dotnet-coverage-mcp

<!-- mcp-name: io.github.Hyeonu-Cha/dotnet-coverage-mcp -->

   

An MCP (Model Context Protocol) server that gives AI assistants — Claude Code, Gemini CLI, and others — direct access to .NET test-coverage tooling. Run dotnet test, parse Cobertura XML, identify uncovered branches, diff coverage between runs, and append test code — all over stdio.

Purpose

This server lets an AI assistant run unit tests, collect coverage data, and analyse results — all without leaving the chat. Instead of manually running dotnet test and parsing reports, the AI can call the server's tools directly to:

• Discover source files and build smart batches by line budget
• Run a filtered set of tests and collect coverage
• Read compact, AI-optimised coverage summaries (method-level line/branch rates)
• Check per-file coverage against a configurable target rate (default 80%)
• Identify uncovered branches as structured JSON
• Diff coverage between runs to see only what changed
• Append new test code to an existing test file with atomic writes

How It Works

The server starts as a console process and communicates over stdio using the MCP protocol. An MCP-compatible client (Claude Code, Gemini CLI, etc.) launches the process and calls its tools as if they were functions.

AI Client  <--stdio/MCP-->  dotnet-coverage-mcp  <--shell-->  dotnet test + reportgenerator

Available Tools

| Tool | Description | |------|-------------| | GetSourceFiles | Discover .cs files from a file, folder, or .csproj project. Returns file metadata (lines, method count) and smart batches grouped by lineBudget. | | RunTestsWithCoverage | Run dotnet test with XPlat Code Coverage, generate a JSON summary via reportgenerator. Returns paths to Summary.json and coverage.cobertura.xml. Supports forceRestore and sessionId for concurrent isolation. | | GetCoverageSummary | Parse Summary.json into structured class/method coverage data sorted by branch coverage ascending (lowest first). | | GetFileCoverage | Get coverage for a single source file from Cobertura XML. Returns allMeetTarget (true when all classes meet the configured targetRate for both line and branch coverage; default 0.8). Supports sessionId. | | GetUncoveredBranches | Find uncovered branch conditions for methods matching a given name. Returns all matching methods with partial name support. Supports sessionId. | | GetCoverageDiff | Compare current Cobertura XML against baseline. Shows method-level changes including new and removed methods. Supports sessionId for concurrent isolation. | | AppendTestCode | Insert or append C# test code into a test file. Supports anchor-based insertion with whitespace-tolerant fallback matching. Uses atomic writes to prevent file corruption. | | CleanupSession | Remove session state files and TestResults/coveragereport directories. Pass sessionId to scope, or omit to clean artifacts older than maxAgeMinutes (default 120). |

Batch Workflow

For projects with many source files, the recommended workflow is:

1. Discover — Call GetSourceFiles on a folder or .csproj to get all files and smart batches
2. Run once — Call RunTestsWithCoverage with a broad filter (e.g., *) to collect coverage across all files
3. Check per-file — Call GetFileCoverage for each file in the current batch (instant XML parsing, no test re-run)
4. Focus — Pick the 3 lowest branch-coverage methods and call GetUncoveredBranches for each
5. Write tests — Use AppendTestCode to add test methods
6. Re-run and diff — Run tests once, call GetCoverageDiff to verify improvement
7. Repeat — Continue until batch files meet the target rate (default 80%) or 3 cycles with no improvement, then move to next batch

This minimises dotnet test invocations (the main bottleneck) while still tracking per-file progress.

Concurrency

Multiple AI agents can safely run in parallel against the same repository by passing a sessionId to each tool call:

• Isolated output directories — RunTestsWithCoverage creates TestResults-{hash}/ and coveragereport-{hash}/ per session, preventing one agent from deleting another's XML mid-parse
• Scoped state files — Coverage state is written to .mcp-coverage/.coverage-state-{hash}, so ResolveCoberturaPath resolves to the correct XML for each session
• Scoped baselines — GetCoverageDiff stores baselines as .coverage-prev-{hash}.xml per session
• Atomic writes — All file writes (state files and test code) use write-to-temp-then-rename to prevent corruption from race conditions or process crashes

Without sessionId, tools use shared defaults — safe for single-agent use.

