Test Coverage MCP

Make AI coding agents coverage-aware without wasting tokens

“Hey, I’m a coding agent. I just created flashy nifty feature… but oops, I downgraded the coverage 🤓. How could I know that?”

“Hey, I’m a testing agent. I was tasked to cover some code with testing, but how can I find which areas are not covered?😳”

Give your coding and testing agent eyes: MCP server that provides instant, reliable, token-efficient test coverage data for any programming language (LCOV based)

The Problem

When AI coding agents work on your code without proper coverage tooling, they face three critical issues:

1. Coverage Blindness - They can't see if their changes improved or regressed test coverage
2. Token Waste - They burn thousands of tokens trying to parse massive LCOV files (some exceed 50MB)
3. Unreliable Scripts - They improvise custom parsing scripts that often fail or produce incorrect results

The Solution

This MCP server solves all three problems by providing:

• Coverage Awareness - Agents can check coverage anytime with a simple tool call
• Token Efficiency - Get coverage summaries in <100 tokens instead of 10,000+
• Accuracy - Production-grade LCOV parsing that handles all format variations
• Baseline Tracking - Measure coverage progress within a session without keeping state in memory

Test Coverage: This project maintains 95% test coverage and we're targeting 100% soon.

Two Main Workflows

1. Query Coverage Summary

Ask for overall project coverage or coverage for specific files:

// Get overall project coverage
coverage_summary({ lcovPath: "./coverage/lcov.info" });
// Returns: { linesCoveragePercentage: 87.5, branchesCoveragePercentage: 82.1 }

// Get coverage for specific files
coverage_file_summary({
  lcovPath: "./coverage/lcov.info",
  filePath: "src/utils/parser.ts",
});
// Returns: { path: "src/utils/parser.ts", linesCoveragePercentage: 92.0, branchesCoveragePercentage: 88.5 }

2. Baseline Tracking for Session Progress

Establish a baseline at session start, then measure your progress:

// At session start - record current coverage as baseline
start_recording({ lcovPath: "./coverage/lcov.info" });
// Returns: "Recording started"

// ... agent writes code and tests ...

// Check coverage impact
get_diff_since_start({ lcovPath: "./coverage/lcov.info" });
// Returns: { linesPercentageImpact: +2.3, branchesPercentageImpact: +1.8 }

Why baseline tracking? Without it, agents would need to keep initial coverage in their stateful memory throughout the session, consuming valuable context window space.

Installation

npm install -g test-coverage-mcp

Configuration

Add this MCP server to your AI coding tool's configuration:

Claude Desktop (Claude Code)

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

{
  "mcpServers": {
    "test-coverage": {
      "command": "npx",
      "args": ["-y", "test-coverage-mcp"]
    }
  }
}

After updating, restart Claude Desktop.

Cursor IDE

Create or edit .cursor/mcp.json in your project root:

{
  "mcpServers": {
    "test-coverage": {
      "command": "npx",
      "args": ["-y", "test-coverage-mcp"]
    }
  }
}

GitHub Copilot (VS Code)

Create or edit .vscode/mcp.json in your workspace:

{
  "servers": {
    "test-coverage": {
      "command": "npx",
      "args": ["-y", "test-coverage-mcp"]
    }
  }
}

Requires VS Code 1.99+ or Visual Studio 17.14+. Enterprise users need "MCP servers in Copilot" policy enabled.

Windsurf (Codeium IDE)

macOS: Edit ~/.codeium/windsurf/mcp_config.json Windows: Edit %APPDATA%\Codeium\Windsurf\mcp_config.json Linux: Edit ~/.codeium/windsurf/mcp_config.json

{
  "mcpServers": {
    "test-coverage": {
      "command": "npx",
      "args": ["-y", "test-coverage-mcp"]
    }
  }
}

Or use the GUI: Settings → Advanced Settings → Cascade → Add Server

Available Tools

coverage_summary

Get overall project coverage from an LCOV file.

