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Use a repo-root `.editorconfig` to configure free .NET analyzer and style rules. Use when a .NET repo needs rule severity, code-style options, section layout, or analyzer ownership made explicit. USE FOR: the repo needs a root .editorconfig; analyzer severity and style ownership are unclear; the team wants one source of truth for rule configuration. DO NOT USE FOR: choosing analyzers with no config change; formatting-only execution with no config ownership question. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Symbolicate .NET runtime frames in Apple platform .ips crash logs (iOS, tvOS, Mac Catalyst, macOS). Extracts UUIDs and addresses from the native backtrace, locates dSYM debug symbols, and runs atos to produce function names with source file and line numbers. Automatically downloads .dwarf symbols from the Microsoft symbol server using Mach-O UUIDs. USE FOR triaging a .NET MAUI or Mono app crash from an .ips file on any Apple platform, resolving native backtrace frames in libcoreclr or libmonosgen-2.0 to .NET runtime source code, retrieving .ips crash logs from a connected iOS device or iPhone, or investigating EXC_CRASH, EXC_BAD_ACCESS, SIGABRT, or SIGSEGV originating from the .NET runtime. DO NOT USE FOR pure Swift/Objective-C crashes with no .NET components, or Android tombstone files. INVOKES Symbolicate-Crash.ps1 script, atos, dwarfdump, idevicecrashreport.

Diagnoses .NET Framework CLR activation issues using CLR activation logs (CLRLoad logs) produced by mscoree.dll. Use when: the shim picks the wrong runtime, fails to load any runtime, shows unexpected .NET 3.5 Feature-on-Demand (FOD) dialogs, unexpectedly does NOT show FOD dialogs, loads both v2 and v4 into the same process causing failures, or any time someone is wondering "what is happening with .NET Framework activation?"

Use the free built-in .NET SDK analyzers and analysis levels with gradual Roslyn warning promotion. USE FOR: the repo wants first-party .NET analyzers; CI should fail on analyzer warnings; the team needs AnalysisLevel or AnalysisMode guidance. DO NOT USE FOR: third-party analyzer selection by itself; formatting-only work. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Provides file paths to language-specific extension files for the code-testing pipeline. Call this skill to discover available extension guidance files (e.g., dotnet.md for .NET, cpp.md for C++). Do not use directly — invoked by code-testing agents and skills that need language-specific references.

Use the open-source CodeQL ecosystem for .NET security analysis. Use when a repo needs CodeQL query packs, CLI-based analysis on open source codebases, or GitHub Action setup with explicit licensing caveats. USE FOR: the repo uses or wants CodeQL for .NET security analysis; GitHub code scanning is part of the CI plan. DO NOT USE FOR: teams that need a tool with no private-repo licensing caveat. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Use free built-in .NET maintainability analyzers and code metrics configuration to find overly complex methods and coupled code. USE FOR: the team wants to find overly complex methods; cyclomatic complexity thresholds are needed in CI; maintainability metrics or coupling thresholds need to be configured. DO NOT USE FOR: formatting-only work; generic analyzer setup with no complexity policy change. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Use the open-source free `CSharpier` formatter for C# and XML. Use when a .NET repo intentionally wants one opinionated formatter instead of a highly configurable `dotnet format`-driven style model. USE FOR: the repo uses or wants CSharpier; the team prefers an opinionated formatter over many configurable style knobs. DO NOT USE FOR: repos that already standardized on dotnet format as the only formatter. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Scan C# source files for hard-to-test static dependencies — DateTime.Now/UtcNow, File.*, Directory.*, Environment.*, HttpClient, Console.*, Process.*, and other untestable statics. Produces a ranked report of static call sites by frequency. USE FOR: find untestable statics, scan for static dependencies, testability audit, identify hard-to-mock code, find DateTime.Now usage, detect static coupling, testability report, static analysis for testability. DO NOT USE FOR: generating wrappers (use generate-testability-wrappers), migrating code (use migrate-static-to-wrapper), general code review, or finding statics that are already behind abstractions.

Configure and collect crash dumps for modern .NET applications. USE FOR: enabling automatic crash dumps for CoreCLR or NativeAOT, capturing dumps from running .NET processes, setting up dump collection in Docker or Kubernetes, using dotnet-dump collect or createdump. DO NOT USE FOR: analyzing or debugging dumps, post-mortem investigation with lldb/windbg/dotnet-dump analyze, profiling or tracing, or for .NET Framework processes.

