every plugin discovered in the repository, parsing front-matter from [`SKILL.md`](https://github.com/dotnet/skills/blob/main/SKILL.md) files to build a JSON schema that surfaces capabilities via the standard Agentskills protocol. ## Three Methods to Customize or Extend dotnet/skills ### Create a New Plugin To add entirely new functionality, create a new directory under `plugins/` with a [`plugin.json`](https://github.com/dotnet/skills/blob/main/plugin.json) manifest. For example, to create a logging plugin: ```json { "name": "dotnet-logging", "version": "0.1.0", "description": "Skills for configuring logging in .NET applications.", "skills": ["./skills/"], "agents": [] } ``` Place this in [`plugins/dotnet-logging/plugin.json`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-logging/plugin.json). The repository's CI pipeline automatically picks up this new plugin, publishes it to [`.agents/plugins/marketplace.json`](https://github.com/dotnet/skills/blob/main/.agents/plugins/marketplace.json), and makes it available for installation via `/plugin install dotnet-logging@dotnet-agent-skills`. ### Add a Skill to an Existing Plugin Skills reside in `plugins//skills//SKILL.md` as markdown files with YAML front-matter. To extend the `dotnet-test` plugin with xUnit support, create [`plugins/dotnet-test/skills/generate-xunit-tests/SKILL.md`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/skills/generate-xunit-tests/SKILL.md): ```markdown --- name: generate-xunit-tests description: Generate xUnit test scaffolding from production code. license: MIT --- # Generate xUnit Tests ## When to Use - User wants a fresh xUnit test project for a given source file. ## Inputs | Input | Required | Description | |-------|----------|-------------| | source-code | Yes | C# source file to test | | project-name | No | Desired test project name | ## Workflow 1. Parse public members in source-code. 2. Create test classes with [Fact] methods. 3. Emit project file referencing xunit packages. ``` The manifest at [`plugins/dotnet-test/plugin.json`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/plugin.json) already points to `"./skills/"`, so the CI pipeline automatically includes your new skill without requiring manifest updates. ### Define a New Agent Agents guide how coding assistants invoke skills. Add a new agent by creating a markdown file under `plugins//agents/.agent.md`. For the logging plugin example, you might create [`plugins/dotnet-logging/agents/configure-logging.agent.md`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-logging/agents/configure-logging.agent.md): ```markdown # Configure Logging Agent You are a .NET logging expert. When the user asks to set up logging: 1. Gather the desired provider (Serilog, NLog, built-in). 2. Ask for the target project file if not supplied. 3. Invoke the configure-logging skill with appropriate inputs. 4. Return modified .csproj and NuGet references. ``` Add the filename to the `agents` array in [`plugin.json`](https://github.com/dotnet/skills/blob/main/plugin.json), or omit the field to enable auto-discovery depending on your runtime version. ## Implementation Examples ### Example: Extending the MSTest Plugin The existing [`plugins/dotnet-test/skills/writing-mstest-tests/SKILL.md`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/skills/writing-mstest-tests/SKILL.md) demonstrates the full structure required, including inputs, workflow sections, and example outputs. When you customize this file or add parallel skills in the same directory, you follow the same front-matter pattern shown in the MSTest skill, which declares the skill name, description, and licensing information in the YAML header. ### Example: Plugin Manifest Structure The `dotnet-test` manifest in [`plugins/dotnet-test/plugin.json`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/plugin.json) illustrates the relationship between components: ```json { "name": "dotnet-test", "version": "1.0.0", "skills": ["./skills/"], "agents": ["./agents/"] } ``` This structure tells the validator in [`eng/skill-validator/src/Program.cs`](https://github.com/dotnet/skills/blob/main/eng/skill-validator/src/Program.cs) where to locate skill definitions and agent specifications during the CI evaluation pipeline. ## Critical Files in the Repository When you customize or extend dotnet/skills, these files determine how your changes integrate with the ecosystem: - **[`README.md`](https://github.com/dotnet/skills/blob/main/README.md)** (root) – Central hub listing all plugins and installation instructions for Copilot CLI, Claude Code, Cursor, and Codex clients. - **`plugins//plugin.json`** – Defines plugin identity, version, and directory mappings for skills and agents (see [`plugins/dotnet-test/plugin.json`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/plugin.json)). - **`plugins//skills/**/SKILL.md`** – Contains the actual skill specifications with front-matter, inputs, and workflow descriptions (reference [`plugins/dotnet-test/skills/writing-mstest-tests/SKILL.md`](https://github.com/dotnet/skills/blob/main/plugins/dotnet-test/skills/writing-mstest-tests/SKILL.md)). - **`plugins//agents/*.agent.md`** – Optional agent specifications that shape LLM invocation patterns. - **[`.agents/plugins/marketplace.json`](https://github.com/dotnet/skills/blob/main/.agents/plugins/marketplace.json)** – Auto-generated manifest that makes plugins discoverable by client applications. - **[`eng/skill-validator/src/Program.cs`](https://github.com/dotnet/skills/blob/main/eng/skill-validator/src/Program.cs)** – Runtime entry point used by CI to validate and index plugin manifests. ## Summary - **New Plugins**: Create a directory under `plugins/`, add [`plugin.json`](https://github.com/dotnet/skills/blob/main/plugin.json), and populate with skills or agents to extend dotnet/skills with entirely new capabilities. - **New Skills**: Add [`SKILL.md`](https://github.com/dotnet/skills/blob/main/SKILL.md) files under `plugins//skills/` to customize existing plugins with additional functionality. - **New Agents**: Add `*.agent.md` files under `plugins//agents/` to modify how AI assistants invoke your skills. - **No Compilation Required**: All customization happens through markdown and JSON files parsed by the CI pipeline and surfaced via the marketplace manifest. ## Frequently Asked Questions ### Do I need to compile C# code to customize dotnet/skills? No. According to the repository structure, you customize or extend functionality by editing markdown files and JSON manifests. The runtime parses these plain-text files directly, eliminating the need for code compilation. ### How does the runtime discover new plugins I create? The CI pipeline automatically discovers new plugins by scanning the `plugins/` directory. When you push changes, [`eng/skill-validator/src/Program.cs`](https://github.com/dotnet/skills/blob/main/eng/skill-validator/src/Program.cs) validates your [`plugin.json`](https://github.com/dotnet/skills/blob/main/plugin.json), indexes the skills, and updates [`.agents/plugins/marketplace.json`](https://github.com/dotnet/skills/blob/main/.agents/plugins/marketplace.json) to make your plugin available to clients like Copilot CLI and Claude Code. ### What is the difference between a skill and an agent in dotnet/skills? A **skill** (defined in [`SKILL.md`](https://github.com/dotnet/skills/blob/main/SKILL.md)) specifies what the AI can do, including inputs, workflows, and examples. An **agent** (defined in `*.agent.md`) specifies how the AI should invoke that skill, providing prompt templates and context management. Skills define capabilities; agents define invocation behavior. ### Can I modify existing skills without breaking the plugin? Yes. Since skills are markdown files, you can edit existing [`SKILL.md`](https://github.com/dotnet/skills/blob/main/SKILL.md) files under `plugins//skills/` to refine workflows or update examples. The CI pipeline validates changes against the schema, and updates are automatically published, allowing you to customize dotnet/skills iteratively.