RoselineMCP

Roslyn code intelligence for AI coding agents, over MCP. Give Claude, Cursor, and Copilot a semantic view of your C# solution — symbols, references, call graphs, surgical edits — so they navigate by structure instead of re-reading source. Measured 85% fewer tokens (median) →

📖 Documentation, tool reference & the honest benchmark →

Table of Contents

• Why RoselineMCP
• Quick Start
• Features
• Tech Stack
• Getting Started
• MCP Client Compatibility
• Available Tools
• Tool Annotations
• Tool Compatibility Policy
• Architecture
• Project Structure
• Compile guard
• Security
• Documentation
• Roadmap
• Contributing
• License
• Acknowledgments

Why RoselineMCP

Your coding agent shouldn't read a 700-line file to change one method. Source code dominates an agent's token budget, so the cheapest win is to stop feeding it whole files.

RoselineMCP wraps the Roslyn compiler platform as an MCP server. Instead of dumping source into the model, it answers structural questions precisely — where is this symbol used, what implements this interface, who calls this method, what's the shape of this file — and it edits surgically: a member-level diff, not a whole-file rewrite.

On RoselineMCP's own source, the read-only navigation tools returned a median 85% fewer tokens per task (pooled, size-weighted: 93%) than reading the corresponding files — measured honestly, weak cases included.

search_symbols on Program.cs: 2,093 tokens → 120 (−94%). The agent gets the shape of the file; you skip the wall.

Quick Start

Any MCP client that speaks dnx (the .NET equivalent of npx) runs it on demand — no install step. Requires the .NET 10 SDK.

// claude_desktop_config.json  ·  .vscode/mcp.json  ·  ~/.cursor/mcp.json
{
  "mcpServers": {
    "roseline": { "command": "dnx", "args": ["RoselineMCP", "--yes"] }
  }
}

Then ask your agent to "find every caller of OrderService.Checkout" or "rename Foo to Bar across the solution." Prefer a pinned NuGet install or Docker? See Getting Started.

Features

• Token-efficient code navigation -- symbols, references, call graphs, type hierarchies, and file outlines via Roslyn instead of whole files. A measured 85% median token reduction per task (93% pooled, size-weighted) -- see the benchmark.
• Surgical code edits -- replace/add/delete a member or rename a symbol solution-wide, emitting a unified diff instead of a whole-file rewrite. Preview by default.
• Comprehensive analysis & auto-fix -- diagnostics across a solution (Roslyn + Roslynator) with automated fixes and reviewable patches.
• Read-only by default -- the seven navigation tools and the diagnostics/patch tools never touch disk; the three write tools require an explicit previewOnly: false.
• Compile guard (opt-in) -- a PostToolUse hook that puts the compiler's verdict behind every file write, not just RoselineMCP's own -- see Compile guard below.
• Works with your client -- Claude Desktop, VS Code (Copilot / MCP), Cursor. Install via dnx, NuGet global tool, or Docker.
• Honest, reproducible benchmark -- run it against your own solution: dotnet run --project RoselineMCP.TokenBenchmark -c Release.

Tech Stack

Versions above are kept in sync with RoselineMCP/RoselineMCP.csproj — that file is the source of truth if this table ever drifts.

Getting Started

Prerequisites

• NuGet global tool: .NET 10.0 SDK or later
• Docker: Docker Desktop or Docker Engine
• Build from source: .NET 10.0 SDK + MSBuild (included with Visual Studio or .NET SDK)
• MCP client: Claude Desktop or any MCP-compatible client

Installation

Claude Desktop, one click: download RoselineMCP.mcpb from the latest release and open it — Claude Desktop shows an install dialog, no config editing. (It launches via dnx under the hood, so the .NET 10 SDK is still required.) Prefer to edit config yourself, or using another client? Use one of the options below.

Option 1 -- dnx (no install step) (recommended)

RoselineMCP ships an MCP server registry manifest, so any MCP client that understands the dnx launcher (the .NET equivalent of npx — resolves and runs a NuGet-packaged tool on demand, without a separate dotnet tool install step) can start it directly. Requires the .NET 10.0 SDK.

{
  "mcpServers": {
    "roseline": {
      "command": "dnx",
      "args": ["RoselineMCP", "--yes"]
    }
  }
}

Add this to your Claude Desktop or VS Code MCP configuration (see MCP Client Compatibility below for exact file locations per client). dnx downloads and caches the tool on first use, so there's nothing to pre-install globally.

Option 2 -- NuGet Global Tool (offline / pinned-version installs)

Requires .NET 10.0 SDK or later.

dotnet tool install -g RoselineMCP

After installation, the roseline-mcp command is available globally.

Claude Desktop configuration (NuGet global tool)

Add to your Claude Desktop configuration file (claude_desktop_config.json):

{
  "mcpServers": {
    "roseline": {
      "command": "roseline-mcp"
    }
  }
}

Config file location:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Option 3 -- Docker

No SDK required. Works on any platform with Docker installed.

docker run -i --rm phmatray/roseline-mcp:latest

Claude Desktop configuration (Docker)

{
  "mcpServers": {
    "roseline": {
      "command": "docker",
      "args": [
        "run",
        "-i",
        "--rm",
        "phmatray/roseline-mcp:latest"
      ]
    }
  }
}

Note: The -i flag is required for stdio transport. The --rm flag removes the container after the session ends.