Use ESLint in .NET repositories that ship JavaScript, TypeScript, React, or other Node-based frontend assets. USE FOR: the repo has package.json, eslint.config.*, .eslintrc*, tsconfig.json, or JS/TS/React frontend files; the user asks for JavaScript or TypeScript linting, React rule. DO NOT USE FOR: CSS ownership by itself; route that to stylelint; HTML-only checks on static output; route that to htmlhint. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Add or update automated tests for a change using the repository’s verification rules in `AGENTS.md`. Use when implementing a feature, bugfix, refactor, or regression test; prefer stable integration/API/UI coverage and pull deeper test strategy from the bundled references.

Mechanically replace static dependency call sites with wrapper or built-in abstraction calls across a bounded scope (file, project, or namespace). Performs codemod-style bulk replacement of DateTime.UtcNow to TimeProvider.GetUtcNow(), File.ReadAllText to IFileSystem, and similar transformations. Adds constructor injection parameters and updates DI registration. USE FOR: replace DateTime.Now/UtcNow with TimeProvider, migrate static calls to wrapper, bulk replace File.* with IFileSystem, codemod static to injectable, add constructor injection for a dependency, mechanical or scoped migration of statics, convert static calls to use an abstraction, update call sites. DO NOT USE FOR: detecting statics (use detect-static-dependencies), generating wrappers (use generate-testability-wrappers), migrating between test frameworks.

Write, run, or repair .NET tests that use MSTest. Use when a repo uses `MSTest.Sdk`, `MSTest`, `[TestClass]`, `[TestMethod]`, `DataRow`, or Microsoft.Testing.Platform-based MSTest execution. USE FOR: the repo uses MSTest; you need to add, run, debug, or repair MSTest tests; the repo is moving between VSTest and Microsoft.Testing.Platform. DO NOT USE FOR: xUnit projects; TUnit projects. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Use the open-source free `Stryker.NET` mutation testing tool for .NET. Use when a repo needs to measure whether tests actually catch faults, especially in critical libraries or domains. USE FOR: the repo uses or wants Stryker.NET; mutation testing is needed for high-risk code. DO NOT USE FOR: every PR path by default in a large repo; simple coverage collection. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Provides file paths to language-specific reference files for the test ANALYSIS skills (assertion-quality, test-anti-patterns, test-gap-analysis, test-smell-detection, test-tagging). Call this skill to discover available extension files (e.g., dotnet.md for .NET/MSTest/xUnit/NUnit/TUnit, python.md for pytest/unittest, typescript.md for Jest/Vitest/Mocha, java.md for JUnit/TestNG, etc.). Do not use directly — invoked by the test-quality-auditor agent and polyglot analysis skills that need framework-specific lookup tables (test markers, assertion APIs, skip annotations, sleep patterns, mystery guest indicators, integration markers, setup/teardown, tag-support capability).

Write, create, modernize, or fix comprehensive MSTest unit tests with MSTest 3.x/4.x APIs. USE FOR: write or create MSTest unit tests, fix/modernize MSTest assertions, better MSTest assertion than Assert.IsTrue, replace hard cast with type check (IsInstanceOfType), MSTest assertion APIs (Contains, ContainsSingle, HasCount, IsEmpty, IsNotEmpty, DoesNotContain, AreSame, IsNull, StartsWith, EndsWith, MatchesRegex, IsGreaterThan, IsLessThan, IsInRange), swapped Assert.AreEqual args, replace ExpectedException with Assert.Throws, data-driven (DataRow, DynamicData, ValueTuples), lifecycle (TestInitialize, TestCleanup, TestContext), async tests and cancellation tokens, conditional execution/retry/cleanup (OSCondition, Retry), parallelization (Parallelize/DoNotParallelize), MSTest.Sdk setup, MSTESTxxxx analyzer fixes. DO NOT USE FOR: test quality audits (use test-anti-patterns), running tests (use run-tests), MSTest version migration (use the migrate-mstest skills), xUnit/NUnit/TUnit, or non-.NET languages.

