dotnet

Core .NET and C# skills for coding agents.

Includes

• Common .NET development skills
• A C# language server integration for .cs files

LSP

This plugin declares a C# LSP server that is launched through the .NET CLI. The LSP declaration is available to hosts that support the plugin lspServers extension. Codex plugin installs expose this plugin's skills but do not load that host-specific LSP declaration.

Prerequisites:

• .NET 10 SDK installed
• dotnet available on PATH

Skills

• csharp-expert
• csharp-refactoring
• msbuild — routed MSBuild diagnosis, performance, and authoring guidance
• setup-local-sdk

MSBuild entry and specialist skills

msbuild is the task-routed entry for build failures, build performance, and MSBuild authoring review. It loads bundled references rather than activating the specialist skills in the dotnet-msbuild plugin. The existing plugin's skills and agents remain supported, unchanged alternative entry points; installing both plugins does not require running both workflows for one task.

Authoring review includes advisory XML, import, and packed-layout questions without a checkout or failed build, and preserves the current framework and project system. Framework upgrades, legacy-project conversion, package-format migration, and C# source refactoring are outside this entry's scope.

The bundled references and specialist skills share MSBuild owners. Review shared-guidance updates against both surfaces and track applicable backports with their corresponding evals rather than maintaining independent guidance. This consolidation leaves specialist content unchanged; the bundled copy includes explicitly reviewed correctness fixes. Migrating or retiring the specialist plugin is a separate change.

The entry eval covers the three task lanes and out-of-scope requests. The normal plugin arm loads only dotnet. The supplemental coexistence experiment also exposes all dotnet-msbuild skills in its plugin arm, using the same stimuli and outcomes without prescribing which overlapping skill must win selection. Point EXPERIMENT_FILE at that experiment when running eng/run-skill-evals.sh dotnet msbuild. Inspect its activation traces for duplicate workflows and out-of-scope activation; the isolated arm's dormancy contract alone does not prove cross-plugin routing.

C# expert marketplace routing

csharp-expert routes a .NET request to an installed specialist or identifies the smallest dotnet/skills marketplace plugin that supplies a missing specialist. Its normal eval covers solution detection, marketplace acquisition, fallback behavior, and dormancy.

The supplemental csharp-expert-coexistence.experiment.yaml and csharp-expert-coexistence.claude.experiment.yaml load representative marketplace specialists in the plugin arm for GPT- and Claude-family executors. Run either without a skill filter:

EXPERIMENT_FILE=./csharp-expert-coexistence.experiment.yaml ./eng/run-skill-evals.sh
EXPERIMENT_FILE=./csharp-expert-coexistence.claude.experiment.yaml ./eng/run-skill-evals.sh

Inspect the plugin-arm activation traces to confirm that installed specialists are invoked without installation advice. This is trace evidence rather than a shared output grader because the target-only arm may legitimately identify a missing specialist after completing a safe fallback.