Requirements

• .NET 9.0 SDK (or later) — https://dotnet.microsoft.com/download
• reportgenerator global tool — the server shells out to it to render coverage reports (installed in the Install step below)
• An MCP-compatible client (Claude Code, Gemini CLI, etc.)
• COVERAGE_MCP_ALLOWED_ROOT — recommended. Set to your repository root to restrict every tool's filesystem access to that subtree. Any path passed by the client outside this root is rejected with pathNotAllowed. When unset, the server logs a warning once and accepts any path (backward-compatible, but not recommended for shared environments).

  export COVERAGE_MCP_ALLOWED_ROOT=/path/to/your/repo

Install

Install the server as a global .NET tool from NuGet:

dotnet tool install --global dotnet-coverage-mcp

The server depends on the reportgenerator global tool to render coverage reports — install it too:

dotnet tool install --global dotnet-reportgenerator-globaltool

After install, the dotnet-coverage-mcp command is on your PATH.

Build & Run (from source)

cd <path-to-dotnet-coverage-mcp>

# Restore dependencies
dotnet restore

# Build
dotnet build

# Run
dotnet run

The server will start and wait for MCP messages over stdin/stdout.

MCP Client Configuration

After installing the global tool (dotnet tool install --global dotnet-coverage-mcp), register the server with your MCP client. Set COVERAGE_MCP_ALLOWED_ROOT to the repository you want the server to operate on.

Claude Code

claude mcp add coverage --env COVERAGE_MCP_ALLOWED_ROOT=/path/to/your/repo -- dotnet-coverage-mcp

Claude Desktop

Add to claude_desktop_config.json (Settings → Developer → Edit Config):

{
  "mcpServers": {
    "coverage": {
      "command": "dotnet-coverage-mcp",
      "env": {
        "COVERAGE_MCP_ALLOWED_ROOT": "/path/to/your/repo"
      }
    }
  }
}

Cursor

Add to ~/.cursor/mcp.json (global) or .cursor/mcp.json (per-project):

{
  "mcpServers": {
    "coverage": {
      "command": "dotnet-coverage-mcp",
      "env": {
        "COVERAGE_MCP_ALLOWED_ROOT": "/path/to/your/repo"
      }
    }
  }
}

VS Code (GitHub Copilot)

Add to .vscode/mcp.json:

{
  "servers": {
    "coverage": {
      "type": "stdio",
      "command": "dotnet-coverage-mcp",
      "env": {
        "COVERAGE_MCP_ALLOWED_ROOT": "/path/to/your/repo"
      }
    }
  }
}

Run from source

To run from source instead of the global tool, use dotnet run:

{
  "mcpServers": {
    "coverage": {
      "command": "dotnet",
      "args": ["run", "--project", "<path-to-dotnet-coverage-mcp>"],
      "transport": "stdio"
    }
  }
}

Or point directly at the compiled executable:

{
  "mcpServers": {
    "coverage": {
      "command": "<path-to-dotnet-coverage-mcp>\\bin\\Debug\\net9.0\\DotNetCoverageMcp.exe",
      "transport": "stdio"
    }
  }
}

Tool Parameters

GetSourceFiles

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | path | string | Yes | Path to a .cs file, folder, or .csproj project | | lineBudget | int | No | Max total lines per batch (default: 300). Small files are grouped together; large files get their own batch. |

RunTestsWithCoverage

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | testProjectPath | string | Yes | Full path to the .csproj test project | | filter | string | Yes | Test filter string (matched against FullyQualifiedName). Use or , for broad runs across multiple test classes. | | workingDir | string | No | Working directory; defaults to the project directory | | forceRestore | bool | No | When true, skips the --no-restore flag. Use after scaffolding a new test project or adding NuGet packages. | | sessionId | string | No | Isolates output directories (TestResults-{hash}/, coveragereport-{hash}/) and state files for concurrent multi-agent use. | | includeClass | string | No | Restrict coverage collection to types matching this name. Forwarded to coverlet as /p:Include=[]*{includeClass}. Always honored when set, independent of filter — pass an explicit value to scope coverage; omit it to collect coverage for everything the run touches. | | skipReport | bool | No | When true, skips the reportgenerator JSON-summary step and returns only the Cobertura XML path. Faster for the inner test loop, where GetFileCoverage/GetUncoveredBranches/GetCoverageDiff read the XML directly. Leave false (default) when you need GetCoverageSummary's Summary.json. |