Option 4 -- Build from Source

git clone https://github.com/Atypical-Consulting/RoselineMCP.git
cd RoselineMCP
dotnet build
dotnet test

Claude Desktop configuration (build from source)

{
  "mcpServers": {
    "roseline": {
      "command": "dotnet",
      "args": ["run", "--project", "/path/to/RoselineMCP/RoselineMCP.csproj"]
    }
  }
}

MCP Client Compatibility

RoselineMCP speaks plain stdio MCP, so it should work with any MCP-compatible client. The snippets below are documented, not independently verified in every case — we've confirmed the protocol-level behavior (stdio transport, tool discovery, JSON responses) works correctly, but we have not personally exercised each client's own configuration UI/file end to end. If one of these doesn't work as written for your client version, please open an issue.

{
  "servers": {
    "roseline": {
      "command": "dnx",
      "args": ["RoselineMCP", "--yes"]
    }
  }
}

Available Tools

Every tool's description — the text an MCP client shows the model at tool-selection time — states its own Limitations: and shows one Example: call, within a test-enforced word ceiling; the thirteen tools with an optional project share one wording for the worktree caveat below, and resolvedPath is how you confirm which checkout actually answered. See docs/API.md § Tool description contract.

1. AnalyzeSolution

Analyzes an entire C# solution for diagnostics. Read-only — never modifies files on disk. pathOrGit also accepts an http(s):// Git URL, which is shallow-cloned to a temp directory, analyzed, and deleted afterward.

analyzeSolution({
  pathOrGit: "/path/to/solution.sln",
  include: "Core",              // Optional: only project names containing this substring
  exclude: "Test",              // Optional: skip project names containing this substring
  severity: "warning",          // Optional: minimum severity (Error|Warning|Info|Hidden)
  maxDiagnostics: 100           // Optional: Maximum diagnostics to return (default: 100)
})

Returns: solution file name, project count, a diagnosticSummary (counts by severity), a topDiagnostics array with project/file/line/column/id/severity/message per diagnostic, and analyzerLoad — present only when an analyzer reference failed to load or loaded without any C# analyzer (merged across the analyzed projects): failures are named and why, the benign rest only counted (referencesWithoutAnalyzers).

2. ListDiagnostics

Gets detailed diagnostics for a specific project. Read-only — never modifies files on disk. project is optional and accepts the same references as the navigation tools (name, directory, .csproj, .sln, or .slnx path); when omitted, the solution/project is auto-discovered from the working directory.

listDiagnostics({
  project: "MyProject.csproj",     // Optional: name, directory, .csproj, .sln, or .slnx; auto-discovered if omitted
  ids: ["CS0168", "CS0219"],       // Optional: Filter by diagnostic IDs
  files: ["Controller.cs"],        // Optional: substring match against each diagnostic's file path (case-insensitive; NOT a glob pattern)
  max: 50                          // Optional: Maximum results
})

Returns: project name, resolvedPath (the absolute .sln/.csproj actually loaded), totalDiagnostics count, the filtered diagnostics list, stats (counts grouped by ID and by severity), suggestedFixableIds — diagnostic IDs a code fix provider is actually registered for, whether it ships with Roslyn, in the bundled Roslynator catalog, or inside one of the project's own analyzer references — and analyzerLoad, which names every analyzer reference that failed to load (and why) — including a reference whose code fixers failed to load — plus a count of those that carry no C# analyzer, present only when there is something to say.

3. ApplyFixes

Applies automated code fixes for specified diagnostics. Defaults to preview mode: previewOnly defaults to true, so calling this tool without setting it never writes to disk — you must pass previewOnly: false explicitly to apply changes. project is optional and accepts the same references as the navigation tools (name, directory, .csproj, .sln, or .slnx path); when omitted, the solution/project is auto-discovered from the working directory. For a write (previewOnly: false) make it an absolute path — see the worktree note below.

applyFixes({
  ids: ["CS0168", "RCS1001"],   // Diagnostic IDs to fix
  project: "/repo/src/MyProject/MyProject.csproj",  // Optional; absolute for a write (see the worktree note)
  previewOnly: false             // Optional (default: true). Set false to write changes to disk.
})

Returns: project name, resolvedPath (the absolute .sln/.csproj actually loaded), fixedCount, fixersApplied (diagnostic IDs actually fixed), changedFiles (relative to resolvedPath's directory, forward slashes — the same path base as the navigation tools), a unified diff patch, notes (the scope — which project was fixed and which of the solution's projects were not analyzed, plus any linked file whose write reaches a sibling — and skipped/failed IDs and status messages), previewOnly echoing back what the caller asked for, applied (whether anything actually reached disk), verification — the compiler's verdict on the fixed code — and analyzerLoad (present only when a reference failed to load or loaded without analyzers, so "no diagnostics found for X" can be told apart from "the analyzer that reports X never loaded", and "no fixer" from "the fixer could not load"). Fixers are looked up in the Roslyn built-ins, then the bundled Roslynator catalog, then the project's own analyzer references; the bundled provider wins for an ID both carry.