Analyzes the variety and depth of assertions across test suites in any language. Use when the user asks to evaluate assertion quality, find shallow tests, identify assertion-free tests (no assertions or only trivial ones like Assert.IsNotNull / toBeTruthy()), flag self-referential or tautological assertions, measure assertion diversity, or audit whether tests verify different facets of behavior. Polyglot: .NET, Python, TS/JS, Java, Go, Ruby, Rust, Swift, Kotlin, PowerShell, C++. DO NOT USE FOR: writing new tests (use code-testing-agent / writing-mstest-tests), mutation reasoning about whether tests would catch a bug (use test-gap-analysis), or a general severity-ranked anti-pattern audit (use test-anti-patterns), fixing or rewriting assertions, or writing, fixing, or modernizing MSTest tests, assertions, or attributes (use writing-mstest-tests).

Use Biome in .NET repositories that ship Node-based frontend assets and want a fast combined formatter-linter-import organizer for JavaScript, TypeScript, CSS, JSON, GraphQL, or HTML. USE FOR: biome.json or @biomejs/biome setup; fast frontend formatting and linting; replacing overlapping frontend style tools deliberately. DO NOT USE FOR: ESLint-only plugin coverage; runtime site audits such as headers, accessibility, or browser behavior. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Generates and writes new unit tests for any programming language — scaffolds test projects and configures coverage tooling (coverlet, pytest-cov, @vitest/coverage-v8) as part of test generation. Use when asked to generate tests, generate pytest tests, generate Vitest tests, write unit tests, add tests, improve coverage, comprehensive tests, or scaffold a new test project or suite for an app, service, library, REST API, blueprint, or package — including project-wide, multi-file test generation across services, repositories, routes, and modules. Supports C#/.NET, Python (pytest, Flask/Django), TypeScript/JavaScript (Vitest, Jest, Mocha), Go, Rust, Java (JUnit). Runs a research, planning, and implementation pipeline so tests compile and pass. DO NOT USE FOR: running existing tests (use run-tests); analyzing existing coverage reports (use coverage-analysis or crap-score); writing, fixing, or modernizing MSTest-specific tests, assertions, attributes, or lifecycle (use writing-mstest-tests).

Project-wide code coverage and CRAP (Change Risk Anti-Patterns) score analysis for .NET projects. Calculates CRAP scores per method and surfaces risk hotspots — complex code with low coverage that is dangerous to modify. Use to diagnose why coverage is stuck or plateaued, identify what methods block improvement, or get project-wide coverage analysis with risk ranking. USE FOR: coverage stuck, coverage plateau, can't increase coverage, what's blocking coverage, coverage gap, CRAP scores, risk hotspots, where to add tests, coverage analysis, coverage report. DO NOT USE FOR: targeted single-method CRAP analysis (use crap-score); auditing test code for coverage-touching or other anti-patterns (use test-anti-patterns); writing tests; running tests (use run-tests). Requires or produces coverage (Cobertura) and CRAP metrics.

Generate wrapper interfaces and DI registration for hard-to-test static dependencies in C#. Produces IFileSystem, IEnvironmentProvider, IConsole, IProcessRunner wrappers, or guides adoption of TimeProvider and IHttpClientFactory. USE FOR: generate wrapper for static, create IFileSystem wrapper, wrap DateTime.Now, make static testable, make class testable, create abstraction for File.*, generate DI registration, TimeProvider adoption, IHttpClientFactory setup, testability wrapper, mock-friendly interface, mock time in tests, create the right abstraction to mock, how to mock DateTime, test code using File.ReadAllText, what abstraction for Environment, how to make statics injectable, adopt System.IO.Abstractions, make file calls testable. DO NOT USE FOR: detecting statics (use detect-static-dependencies), migrating call sites (use migrate-static-to-wrapper), general interface design not about testability.

Create or update an ADR under `docs/ADR/` for architectural decisions, dependency changes, data-model changes, or cross-cutting policy shifts. Use when the user asks to write, update, or document an ADR, record a design decision, capture architecture trade-offs, or justify a repo-wide technical policy.

Shape delivery workflow around backlog quality, roles, ceremonies, and engineering feedback. Use when defining how the team plans, tracks work, and turns feedback into durable improvements.

Create or update `docs/Architecture.md` as the global architecture map for a solution. Use when bootstrapping a repo, onboarding, or changing modules, boundaries, or contracts. Keep it navigational and use `references/overview-template.md` for scaffolding.

Prepare for, perform, or tighten code review workflow: PR scope, review checklist, reviewer expectations, and merge hygiene. Use when shaping pull requests, defining review policy, or auditing whether a change is review-ready.