GetCoverageSummary

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | summaryJsonPath | string | Yes | Full path to the generated Summary.json file |

GetFileCoverage

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | coberturaXmlPath | string | Yes | Path to coverage.cobertura.xml (falls back to .mcp-coverage/.coverage-state if not found) | | sourceFileName | string | Yes | Source file name to look up (e.g., ExampleService.cs) | | sessionId | string | No | Resolves session-scoped state file for concurrent isolation. | | targetRate | double | No | Coverage threshold (0.0–1.0) used to compute allMeetTarget. Default 0.8. |

GetUncoveredBranches

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | coberturaXmlPath | string | Yes | Path to coverage.cobertura.xml (falls back to .mcp-coverage/.coverage-state if not found) | | methodName | string | Yes | Method name to inspect (partial match supported; returns all matching methods) | | sessionId | string | No | Resolves session-scoped state file for concurrent isolation. |

GetCoverageDiff

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | coberturaXmlPath | string | Yes | Path to the current coverage.cobertura.xml | | workingDir | string | No | Directory for storing baseline; defaults to the XML's parent directory | | sessionId | string | No | Isolates baseline as .coverage-prev-{hash}.xml and resolves session-scoped state file. |

AppendTestCode

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | testFilePath | string | Yes | Full path to the target .cs test file | | codeToAppend | string | Yes | C# code to insert | | insertAfterAnchor | string | No | If provided, inserts code after the last occurrence of this string (with whitespace-tolerant fallback). If omitted, appends before the last }. |

CleanupSession

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | workingDir | string | Yes | Project working directory containing .mcp-coverage/ and TestResults artifacts | | sessionId | string | No | When set, removes only state files and directories scoped to this session. | | maxAgeMinutes | int | No | When sessionId is omitted, removes artifacts older than this many minutes. Default 120. |

State Files

All state files are written to a .mcp-coverage/ subdirectory inside the working directory, keeping the project root clean. Add .mcp-coverage/ to the target repository's .gitignore.

| File | Purpose | |------|---------| | .coverage-state | Default Cobertura XML path for single-agent use | | .coverage-state-{hash} | Session-scoped Cobertura XML path | | .coverage-prev.xml | Default coverage baseline for diff | | .coverage-prev-{hash}.xml | Session-scoped coverage baseline |

Plugin (Skills & Agent)

This repo includes a plugin/ directory with Claude Code skills and an agent definition for guided test coverage workflows:

plugin/
├── plugin.json
├── agents/
│   └── test-coverage.agent.md
└── skills/
    ├── scaffold-test-files/     — Create test directories and files mirroring source structure
    ├── run-coverage/            — Run tests and view coverage reports
    ├── analyze-coverage-gaps/   — Find uncovered branches and compare diffs
    └── improve-test-coverage/   — Iterative loop to reach 80% coverage

The skills support NUnit, xUnit, and MSTest with framework-agnostic reference docs in references/unit.md and references/integration.md.

Dependencies

| Package | Version | Purpose | |---------|---------|---------| | Microsoft.Extensions.Hosting | 10.0.7 | DI and hosting | | ModelContextProtocol | 1.2.0 | MCP server framework | | Microsoft.CodeAnalysis.CSharp | 5.3.0 | Roslyn AST for safe code insertion and accurate method counting (~15MB) |

Security

dotnet-coverage-mcp runs as a local stdio process and validates every tool argument against COVERAGE_MCP_ALLOWED_ROOT to confine filesystem access. See SECURITY.md for the threat model, hardening recommendations, and how to report a vulnerability.

Contributing

Contributions are welcome. See CONTRIBUTING.md for development setup, pull request guidelines, and code conventions. Notable changes are tracked in CHANGELOG.md.

Releasing

Maintainer-only — release process, NuGet publishing, and MCP registry submission are documented in RELEASING.md.