A .sln target fixes one project — its primary project — and that scope is enforced on the write path, not only announced by the confirmation prompt: only the anchor project's documents are verified and written, and a caller who never sees a prompt (preview, a non-eliciting client, an unattended host) still reads which projects were skipped in notes. Pass a .csproj to fix a specific project — then nothing is reported as skipped, since that is what was asked for.

14. CheckCompilation

Answers "does this compile right now, and what broke" against on-disk state — the replacement for a dotnet build round trip in an agent's edit loop. Read-only, and compiler diagnostics only: analyzers cost several times a bare compile, which is the whole reason this tool is fast enough to run after every edit.

It reports on whatever is on disk, whoever wrote it, so it works just as well for edits made by other tools. The speed comes from the warm MSBuildWorkspace the server already holds: the first call of a session pays a cold load, every call after it reuses an incremental Roslyn compilation.

checkCompilation({
  project: "MyApp.sln",  // Optional: name, directory, .csproj, .sln, or .slnx; auto-discovered if omitted
  max: 20                 // Optional (default: 20). The rest are counted in `omitted`.
})

Returns: resolvedPath, compiles, errors (omitted when it compiles), omitted, scope (the projects compiled), scopeComplete and notes.

check_compilation vs list_diagnostics: check_compilation answers "is it still building?" — compiler errors, fast, for the edit loop. list_diagnostics answers "what should I clean up?" — analyzer diagnostics, statistics, and which IDs are auto-fixable. Reach for the first after an edit and the second when exploring.

15. SuggestFixExamples

For a diagnostic that no code fixer can repair, returns key examples: sites in the same solution, in the same syntactic and symbol shape, where the diagnostic does not fire, plus the rule's description and help link. Read-only and deliberately outside the compile-verification path: it proposes nothing, the agent writes the edit, and edit_member/apply_fixes still verify it.

suggestFixExamples({
  id: "CS0121",           // Required: the diagnostic ID
  project: "MyApp.sln",   // Optional: auto-discovered if omitted
  file: "Foo.cs",         // Optional: anchor on one occurrence (with line)
  line: 42,
  maxExamples: 3,         // Optional (default: 3)
  maxCandidates: 2000     // Optional (default: 2000)
})

Returns: resolvedPath, rule, hasFixer, alert (absent when the ID does not fire), examples, candidatesScanned, truncated and notes.

4. CreatePatch

Generates a unified diff between two text versions. Read-only — operates purely on the provided strings, never touches the filesystem.

createPatch({
  before: "original code",
  after: "modified code",
  fileName: "Example.cs",        // Optional: For display in diff
  ignoreWhitespace: false,       // Optional: ignore whitespace-only differences
  ignoreCase: false              // Optional: ignore case differences
})

Returns: the unified diff patch, hasChanges, linesAdded, linesRemoved, and the fileName/summary used in the diff header.

Code Navigation Tools (read-only)

These tools return precise structure instead of whole files, so an AI agent can orient itself in a codebase while spending far fewer tokens than reading source directly. All are read-only and take an optional project (name, directory, .csproj path, .sln, or .slnx path) — when omitted, RoselineMCP auto-discovers the solution/project from its working directory. When the project belongs to a solution, the whole solution is loaded and symbol search/resolution spans every project in it (including sibling projects the requested project doesn't reference), so references/renames span projects. Full request/response shapes are in docs/API.md.

Working in a git worktree? Auto-discovery is anchored to the server's working directory — the one the MCP client launched RoselineMCP in, fixed for the life of the process — not yours. What matters is only that the two differ, whether you walked into another checkout or were started in one: a worktree (e.g. .claude/worktrees/<name>) sits below the discovery walk's reach, so an omitted project resolves the main checkout instead. Every tool that takes an optional project — the seven navigation tools, both edit tools, listDiagnostics and applyFixes — reports resolvedPath, the absolute .sln/.csproj that actually answered — the .sln when the solution was loaded and contains the project, otherwise the .csproj that was opened directly (e.g. a project not listed in its nearest ancestor .sln). Check it, and pass an absolute path as project to target a specific checkout. (analyzeSolution is the exception: its pathOrGit is required, so it auto-discovers nothing.)

How you meet this depends on whether you are reading or writing. A read for something the other checkout does not have answers NotFoundError: Symbol not found: 'X'; a read for something it does answers successfully, with a resolvedPath you did not expect. Either way the failure envelope's error.resolvedPath names the checkout that was searched (omitted entirely when the call failed before resolving anything), so "not there" stays distinguishable from "wrong tree".

A write is not left to that: two checkouts of one repository mostly hold the same code, so a wrong-checkout write resolves, applies and returns an ordinary success in the tree you did not mean — disclosure that arrives only in the response to the call that already changed the file. So applyFixes, editMember and renameSymbol called with previewOnly: false and a project that is not an absolute path — omitted, blank, ".", a bare project name, a relative "App.sln" — are refused outright (ValidationError, nothing written, no prompt) when the resolved checkout belongs to a repository with linked worktrees — regardless of RoselineMCP:ConfirmDestructiveWrites. Only an absolute project steps past the refusal, because only an absolute path names a checkout: every other spelling resolves against the server's working directory, the very thing you don't know. See docs/API.md.