Input:

{
  lcovPath?: string  // Optional. Defaults to "./coverage/lcov.info"
}

Output:

{
  linesCoveragePercentage: number,      // 0-100
  branchesCoveragePercentage: number    // 0-100
}

Example:

coverage_summary({ lcovPath: "./coverage/lcov.info" });
// { linesCoveragePercentage: 87.5, branchesCoveragePercentage: 82.1 }

coverage_file_summary

Get coverage for a specific file.

Input:

{
  lcovPath?: string,  // Optional. Defaults to "./coverage/lcov.info"
  filePath: string    // Required. Path to the file
}

Output:

{
  path: string,
  linesCoveragePercentage: number,      // 0-100
  branchesCoveragePercentage: number    // 0-100
}

Example:

coverage_file_summary({
  lcovPath: "./coverage/lcov.info",
  filePath: "src/utils/parser.ts",
});
// { path: "src/utils/parser.ts", linesCoveragePercentage: 92.0, branchesCoveragePercentage: 88.5 }

start_recording

Record current coverage as a baseline for later comparison.

Input:

{
  lcovPath: string; // Required. Path to LCOV file to record
}

Output:

"Recording started";

Example:

start_recording({ lcovPath: "./coverage/lcov.info" });
// "Recording started"

get_diff_since_start

Compare current coverage against the recorded baseline.

Input:

{
  lcovPath: string; // Required. Path to current LCOV file
}

Output:

{
  linesPercentageImpact: number,      // Positive = improvement, negative = regression
  branchesPercentageImpact: number    // Positive = improvement, negative = regression
}

Example:

get_diff_since_start({ lcovPath: "./coverage/lcov.info" });
// { linesPercentageImpact: +2.3, branchesPercentageImpact: +1.8 }

Usage Examples

Example 1: Check Coverage Before Starting Work

Agent: "Let me check the current test coverage before I start working"
[Uses coverage_summary tool]
Agent: "Current coverage is 87.5% lines and 82.1% branches. I'll aim to maintain or improve this."

Example 2: Track Coverage Impact During Development

Agent: "I'll record the baseline coverage first"
[Uses start_recording tool]

Agent: "Now I'll add the new authentication feature with tests"
[Writes code and tests]

Agent: "Let me check the coverage impact"
[Uses get_diff_since_start tool]
Agent: "Great! Coverage increased by 2.3% for lines and 1.8% for branches."

Example 3: Verify Specific File Coverage

Agent: "Let me check coverage for the file I just modified"
[Uses coverage_file_summary with filePath: "src/auth/validator.ts"]
Agent: "The validator.ts file now has 95% line coverage and 92% branch coverage."

How It Works

This MCP server:

1. Parses LCOV files using a production-grade parser that handles all LCOV format variations
2. Calculates coverage percentages for overall project or individual files
3. Stores baselines in a temporary directory for session-based tracking
4. Returns compact JSON responses that consume minimal tokens

LCOV Format Support

This server supports all standard LCOV file formats, including:

• Files with summary sections (SF:, end_of_record)
• Files with line-by-line data only (DA: entries)
• Files with branch coverage data (BRDA:, BRF:, BRH:)
• Mixed formats within the same file

Troubleshooting

"LCOV file not found"

• Ensure you've run your test suite with coverage enabled first
• Check that the path to your LCOV file is correct (relative paths are resolved from current working directory)
• Default path is ./coverage/lcov.info

"No coverage data found for file"

• Verify the file path matches exactly as it appears in the LCOV file
• Some test frameworks use absolute paths, others use relative paths

"No baseline recording found"

• You must call start_recording before calling get_diff_since_start
• Baselines are stored in temporary storage and cleared when the system restarts

Development

# Install dependencies
npm install

# Build
npm run build

# Run tests (with coverage!)
npm test

# Run linter
npm run lint

# Test with MCP inspector
npm run inspect

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

MIT © Yoni Goldberg

Links

• GitHub Repository
• npm Package
• MCP Documentation
• Report Issues

Improvement ideas

• coverage_file_summary returns nested properties also declared as flat
• Start recording overrides other sessions files
• Improve record naming - setSessionBaseline, getDiffSinceBaseline