dotnet-mcp

An MCP (Model Context Protocol) server for .NET workspaces. It gives coding agents compiler-accurate symbol navigation, source-generator attribution, Avalonia/MAUI XAML queries, and a restricted Workspace Edit surface (rename / diagnostic fix / code refactoring). It is not a generic file writer, shell, or LSP proxy.

Package id on NuGet: Skymly.DotNetMcp (CLI command remains dotnet-mcp). Requires .NET 10+.

What it can do

• Load .sln / .slnx / .slnf / SDK-style .csproj / .vbproj / .fsproj
• C# and VB.NET via Roslyn; F# via an FCS stack beside the Roslyn snapshot
• Resolve a name to a checksummed SymbolHandle, then go to definition, members, references, implementations, callers, type hierarchy
• Attribute handwritten vs source-generated members (generator assembly + type + version)
• Project diagnostics; list generators / generated sources / generator diagnostics; list dynamic invocations
• Avalonia .axaml and MAUI .xaml: class, xmlns, x:Name, compiled-binding path, XAML diagnostics
• Restricted writes: preview then apply for rename, diagnostic fix (including project Fix all), and code refactoring

What it does not do

• Generic write / patch / create / delete file tools
• Shell, process, HTTP, or package-download tools
• WPF / WinUI XAML
• F# source-generator attribution, F# diagnostic fix, or F# code refactoring
• Extract-method / change-signature UIs
• Opening untrusted repositories safely — workspace_open runs MSBuild evaluation and project analyzers/generators

Tool names are locked by a snapshot test. Domain vocabulary: CONTEXT.md.

Quick Start

Trusted roots are required. The process working directory is never an implicit sandbox. On Windows, separate multiple roots with ;. You can also set DOTNET_MCP_TRUSTED_ROOTS.

The NuGet package Skymly.DotNetMcp is not published yet. Use a source build or a local pack until it is.

Development run

dotnet run --project src/DotNetMcp.Server -- --roots /path/to/repo

MCP client (stdio), from a clone of this repo:

{
  "mcpServers": {
    "dotnet-mcp": {
      "command": "dotnet",
      "args": ["run", "--project", "src/DotNetMcp.Server", "--", "--roots", "/path/to/repo"]
    }
  }
}

Local pack

dotnet pack src/DotNetMcp.Server -c Release -o ./artifacts
dotnet tool exec --source ./artifacts --yes Skymly.DotNetMcp -- --roots /path/to/repo

From NuGet (after the package is published)

Once Skymly.DotNetMcp is on nuget.org, dnx can become the preferred install path again:

dnx Skymly.DotNetMcp --yes -- --roots /path/to/repo

Equivalent after publish: dotnet tool exec Skymly.DotNetMcp --yes -- --roots /path/to/repo, or dotnet tool install -g Skymly.DotNetMcp then dotnet-mcp --roots /path/to/repo.

stdio only. Framework-dependent .NET tool; NativeAOT is not required.

Typical agent loop: workspace_open (returns immediately) → poll workspace_status until ready → symbol_resolve → navigation / attribution. Prefer a .slnf or a single project for a large solution.

MCP tools

Group	Tools
Workspace	workspace_open · workspace_status · workspace_list_projects · workspace_check_drift
Diagnostic fix	diagnostics_list_fixes · diagnostics_preview_fix · diagnostics_apply_fix
Symbol	symbol_resolve · symbol_summary · symbol_goto_definition · symbol_members · symbol_find_references · symbol_find_implementations · symbol_find_callers · symbol_type_hierarchy · symbol_attribution · symbol_preview_rename · symbol_apply_rename · symbol_list_refactorings · symbol_preview_refactoring · symbol_apply_refactoring
Project	project_diagnostics · project_list_generators · project_list_generated_sources · project_list_generator_diagnostics · project_list_dynamic_invocations
XAML	xaml_resolve_class · xaml_list_xmlns · xaml_resolve_name · xaml_resolve_binding · xaml_diagnostics

Security

1. Trusted roots — every path is canonicalized (including parent reparse points). Unresolvable links fail closed. Loaded project graphs and apply-paths are re-checked. Configure --roots or DOTNET_MCP_TRUSTED_ROOTS.
2. Open means execute — loading a solution runs MSBuild and referenced analyzers / source generators. Do not point this server at untrusted trees. .slnf project entries are checked before MSBuild opens them; .sln / .slnx / single-project graphs are checked after load, so an out-of-root ProjectReference is evaluated before it is rejected.
3. Default read + named writes — only rename / diagnostic fix / refactoring preview-apply. No generic write, command, or network tools.
4. Audit — local process logs (stderr under stdio). Tool name and path metadata only; no source text; no telemetry. Disable with DOTNET_MCP_AUDIT=0.

See ADR-0004.

Soft budgets and long-running load

List/scan tools honor a soft time budget (ADR-0003): they return partial results + nextCursor instead of hanging past the common ~60s client tools/call cap. Progress notifications are not a keepalive.

Environment variable	Default	Use
DOTNET_MCP_BUDGET_SINGLE_PROJECT_MS	5000	Single-project compile (e.g. project_diagnostics)
DOTNET_MCP_BUDGET_FIND_REFS_SCOPED_MS	5000	Scoped find-references
DOTNET_MCP_BUDGET_FIND_REFS_ENTIRE_MS	20000	Entire-solution find-references
DOTNET_MCP_BUDGET_BATCH_DIAGNOSTICS_MS	15000	Reserved batch diagnostics
DOTNET_MCP_BUDGET_FIXALL_PROJECT_MS	15000	Project Fix all; over budget fails the preview

Invalid values fall back to the defaults.

workspace_open never blocks the MCP request. Clients that do not opt into MCP Tasks should poll workspace_status. Details: spikes/s3-mcp-long-running/CONCLUSIONS.md.

Development / CI

Product and tests target net10.0. Fixtures include net8.0 / net9.0 projects (needed for MsBuildWorkspaceIntegrationTests).

dotnet restore DotNetMcp.slnx
dotnet build DotNetMcp.slnx -c Release --no-restore
dotnet test DotNetMcp.slnx -c Release --no-build

CI: .github/workflows/ci.yml (Ubuntu and Windows; product SDK via global.json 10.0.x roll-forward, fixture SDKs 8.0.x/9.0.x, pack + McpServer metadata check).

Product benches: docs/perf/benchmark.md.

dotnet run --project benches/DotNetMcp.Bench -c Release -- --suite fixtures
dotnet run --project benches/DotNetMcp.Bench -c Release -- --suite smoke

This repo uses mattpocock/skills; see AGENTS.md and docs/agents/.

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中文

面向 Agent 的 .NET MCP 服务器：C# / VB / F# 符号导航、源生成器归因、Avalonia/MAUI XAML、以及受限 Workspace Edit（rename / Diagnostic fix / Code Refactoring）。不是通用写文件、shell 或 LSP 代理。

NuGet 包 id 为 Skymly.DotNetMcp（命令名仍是 dotnet-mcp）。必须通过 --roots 或 DOTNET_MCP_TRUSTED_ROOTS 配置受信根，不再默认使用进程工作目录。workspace_open 会运行 MSBuild 与 analyzer/源生成器，不要对不受信任的仓库使用。

安装（包尚未上架，请先源码运行或本地 pack）：

dotnet run --project src/DotNetMcp.Server -- --roots /path/to/repo

NuGet 上架后可用：dnx Skymly.DotNetMcp --yes -- --roots /path/to/repo。