Relative file paths hang off resolvedPath. The navigation tools' file/definitionFile, applyFixes/editMember/renameSymbol's changedFiles and patch headers, and verification.errors[]/checkCompilation's errors[] file, are relative to the directory containing resolvedPath — so dirname(resolvedPath) + <returned path> is the real file, and a returned patch applies (git apply -p1) from that directory. That is the solution root in the usual case, and the project's own directory whenever a .csproj answered directly — including a project not listed in its nearest ancestor .sln. One exception: listDiagnostics/analyzeSolution report file absolute, so there is nothing to join. See docs/API.md.

Tool names on the wire are snake_case. The section headings below use friendly PascalCase/camelCase for readability, but the actual MCP tool names returned by tools/list (and expected by tools/call) are: search_symbols, get_symbol_info, find_references, find_implementations, get_call_graph, get_type_hierarchy, get_symbol_at_position, edit_member, rename_symbol (matching the existing analyze_solution / list_diagnostics / apply_fixes / check_compilation / create_patch).

5. SearchSymbols

Find symbols by wildcard/substring name pattern, or outline a single file.

searchSymbols({
  project: "MyApp.Core",
  query: "*Service",             // Substring, or wildcard with * and ? — omit to outline a file
  file: "UserService.cs",        // Optional: restrict to one file, or outline it when query omitted
  kinds: ["class", "method"],    // Optional: filter by kind (also accepts "type" / "member")
  max: 50                        // Optional (default: 50)
})

Returns: symbols (name, fullName, kind, signature, file, line — file is relative to resolvedPath's directory; the single-file outline instead returns name, kind, signature, line, containingType), totalFound, truncated (omitted when not capped).

6. GetSymbolInfo

The compact "go to definition": a symbol's declaration metadata and (optionally) its source.

getSymbolInfo({
  project: "MyApp.Core",
  symbol: "Acme.Users.UserService.GetUser",  // Simple or fully-qualified name
  includeSource: true                          // Optional (default: true)
})

Returns: name, fullName, kind, signature, and (each omitted when empty/absent) modifiers, baseTypes, interfaces, documentation, definitionFile/Line, and source. Accessibility is already part of signature; definitionFile is relative to resolvedPath's directory.

7. FindReferences

Every use site of a symbol across the solution, as location + one-line snippet.

findReferences({ project: "MyApp.Core", symbol: "GetUser", includeDefinition: false, max: 100 })

Returns: references (file — relative to resolvedPath's directory, line, snippet), totalReferences, truncated (omitted when not capped).

8. FindImplementations

Implementations of an interface/member, overrides of a virtual/abstract member, or derived types of a class.

findImplementations({ project: "MyApp.Core", symbol: "IRepository", max: 100 })

Returns: implementations (symbol summaries), totalFound, truncated.

9. GetCallGraph

A depth-bounded caller and/or callee graph for a method, with cycle detection.

getCallGraph({
  project: "MyApp.Core",
  method: "Handle",
  direction: "callers",   // "callers" (default) | "callees" | "both"
  depth: 1,               // 1-3 (default: 1)
  max: 50                 // Optional: nodes expanded per direction
})

Returns: callers/callees trees of nodes (fullName with simple parameter-type names, file — relative to resolvedPath's directory, line, truncated, children). Call GetSymbolInfo for a node's full signature.

10. GetTypeHierarchy

A type's base-class chain, implemented interfaces, and/or derived types.

getTypeHierarchy({
  project: "MyApp.Core",
  type: "SqlRepository",
  direction: "both",   // "base" | "derived" | "both" (default)
  max: 100             // Optional: maximum derived types returned (default: 100)
})

Returns: baseTypes, interfaces, derivedTypes (as symbol summaries).

13. GetSymbolAtPosition

The symbol living at a file:line(:column) position — turn a diagnostic, stack trace, or grep hit into a symbol name without reading the file.

getSymbolAtPosition({
  project: "MyApp.Core",
  file: "UserService.cs",  // File name or path suffix (same matching as SearchSymbols)
  line: 42,                // 1-based
  column: 17               // Optional (1-based) — omit to resolve the most relevant symbol on the line
})

Returns: name, fullName, kind, signature, isDeclaration (whether the position sits on the symbol's own declaration), and (each omitted when empty/absent) containingType, documentation, definitionFile/Line (relative to resolvedPath's directory). Line-only queries prefer declarations on the line over referenced symbols.

Code Editing Tools (preview by default)

Surgical edits that emit a member-level change rather than a whole-file rewrite. Like ApplyFixes, both default to preview mode (previewOnly: true) — nothing is written to disk unless you pass previewOnly: false explicitly.

