unity-coding-skills

A Claude Code plugin for Unity development that enables coding agents to work autonomously through a test-first workflow — writing reliable, maintainable tests before production code, then iterating to completion without constant oversight.

Reliable tests give the agent a clear signal: green means done. This plugin provides the methodology, conventions, and tools to make that signal trustworthy.

Tip

This plugin relies on Claude Code-specific features, such as the bundled /simplify skill and frontmatter fields of skills and subagents. If you use the skills with a different coding agent, please modify them accordingly.

Skills

Skill	Description	Required	User-invocable
code-writing-guide	Coding conventions and guidelines for Unity C# projects
edit-scene	Creates and modifies .unity and .prefab files	Rider built-in MCP Server and Extension for Unity plugin	✅
fix-bug	Diagnoses and fixes bugs using a test-first workflow (reproduce, diagnose, fix)		✅
plan-feature	Orchestrates the test-first planning workflow for feature implementation in plan mode		✅
refine-tests	Reviews existing test code for conformance to the test design and writing guides, then applies the refinements		✅
resolve-diagnostics	Resolves IDE diagnostics at warning or higher severity in the specified files, then reformats them	Rider built-in MCP Server	✅
run-tests	Running Unity tests via the run_unity_tests tool	Rider built-in MCP Server and Extension for Unity plugin	✅
test-designing-guide	Design maintainable test cases; reduce redundant tests, tests without assertions, and unnecessary test doubles
test-writing-guide	Conventions for writing Unity Test Framework test code	Test Helper and UI Test Helper package
unity-yaml-editing-guide	Guidelines for directly hand-editing Unity YAML asset files

Tip

Some skills require the JetBrains Rider built-in MCP server, IDE plugins, or UPM packages listed in the "Required" column above. If you don't use Rider or these packages, please modify the skill accordingly.

Tip

The Rider built-in MCP server also provides tools useful for coding agents, such as list_directory_tree, search_file, search_regex, search_symbol, and search_text.

Subagents

Agent	Description
failing-test-writer	Implements test code from the plan file's Test Cases table and confirms tests fail as expected (Step 2 of dev workflow)
test-deduplicator	Removes duplicate tests and merges parameterizable tests in modified test files (Step 4 of dev workflow)
test-designer	Designs test cases during plan mode after class/method designs are produced, using the test-designing-guide skill

Usage

Test-first feature implementation planning

/plan-feature <SPEC>

The created plan file includes the following:

• Layered-designed test cases to reduce redundant tests, tests without assertions, and unnecessary test doubles:
  • Editor tests (Edit Mode tests for editor extensions and validate assets)
  • Unit tests (Play Mode tests for runtime code)
  • Integration tests including UI operation and layout assertions
  • Visual verification tests using image analysis
• Test-first development workflow
  • Effective (failable) test code
  • Definition of Done
  • Safe refactoring to improve internal quality (uses /simplify skill and static analysis)

Important

This skill requires plan mode.

Bug fixes through reproduction testing

/fix-bug <INCIDENT>

Create, run, and verify tests to reproduce the bug, then fix it.

Important

This skill must be used outside plan mode.

Tip

The INCIDENT can specify an issue description or the failed test name.

Note

Depending on the incident, the root cause may be identified before writing a reproduction test. Under adjustment.

Refine existing test code for conformance to the test design and writing guides

/refine-tests <PATH>

Note

This skill is intended for use outside plan mode, but it can also be used from plan mode.

Installation

User-scope installation

Add the marketplace and install the plugin:

/plugin marketplace add nowsprinting/unity-coding-skills
/plugin install unity-coding-skills@nowsprinting-unity-coding-skills

Project-scope installation (team sharing)

Add the marketplace and install the plugin with --scope project:

/plugin marketplace add nowsprinting/unity-coding-skills
/plugin install unity-coding-skills@nowsprinting-unity-coding-skills --scope project

Commit the resulting .claude/settings.json to your repository.

Note

When team members trust the project folder, Claude Code prompts them to install the marketplace and plugin automatically.

Recommended Rider and Unity Project Settings

1. MCP server configuration

Some skills require the JetBrains Rider built-in MCP Server and extension plugin.

1. Open Settings > Tools > MCP Server
2. Turn on Enable MCP Server
3. Click the Auto-Configure button for the coding agent you use (e.g., Claude Code)
4. Install the MCP Server Extension for Unity plugin

Important

JetBrains Rider 2026.2.1 or later is recommended.

Important

On Rider 2026.2, when both the JetBrains and Rider MCP toolsets are enabled, they expose tools with the same name. Prefer the tools provided by Rider, and disable the duplicates:

• Under the Analysis toolset: get_file_problems, lint_files
• Under the Formatting toolset: reformat_file

Note

The MCP server is registered under different names depending on your Rider version: rider on Rider 2026.2 or later, jetbrains on versions earlier than 2026.2.

Note

When Rider is earlier than 2026.2 and you are using other JetBrains IDEs simultaneously with Rider, port numbers are assigned in the order they are launched. For example, if you launch Rider after IDEA, the port number for Rider will be 64343.

Note

Once configured in Rider, the Rider built-in MCP Server and extension plugin work in other Unity projects without additional setup.

2. Install UTF Analyzers (strongly recommended)

UTF Analyzers diagnose Unity Test Framework API usages that freeze the Unity Editor (e.g., Assert.ThrowsAsync, async delegates in Throws constraints, DelayedConstraint) before tests run. Install either the UPM package via OpenUPM or the NuGet package via NuGetForUnity.

Tip

If you install the UPM package, you do not need to add a reference to the test assembly definition file (asmdef). It also installs the following:

• Unity Test Framework v1.4.6 (dependency)
• NUnit.Analyzers v3.9.0 (bundled)

3. Enforcing coding rules via analyzers and inspections

Some skills resolve Roslyn analyzer and IDE inspection diagnostics at warning or higher severity during the refactoring phase. Therefore, any coding rule you want coding agents to respect must be set to warning or higher severity in .editorconfig or .globalconfig.

Tip

To add coding rules not covered by IDE inspections, you can install open-source Roslyn analyzers. Unity can load only analyzers built against the Roslyn version it supports, so check Which version of Roslyn analyzers should I use with Unity? for the version compatible with your project's Unity version.

Code written by coding agents often has maintainability problems, such as leftover unused members and overly complex methods. The following settings examples help coding agents avoid them.

Example: Unused types and members

To prevent leaving unused types and members, add the following to .editorconfig:

resharper_unused_type_local_highlighting = warning
resharper_unused_type_global_highlighting = warning
resharper_unused_member_global_highlighting = warning
resharper_unused_member_local_highlighting = warning

Example: Method complexity

To keep method complexity under control, install one of the following Rider plugins:

• CognitiveComplexity plugin
• CyclomaticComplexity plugin

Warning

In Rider 2026.2.1, there is an issue where the get_file_problems and lint_files tools fail to correctly return diagnostic messages from plugins. see: RIDER-142275

4. Untracking temporary files via .gitignore

Some skills place temporary editor script files under Assets/UnityCodingSkills/. Adding the following pattern to your project's .gitignore is recommended:

Assets/UnityCodingSkills*

Contributing

Contributions are welcome. However, we will decline contributions that we cannot maintain — such as adding support for different coding agents or MCP servers. Please fork this repository and customize it for your needs instead.

License

This project is released into the public domain under the Unlicense.