Improve developer experience for multi-component solutions: onboarding, F5 contract, cross-platform tasks, local inner loop, and reproducible setup. Use when the repo is hard to run, debug, test, or onboard into.

Create or update a feature spec under `docs/Features/` with business rules, user flows, system behaviour, verification, and Definition of Done. Use when the user asks for a feature spec, executable requirements, acceptance criteria, behaviour documentation, or a pre-implementation plan for non-trivial behaviour changes.

Plan a human review for a large AI-generated code drop by reading the target area, tracing the natural user and system flows, identifying the riskiest boundaries, and prioritizing the files a human should inspect first. Use when the codebase is too large to review line-by-line and you need a practical review sequence plus a prioritized file list.

Apply ML/AI project delivery guidance for data exploration, feasibility, experimentation, testing, responsible AI, and operating ML systems. Use when the repo includes model training, inference, data science workflows, or ML-specific delivery planning.

Capture or refine non-functional requirements such as accessibility, reliability, scalability, maintainability, performance, and compliance. Use when a feature or architecture change needs explicit quality attributes and trade-offs.

Design or improve observability for application and delivery flows: logs, metrics, traces, correlation, alerts, and operational diagnostics. Use when a change affects runtime visibility, failure diagnosis, SLOs, or alerting.

Apply baseline engineering security guidance: secrets handling, secure defaults, threat modelling references, and review checkpoints for auth, data flow, pipelines, and external integrations. Use when a change has security impact but does not require a full standalone AppSec engagement.

Apply SOLID, SRP, cohesion, composition-over-inheritance, and small-file discipline to code changes. Use when refactoring large files or classes, setting maintainability limits in `AGENTS.md`, documenting justified exceptions, or reviewing design quality.

Set or refine source-control policy for repository structure, branch naming, merge strategy, commit hygiene, and secrets-in-git discipline. Use when bootstrapping a repo, tightening PR flow, or documenting branch and release policy.

Use UI/UX engineering guidance for design systems, accessibility, front-end technology selection, and design-to-development collaboration. Use when bootstrapping a UI project, choosing front-end stack, or tightening design and accessibility practices.

Add, repair, or review Playwright visual regression tests for browser-facing .NET apps, including screenshot baselines, Pixelmatch thresholds, deterministic rendering, and GitHub Actions artifacts. USE FOR: toHaveScreenshot, page.screenshot visual checks, Pixelmatch/pngjs comparison scripts, visual baseline updates, screenshot diff triage, or CI workflows for UI regression screenshots. DO NOT USE FOR: pure unit tests, accessibility audits, browser-debugging sessions, or frontend linting.

Run, filter, or troubleshoot .NET tests with `dotnet test`. USE FOR: running all tests in a project or solution; running only a subset (a specific test class, category, or trait) via filters; running a single target framework in a multi-TFM project (`--framework`); producing TRX reports; collecting crash or hang dumps; diagnosing why `dotnet test` fails or uses the wrong argument syntax. Detects the test platform (VSTest vs Microsoft.Testing.Platform) and framework (MSTest/xUnit/NUnit/TUnit), then picks the matching command: the `--` separator on .NET SDK 8/9 vs 10+, the right filter flag (--filter, --filter-class, --filter-trait, --filter-query, --treenode-filter), and TRX/blame flags. DO NOT USE FOR: writing test code (use code-testing-agent), iterating on failing tests without rebuilding (use mtp-hot-reload), CI/CD config, or debugging test logic.

Use SonarJS-derived rules in .NET repositories that ship JavaScript or TypeScript frontends and need deeper bug-risk, code-smell, or cognitive-complexity checks than a minimal ESLint baseline. USE FOR: SonarQube, SonarCloud, or eslint-plugin-sonarjs setups; frontend code smells; cognitive complexity and deeper bug-risk rules. DO NOT USE FOR: lightweight base lint setups with no extra smell or complexity rules; teams that reject Sonar tooling. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Use Stylelint in .NET repositories that ship CSS, SCSS, or other stylesheet assets alongside web frontends. USE FOR: stylelint.config.*, .stylelintrc*, CSS or SCSS assets; CSS linting; duplicate style cleanup and naming-convention checks. DO NOT USE FOR: JavaScript or TypeScript lint ownership; runtime accessibility, performance, SEO, or header checks. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.