11. EditMember

Replace, add, or delete a single type member; returns a unified diff.

editMember({
  project: "/repo/src/MyApp.Core/MyApp.Core.csproj",
  symbol: "Acme.UserService.GetUser",  // The member (replace/delete), or the container type (add)
  operation: "replace",                 // "replace" | "add" | "delete"
  newSource: "public User GetUser(int id) => _repo.Find(id);",  // Required for replace/add
  previewOnly: false                    // Optional (default: true). Set false to write to disk.
})

Returns: operation, target, changedFiles, patch, previewOnly, applied, notes.

12. RenameSymbol

Rename a symbol and update every reference across the solution (Roslyn rename); returns a unified diff.

renameSymbol({ project: "/repo/src/MyApp.Core/MyApp.Core.csproj", symbol: "GetUser", newName: "GetUserById", previewOnly: false })

Returns: symbol, newName, changedFiles, patch, previewOnly, applied, verification, notes.

Every write is compile-verified. Before edit_member, rename_symbol or apply_fixes touches disk, the candidate change is compiled in memory. If it introduces compiler errors — including in a downstream project you never named — the write is refused: the call still succeeds, applied comes back false, nothing is written, and you get the diff and the errors. Pass allowIntroducedErrors: true to write anyway. A repository that was already broken stays editable: the gate is what the change introduces, never whether the tree compiles. See Compile Verification for the scope rule and the guarantee boundary.

Tool Annotations

RoselineMCP's SDK (ModelContextProtocol 2.2.0) supports the standard MCP tool annotation hints (readOnlyHint, destructiveHint, idempotentHint), and every tool declares them via [McpServerTool(ReadOnly = ..., Destructive = ..., Idempotent = ...)]:

These hints are static per-tool metadata for MCP clients that surface them (e.g. to warn a user before an agent invokes a destructive tool) — they describe the tool's worst-case behavior, not the outcome of any specific call. See Tool Compatibility Policy below for the stability guarantees around tool names and parameters that these annotations sit on top of.

Tool Compatibility Policy

• Tool names and required parameters are stable within a major version. An MCP client integration written against AnalyzeSolution(pathOrGit, ...) on 1.x will keep working across all 1.x releases.
• Optional parameters may be added in minor versions (e.g. CreatePatch gained ignoreWhitespace/ignoreCase as optional, defaulted parameters without breaking existing callers).
• Renaming or removing a parameter, changing a parameter's required/optional status, or changing a tool's name is a breaking change. Breaking changes are called out under a dedicated "Breaking Changes" heading in CHANGELOG.md and only ship in a major version bump.
• Response shapes (JSON field names/types) are documented in docs/API.md and follow the same policy: additive fields are non-breaking, renamed/removed fields are breaking.

Supported Analyzers

The diagnostics tools (analyze_solution, list_diagnostics, apply_fixes) report compiler diagnostics plus analyzer diagnostics, executed via Roslyn's CompilationWithAnalyzers (check_compilation is deliberately not in this list — it is compiler-only, which is what makes it fast enough for an edit loop):

• Roslyn Analyzers -- Built-in C# compiler diagnostics
• Roslynator -- 500+ analyzers and fixes for C#, bundled with RoselineMCP (shipped as an analyzers/ folder next to RoselineMCP.dll) and executed by default, so RCS* diagnostics surface and are fixable out of the box
• Custom Analyzers -- Any Roslyn-based analyzer referenced by your analyzed solution is loaded from the project's analyzer references and run alongside the bundled ones (there is no built-in StyleCop.Analyzers reference — add it to your analyzed solution if you want SA* diagnostics). Their code fixers are loaded too: an analyzer-reported rule is auto-fixable when a matching fixer ships with Roslyn, in the bundled catalog, or inside one of the project's own analyzer references (the bundled one wins for an ID both carry).

What could not be loaded is named. Roslyn reports an analyzer reference it cannot load — one built against a newer Microsoft.CodeAnalysis than RoselineMCP's, a corrupt file — by contributing zero analyzers, not by failing. The three diagnostics responses carry an analyzerLoad block (analyzersRan, referencesConsulted, referencesContributing, referencesWithoutAnalyzers — references that loaded and declare no C# analyzer, counted rather than named — analyzersLoaded, and a notes[] entry per reference that failed: its name, the reason — load-failure with Roslyn's errorCode and message, unresolved (the assembly is not on disk, so it was removed from the loaded solution before Roslyn choked on it), exception, or, on list_diagnostics and apply_fixes, fixer-load-failure (its code fixers could not be loaded)). The block is omitted when every reference contributed and nothing failed, so a present one always says something; see docs/API.md.

Set RoselineMCP:RunAnalyzers to false for compiler-only diagnostics (faster on big solutions; see Configuration and the analyzer-execution note in SECURITY.md). The block is then present with analyzersRan: false, so "off" stays distinguishable from "all fine".

Examples

Analyzing a Solution

# Using with an MCP client
mcp call analyzeSolution '{
  "pathOrGit": "/Users/dev/MyProject/MyProject.sln",
  "severity": "warning",
  "maxDiagnostics": 50
}'

Response:

{
  "solution": "MyProject.sln",
  "projects": 5,
  "diagnosticSummary": {
    "error": 2,
    "warning": 15,
    "info": 28
  },
  "topDiagnostics": [
    {
      "id": "CS0168",
      "severity": "warning",
      "message": "The variable 'ex' is declared but never used",
      "file": "Program.cs",
      "line": 42
    }
  ]
}

Applying Fixes

mcp call applyFixes '{
  "project": "MyProject.Core.csproj",
  "ids": ["CS0168", "RCS1001"],
  "previewOnly": true
}'

Response includes a unified diff patch showing all changes that would be applied.

