C# Class Analyzer MCP

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CSharpAnalyserMcp

A read-only Model Context Protocol (MCP) server that lets an AI assistant browse any C# solution through Roslyn.

The server loads a solution with MSBuildWorkspace into a cached Roslyn snapshot and then answers structured queries about it: where each type is declared, its XML documentation, and a method's signature, documentation, source location and body. An agent can therefore pull in the exact slice of source it needs instead of reading whole files into its context window.

• Transport: stdio (StdioServerTransport), protocol traffic on stdout only; all logs go to stderr.
• Solution path is passed on the command line (--workspace <path to .sln>); the solution is loaded before the MCP handshake, so a bad path fails fast with a message on stderr and a non-zero exit code.
• Tools declare structured output (UseStructuredContent), so results arrive as MCP structuredContent with camelCase JSON fields.
• Distribution: published to NuGet as the .NET tool CSharpAnalyserMcp (command csharp-analyser-mcp) and listed in the official MCP Registry as io.github.undy-mosq/CSharpAnalyserMcp.

Installation

NuGet .NET tool (recommended)

dotnet tool install --global CSharpAnalyserMcpcsharp-analyser-mcp --workspace D:\MyProject\MySolution.sln
# upgrade / removedotnet tool update --global CSharpAnalyserMcpdotnet tool uninstall --global CSharpAnalyserMcp

Install it globally: a --local install only writes a manifest entry, so csharp-analyser-mcp never lands on PATH and MCP clients cannot start it.

On demand with dnx (nothing to install, .NET SDK 10+)

# "--" separates dnx options from the arguments forwarded to the serverdnx CSharpAnalyserMcp --yes -- --workspace D:\MyProject\MySolution.sln

From source

git clone https://github.com/undy-mosq/CSharpAnalyserMcpdotnet build CSharpAnalyserMcp\CSharpAnalyserMcp.csprojdotnet run --project CSharpAnalyserMcp -- --workspace D:\MyProject\MySolution.sln

Requirements

Client configuration

The server is started with a single argument, --workspace, pointing at the solution file.

Installed .NET tool

The global tool shim lives in %USERPROFILE%\.dotnet\tools. MCP clients spawn the process themselves and only see the PATH they inherited, so point the configuration at the shim by absolute path (expand %USERPROFILE%, e.g. C:\Users\you\.dotnet\tools\csharp-analyser-mcp.exe):

Claude Desktop (claude_desktop_config.json):

{  "mcpServers": {    "csharp-analyser": {      "command": "C:\\Users\\you\\.dotnet\\tools\\csharp-analyser-mcp.exe",      "args": ["--workspace", "D:\\MyProject\\MySolution.sln"]    }  }}

VS Code (.vscode/mcp.json):

{  "servers": {    "csharp-analyser": {      "type": "stdio",      "command": "C:\\Users\\you\\.dotnet\\tools\\csharp-analyser-mcp.exe",      "args": ["--workspace", "D:\\MyProject\\MySolution.sln"]    }  }}

The bare command name ("command": "csharp-analyser-mcp") works only when that directory is already on the client's PATH; a client started before the tool was installed keeps the old environment, so restart it after changing PATH.

On demand with dnx (nothing installed)

{  "servers": {    "csharp-analyser": {      "type": "stdio",      "command": "dnx",      "args": ["CSharpAnalyserMcp", "--yes", "--", "--workspace", "D:\\MyProject\\MySolution.sln"]    }  }}

Append @<version> to the package id to pin a version. The MCP Server tab of the NuGet package page offers the same JSON for copying. dnx is a .cmd shim; if the client cannot spawn it, use the equivalent dotnet form instead: "command": "dotnet" with "args": ["tool", "exec", "CSharpAnalyserMcp", "--yes", "--", "--workspace", "D:\\MyProject\\MySolution.sln"].

Published executable

VS Code (.vscode/mcp.json):

{  "servers": {    "csharp-analyser": {      "type": "stdio",      "command": "C:\\Tools\\csharp-analyser\\CSharpAnalyserMcp.exe",      "args": ["--workspace", "D:\\MyProject\\MySolution.sln"]    }  }}

Running the project from source

{  "servers": {    "csharp-analyser": {      "type": "stdio",      "command": "dotnet",      "args": [        "run",        "--project",        "D:\\MyProject\\CSharpAnalyserMcp\\CSharpAnalyserMcp\\CSharpAnalyserMcp.csproj",        "--",        "--workspace",        "D:\\MyProject\\MySolution.sln"      ]    }  }}

Press F5 in VS Code to debug the server itself; .vscode/launch.json already passes a --workspace argument — point it at your own solution.