Configuration

RoselineMCP reads appsettings.json and appsettings.{Environment}.json from the directory the server binary is installed in (AppContext.BaseDirectory) — not from the process working directory. Launching the server from inside a target repository never picks up that repository's own appsettings.json, and the settings packaged with the dotnet tool install are always found. Configuration is read once at startup; there is no reload-on-change file watching.

Environment Variables

Environment variables prefixed with ROSELINE_ override the JSON files, using __ as the section separator. Settings under the RoselineMCP section therefore take a double prefix:

# RoselineMCP:EnableDiagnosticLogging
ROSELINE_RoselineMCP__EnableDiagnosticLogging=true

# RoselineMCP:DefaultTimeout (ms)
ROSELINE_RoselineMCP__DefaultTimeout=300000

# RoselineMCP:RunAnalyzers (compiler-only diagnostics when false)
ROSELINE_RoselineMCP__RunAnalyzers=false

# RoselineMCP:ConfirmDestructiveWrites (no elicitation before writes; unattended hosts)
ROSELINE_RoselineMCP__ConfirmDestructiveWrites=false

# RoselineMCP:ConfirmDestructiveWritesTimeout (ms to wait for that confirmation; 0 = forever)
ROSELINE_RoselineMCP__ConfirmDestructiveWritesTimeout=300000

# Logging:LogLevel:RoselineMCP
ROSELINE_Logging__LogLevel__RoselineMCP=Debug

• DOTNET_ENVIRONMENT: Set environment (Development, Production)

appsettings.json

Configure logging and other settings:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "RoselineMCP": "Debug"
    }
  },
  "RoselineMCP": {
    "DefaultTimeout": 120000,
    "EnableDiagnosticLogging": false,
    "WorkspaceCache": true,
    "RunAnalyzers": true,
    "ConfirmDestructiveWrites": true,
    "ConfirmDestructiveWritesTimeout": 300000
  }
}

• RoselineMCP:DefaultTimeout: Wall-clock analysis budget (ms) applied to each tool call, in addition to the caller's own cancellation. 0 disables it. On the three write tools it does not cover the whole invocation: when a write confirmation is elicited, this clock starts only after the human answers, so think-time is charged to ConfirmDestructiveWritesTimeout instead. Size it for the analysis, not for the span a caller observes.
• RoselineMCP:EnableDiagnosticLogging: Opt-in, local-only tracing of tool invocations — see Debug Logging. Disabled by default; enabled in appsettings.Development.json.
• RoselineMCP:WorkspaceCache: Reuse the loaded MSBuild workspace across navigation/edit tool calls (enabled by default) — see Performance. Set to false to load a fresh workspace on every call. This is an isolation/debugging switch, not a memory-saving one — measured, disabling it costs ~26% more resident memory and ~45× second-call latency; see Memory Management.
• RoselineMCP:RunAnalyzers: Run Roslyn analyzers (bundled Roslynator + the target project's own analyzer references) in the diagnostics tools (enabled by default) — see Supported Analyzers. Set to false for compiler-only diagnostics.
• RoselineMCP:ConfirmDestructiveWrites: Ask the client to confirm (via MCP elicitation) before a write tool actually writes, when the caller passed previewOnly: false (enabled by default). Set to false for unattended hosts — CI, headless agents, or any client that cannot answer an elicitation — in which case the explicit previewOnly: false opt-in is the only guard before a write.
• RoselineMCP:ConfirmDestructiveWritesTimeout: How long (ms) to wait for that confirmation before treating the silence as "no" and returning a preview (default 300000, 5 minutes). It is deliberately not DefaultTimeout — that is an analysis budget, and a human reading a real diff may legitimately exceed it. A client that accepts the prompt and never answers used to block the tool call forever; set this to 0 or less to restore that unbounded wait.

Architecture

RoselineMCP uses stdio transport — this is an intentional design decision. The server runs as a local process launched by the MCP client (Claude Desktop, AI agents), communicates over stdin/stdout, and exits when the client disconnects (except while a write confirmation is pending, where it lingers until ConfirmDestructiveWritesTimeout expires, or indefinitely if that is 0 — see docs/ARCHITECTURE.md). This makes it perfectly suited for distribution as a NuGet global tool (dotnet tool install -g RoselineMCP) or Docker image — no port binding, no HTTP server, no infrastructure to manage.

┌─────────────────────┐
│   MCP Client        │
│  (Claude Desktop,   │
│   AI Assistants)    │
└────────┬────────────┘
         │ MCP Protocol (stdio)
         ▼
┌─────────────────────┐
│   RoselineMCP       │
│   MCP Server        │
│                     │
│  ┌───────────────┐  │
│  │  Tool Layer   │  │
│  │  (Analyze,    │  │
│  │   Fix, Patch) │  │
│  └───────┬───────┘  │
│          ▼          │
│  ┌───────────────┐  │
│  │ Service Layer │  │
│  │ (Workspace,   │  │
│  │  Diagnostics) │  │
│  └───────┬───────┘  │
│          ▼          │
│  ┌───────────────┐  │
│  │ Roslyn +      │  │
│  │ Roslynator    │  │
│  │ Analyzers     │  │
│  └───────────────┘  │
└─────────────────────┘
         │
         ▼
┌─────────────────────┐
│  C# Source Code     │
│  (.sln / .csproj)   │
└─────────────────────┘

Project Structure

RoselineMCP/
├── RoselineMCP/
│   ├── Interfaces/       # Service interfaces
│   ├── Services/         # Core business logic
│   ├── Tools/            # MCP tool implementations
│   ├── Models/           # Data transfer objects
│   └── Program.cs        # Application entry point
├── RoselineMCP.Tests/    # Unit tests
├── .github/workflows/    # CI/CD pipelines
├── Dockerfile            # Container build
└── RoselineMCP.sln       # Solution file

Performance

• Workspace Cache -- The navigation, edit, and diagnostics/fix tools (ListDiagnostics, ApplyFixes, and everything backed by IProjectLoader) reuse the loaded MSBuildWorkspace across calls, cutting hundreds of milliseconds of reload off every call after the first. Cached entries are fingerprinted (last-write-time + size of the .sln, every .csproj, and every source file, plus their directories) and re-checked on each call, so any change on disk — including RoselineMCP's own edits — triggers a fresh reload. A file/directory whose own last write was still fresh when its stamp was captured also gets a content signature (a hash, or a directory listing) recorded alongside it, so a same-length write landing in the same filesystem-timestamp bucket is still caught by comparing that signature rather than trusted on a bare stat match — cheaply, without forcing a reload on every call while the file stays fresh. Disable with RoselineMCP:WorkspaceCache = false — but note that this is an isolation/debugging switch, not a way to reduce memory: a disposed workspace's memory is not returned to the OS, so disabling the cache measures ~26% worse on resident memory as well as ~45× slower. The measured profile — and why an idle-release was evaluated and rejected — is in Memory Management
• Workspace Isolation (AnalyzeSolution) -- AnalyzeSolution still creates a fresh MSBuildWorkspace per operation (see Architecture)
• Sequential Project Analysis -- Projects within a solution are analyzed one at a time, not concurrently, to keep MSBuild workspace state consistent
• Result Capping -- maxDiagnostics/max bound how many diagnostics are returned per call, independent of how many were found

Compile guard

The compile gate behind EditMember/RenameSymbol/ApplyFixes only fires on writes made through those tools. The compile guard puts the same verdict behind every file write in a C# solution — Edit, Write, MultiEdit, whatever your agent reached for — by running as a PostToolUse hook that asks the already-running server for a verdict over a local socket.

It reports; it cannot block. PostToolUse fires after the tool has written, and the hook contract carries no blocking decision. What the guard does is surface the introduced compiler errors to the agent inside the same turn, so the next thing it does is repair them instead of building on top of them. Preventing the write is not on offer — see the issue for why the alternative that can block was rejected.

Turn it on (it is off by default), then install the hook:

# 1. the server opens the local guard endpoint
export ROSELINE_RoselineMCP__Guard=true

# 2. print the settings.json block and paste it into .claude/settings.json
roseline-mcp guard --print-hook

What it does on each write:

Compiler diagnostics only, and scoped to the changed project plus its dependents, so it is fast enough to sit in an inner loop. It adds a local IPC endpoint: read SECURITY.md before enabling it on a shared machine.

Security

• Read-Only by Default -- AnalyzeSolution, ListDiagnostics, CreatePatch, and all six code navigation tools (SearchSymbols, GetSymbolInfo, FindReferences, FindImplementations, GetCallGraph, GetTypeHierarchy) never write to disk. The three write-capable tools — ApplyFixes, EditMember, and RenameSymbol — each default to previewOnly: true; writing requires the caller to pass previewOnly: false explicitly. Behind that opt-in sits a second, best-effort guard: the write tools ask the client to confirm via MCP elicitation before writing, and a decline downgrades the call to a preview. So does an unanswered prompt — the round-trip is bounded by RoselineMCP:ConfirmDestructiveWritesTimeout (default 5 minutes), after which the call returns a preview rather than writing or hanging. That confirmation is skipped when the client cannot elicit, and an operator can disable it outright with RoselineMCP:ConfirmDestructiveWrites=false — after which previewOnly: false is the only guard left. See SECURITY.md.
• Real, Read-Only Git Cloning -- pathOrGit accepts http(s):// Git URLs, which are shallow-cloned (git clone --depth 1) into a temp directory that's deleted after the operation. No other URL scheme is treated as a Git remote.
• MSBuild Is Not a Sandbox -- loading a .sln/.csproj via MSBuildWorkspace is a design-time MSBuild evaluation and can execute build logic embedded in the project (<Exec> tasks, custom UsingTask assemblies, imported .targets/.props). Analyzing a fully untrusted repository or URL carries a real code-execution risk on the host. See SECURITY.md for the full write-up and operator recommendations before pointing RoselineMCP at untrusted input.
• Analyzer Execution Is Code Execution -- the diagnostics tools also run the target project's own referenced Roslyn analyzers in-process (see Supported Analyzers); an analyzer from an untrusted repository is arbitrary code. RoselineMCP:RunAnalyzers = false disables the diagnostic analyzer pass (bundled Roslynator included). See SECURITY.md.
• Code-Fix Providers Come From Those Same References -- list_diagnostics and apply_fixes also load the CodeFixProvider types a project's own analyzer references carry. That adds no assembly the analyzer pass does not already load (each is obtained through the reference's own assembly loader), but it is a decision rather than an accident, and RunAnalyzers = false does not govern it. Recorded in SECURITY.md.
• Source Generators Run Regardless Of That Switch -- generators ship through the same AnalyzerReferences, but run as part of building any compilation rather than as part of the diagnostics pass, so every semantic path executes them -- all navigation tools included. They cannot be suppressed without breaking semantic analysis. RunAnalyzers = false narrows the code-execution surface of an untrusted repository; it does not close it. Isolate instead -- see SECURITY.md.
• No Dedicated Path-Traversal Sandbox -- paths are resolved with plain existence checks, not canonicalized against an allowed root; treat pathOrGit/project/branch as trusted operator input.