Tools

list_classes_in_folder

{ "folderPath": "src/Services", "kinds": ["class", "interface"] }

Files under bin/obj are skipped. For a partial type, the location of the first declaration is reported together with isPartial and declarationCount.

list_classes_in_namespace

{ "namespaceName": "MyApp.Services", "includeSubNamespaces": true, "kinds": ["all"] }

get_class_documentation

{ "className": "UserService", "maxXmlChars": 2000 }

get_method

{ "className": "DuelModel.RoleAttributes", "methodName": "SetEffect", "parameterTypes": ["RoleAttributes", "int"] }

Matching rules:

• Only members declared by the type itself are searched (ordinary methods; no inherited members, constructors or properties).
• Parameter types are compared case-insensitively and whitespace-insensitively, without namespace prefixes; C# aliases are mapped to their metadata names (int → Int32, string → String, …).
• The comparison is relaxed step by step: exact → ignoring generic arguments → allowing a prefix of the parameter list (optional parameters) → both.
• When nothing matches, matches is empty and candidates holds corrective hints: the same-named overloads of that type first, otherwise every method of that type.

reload_solution

No parameters. Discards the cached snapshot and re-opens the solution, so later queries see the current files on disk. Returns a WorkspaceInfo with reloaded: true and elapsedMilliseconds.

set_resolve_base_path

{ "basePath": "src" }

Type kinds and kinds

kind is lowercase and mutually exclusive: class, static class, record, struct, record struct, interface, enum, delegate. Only classes can be static, so class and static class are distinct; structs, enums, interfaces and delegates have no static form.

The kinds filter is case-insensitive and accepts multiple values (an omitted kinds behaves like ["class"]):

The same table is sent to the client as server-level instructions during the initialize handshake, so the model does not have to guess the accepted values.

Result shapes

All fields are serialized in camelCase.

ClassInfo (returned by list_classes_in_folder / list_classes_in_namespace):

ClassDocumentationInfo (get_class_documentation) carries className, namespace, kind, filePath, line, endLine, documentationXml and summary (both null when the type has no XML documentation).

MethodQueryResult (get_method) is { "matches": MethodInfo[], "candidates": string[] }, where every MethodInfo contains className, namespace, methodName, signature, returnType, parameterTypes, filePath, startLine, endLine, hasBody, isAbstract, isOverride, isExtension, documentationXml, summary, body.

WorkspaceInfo (reload_solution / set_resolve_base_path) is { "solutionPath", "resolveBaseDirectory", "projectCount", "reloaded", "elapsedMilliseconds" }.

Example — list_classes_in_folder with { "folderPath": "src/Services" }:

[  {    "className": "UserService",    "namespace": "MyApp.Services",    "kind": "class",    "filePath": "D:\\MyProject\\src\\Services\\UserService.cs",    "line": 12,    "endLine": 88,    "isPartial": false,    "declarationCount": 1,    "documentationSummary": "Provides user lookup."  }]

Output limits

Long payloads are truncated to keep tool results small; the appended marker reads ... [truncated: showing {n} of {m} chars]. All thresholds live in Services/TextTruncator.cs.

Passing 0 to maxXmlChars / maxBodyChars disables truncation for that call.

Typical workflow

1. Start the server once with --workspace pointing at your solution (an MCP client does this for you).
2. Discover types: list_classes_in_namespace { "namespaceName": "MyApp.Services" }, or list_classes_in_folder { "folderPath": "src/Services", "kinds": ["all"] }.
3. Read a type's contract: get_class_documentation { "className": "UserService" }.
4. Read the exact implementation: get_method { "className": "UserService", "methodName": "GetById", "parameterTypes": ["int"] }.
5. After the source files change, call reload_solution before the next query — otherwise queries keep answering from the stale snapshot.

Troubleshooting

• The server exits immediately with Solution file not found (or another MSBuild error) on stderr → the --workspace path is wrong; it must point at the solution file, not at a folder.
• The command "dnx" was not found in the client's MCP log → dnx ships with the .NET SDK 10 and newer. Install .NET SDK 10, or use an installed tool or the published executable instead.
• dotnet tool install reports that the package is not a .NET tool → the version you asked for was packed before PackAsTool was enabled; install the current version instead (dotnet tool list --global shows what is installed).
• spawn csharp-analyser-mcp ENOENT or MCP error -32000: Connection closed in the client log → the client could not resolve the command it was told to run. Use the absolute path to %USERPROFILE%\.dotnet\tools\csharp-analyser-mcp.exe (a --local install has no shim there at all) and restart the client.
• Cannot find package CSharpAnalyserMcp with version x.y.z right after a release → NuGet's index can lag behind the release. Retry later, or install from the downloaded .nupkg: dotnet tool install -g --add-source <folder> CSharpAnalyserMcp --version x.y.z.

Behavior notes and limitations

• Snapshot semantics. The solution is read once from disk; file edits become visible only after reload_solution. Unsaved editor buffers are never visible.
• Source-only view. Syntax trees under bin/obj are skipped, so types without source declarations are not reported.
• Declared members only. get_method does not walk base types, interfaces or the other parts of a partial type.
• Exact names. Type and method names must match exactly; namespaces are compared as full display strings. Use namespaceName (or a qualified className) to disambiguate.
• Cost. Every query asks each project for its compilation, so response time grows with solution size.
• Diagnostics. Workspace load problems are written to stderr as [WorkspaceFailed] {Kind}: {Message}; nothing but JSON-RPC ever reaches stdout.
• One solution per process. The workspace path is fixed at startup; start another instance to analyse another solution.

License

MIT — see LICENSE.

Building, publishing and the release process: docs/DEVELOPMENT.zh-CN.md (中文).