Troubleshooting

Common Issues

1. MSBuild not found: Ensure .NET SDK is installed and in PATH
2. Solution won't load: Check for missing NuGet packages, run dotnet restore
3. No analyzer (RCS/SA) diagnostics found**: Verify RoselineMCP:RunAnalyzers isn't set to false; for non-bundled rule sets (e.g. StyleCop), verify the analyzer is installed in the target project
4. Permission denied: Ensure read access to solution files

Debug Logging

Enable detailed logging:

ROSELINE_Logging__LogLevel__RoselineMCP=Debug dotnet run --project RoselineMCP/RoselineMCP.csproj

Tracing Individual Tool Calls

Every tool call gets a per-invocation correlation ID (a GUID). It's cheap to generate so it's always created, but it's only surfaced when you need it: it's included in every JSON error response (correlationId) and attached to that call's log lines via ILogger.BeginScope, so a user reporting a failure can hand you one ID that ties back to the full server-side log entry — without needing to grep timestamps.

For deeper, opt-in tracing of each tool invocation (start/stop, duration, success/failure) as a System.Diagnostics.Activity span, set RoselineMCP:EnableDiagnosticLogging to true (it's already true in appsettings.Development.json):

ROSELINE_RoselineMCP__EnableDiagnosticLogging=true dotnet run --project RoselineMCP/RoselineMCP.csproj

This uses the built-in ActivitySource/Activity APIs rather than the OpenTelemetry SDK, so it adds no extra dependency. Spans are logged exclusively through the existing ILogger pipeline, which is already routed to stderr — never to stdout (the MCP JSON-RPC channel) — and nothing is ever sent over the network; when the flag is off (the default), no listener is registered and the spans cost essentially nothing.

Roadmap

• Additional analyzer rule sets (SonarAnalyzer, FxCop)
• Auto-fix suggestions with confidence scoring
• CI/CD integration for automated analysis pipelines
• Multi-solution support in a single session
• Incremental analysis (only changed files)
• Custom analyzer rule configuration via MCP

Want to contribute? Pick any roadmap item and open a PR!

Documentation

• Documentation site -- overview, tool reference, and the token-savings benchmark (built from website/, deployed to GitHub Pages)
• docs/API.md -- Full request/response reference for every MCP tool, service interfaces, models, and the error-response contract
• docs/AGENT-BENCHMARK.md -- End-to-end A/B: does an AI agent actually spend fewer tokens with RoselineMCP? (honest answer — a large-codebase win, break-even on small)
• docs/ARCHITECTURE.md -- Layered architecture, data flow, and design patterns
• PROMPTS.md -- Example prompts and end-to-end workflows for each tool
• CHANGELOG.md -- Release history and breaking changes
• SECURITY.md -- Vulnerability reporting and the MSBuild code-execution caveat
• CONTRIBUTING.md -- Development setup and PR process

Atypical MCP servers

Part of a suite of Model Context Protocol servers by Atypical Consulting:

• RoselineMCP — Roslyn code intelligence for AI agents
• ASTral — structured code retrieval (tree-sitter)
• AdrMcp — Architecture Decision Records over MCP
• MarkdownInk — Markdown rendering for the terminal

Contributing

Contributions are welcome! Please read CONTRIBUTING.md first.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit using conventional commits (git commit -m 'feat: add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

License

MIT © 2026 Atypical Consulting SRL

Acknowledgments

• Built on Roslyn -- The .NET Compiler Platform
• Powered by Roslynator -- C# analyzers and refactorings
• Uses DiffPlex -- Diff generation library
• Implements Model Context Protocol -- AI assistant integration protocol

Built with care by Atypical Consulting -- opinionated, production-grade open source.

Built by Atypical Consulting. We also make NuGetKeep, a self-hosted NuGet server with supply-chain quarantine.