code-lens

code-lens

Gemini-powered MCP server for automated code review, analysis, and documentation.

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README

<!-- mcp-name: io.github.j0hanz/code-lens -->

Code Lens MCP Server

npm version License: MIT

Install in VS Code Install in VS Code Insiders Install in Visual Studio

Add to LM Studio Install in Cursor Install in Goose

Gemini-powered MCP server for automated code review, analysis, and documentation.

Overview

Code Lens is a Model Context Protocol server that uses Google Gemini to analyze diffs, review pull requests, detect code smells, generate documentation, and verify logic. It exposes 13 tools, 7 resources, and 5 prompts over stdio transport.

Key Features

  • PR review pipeline — generate diffs, assess impact, detect breaking API changes, and produce review summaries with merge recommendations
  • File analysis — load any source file for refactoring suggestions, code smell detection, documentation generation, and natural-language Q&A
  • Logic verification — verify algorithms using Gemini's code execution sandbox
  • Structured outputs — all tools return validated JSON via Zod v4 output schemas
  • Web search — Google Search with Grounding for up-to-date information retrieval
  • Task lifecycle support — every tool except load_file can run via MCP tasks with polling, cancellation, and progress updates

Requirements

Quick Start

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

Docker

docker run -i --rm -e GEMINI_API_KEY="your-api-key" ghcr.io/j0hanz/code-lens

Or with Docker Compose:

GEMINI_API_KEY=your-api-key docker compose up

Client Configuration

<details> <summary><b>Install in VS Code</b></summary>

Install in VS Code

Add to .vscode/mcp.json:

{
  "servers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

Or install via CLI:

code --add-mcp '{"name":"code-lens","command":"npx","args":["-y","@j0hanz/code-lens-mcp@latest"]}'

For more info, see VS Code MCP docs.

</details>

<details> <summary><b>Install in VS Code Insiders</b></summary>

Install in VS Code Insiders

Add to .vscode/mcp.json:

{
  "servers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

Or install via CLI:

code-insiders --add-mcp '{"name":"code-lens","command":"npx","args":["-y","@j0hanz/code-lens-mcp@latest"]}'

For more info, see VS Code Insiders MCP docs.

</details>

<details> <summary><b>Install in Cursor</b></summary>

Install in Cursor

Add to ~/.cursor/mcp.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Cursor MCP docs.

</details>

<details> <summary><b>Install in Visual Studio</b></summary>

Install in Visual Studio

Add to mcp.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Visual Studio MCP docs.

</details>

<details> <summary><b>Install in Goose</b></summary>

Install in Goose

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Goose MCP docs.

</details>

<details> <summary><b>Install in LM Studio</b></summary>

Add to LM Studio

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see LM Studio MCP docs.

</details>

<details> <summary><b>Install in Claude Desktop</b></summary>

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Claude Desktop MCP docs.

</details>

<details> <summary><b>Install in Claude Code</b></summary>

claude mcp add code-lens -- npx -y @j0hanz/code-lens-mcp@latest

Or add to config:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Claude Code MCP docs.

</details>

<details> <summary><b>Install in Windsurf</b></summary>

Add to ~/.codeium/windsurf/mcp_config.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Windsurf MCP docs.

</details>

<details> <summary><b>Install in Amp</b></summary>

amp mcp add code-lens -- npx -y @j0hanz/code-lens-mcp@latest

Or add to config:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Amp MCP docs.

</details>

<details> <summary><b>Install in Cline</b></summary>

Add to cline_mcp_settings.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Cline MCP docs.

</details>

<details> <summary><b>Install in Codex CLI</b></summary>

Add to ~/.codex/config.yaml:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Codex CLI MCP docs.

</details>

<details> <summary><b>Install in GitHub Copilot</b></summary>

Add to .vscode/mcp.json:

{
  "servers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see GitHub Copilot MCP docs.

</details>

<details> <summary><b>Install in Warp</b></summary>

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Warp MCP docs.

</details>

<details> <summary><b>Install in Kiro</b></summary>

Add to .kiro/settings/mcp.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Kiro MCP docs.

</details>

<details> <summary><b>Install in Gemini CLI</b></summary>

Add to ~/.gemini/settings.json:

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Gemini CLI MCP docs.

</details>

<details> <summary><b>Install in Zed</b></summary>

Add to ~/.config/zed/settings.json:

{
  "context_servers": {
    "code-lens": {
      "settings": {
        "command": "npx",
        "args": ["-y", "@j0hanz/code-lens-mcp@latest"]
      }
    }
  }
}

For more info, see Zed MCP docs.

</details>

<details> <summary><b>Install in Augment</b></summary>

Add to your VS Code settings.json under augment.advanced:

{
  "augment.advanced": {
    "mcpServers": [
      {
        "id": "code-lens",
        "command": "npx",
        "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
        "env": {
          "GEMINI_API_KEY": "your-api-key"
        }
      }
    ]
  }
}

For more info, see Augment MCP docs.

</details>

<details> <summary><b>Install in Roo Code</b></summary>

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Roo Code MCP docs.

</details>

<details> <summary><b>Install in Kilo Code</b></summary>

{
  "mcpServers": {
    "code-lens": {
      "command": "npx",
      "args": ["-y", "@j0hanz/code-lens-mcp@latest"],
      "env": {
        "GEMINI_API_KEY": "your-api-key"
      }
    }
  }
}

For more info, see Kilo Code MCP docs.

</details>

Use Cases

PR Review Pipeline

  1. Call generate_diff to capture unstaged or staged changes
  2. Run analyze_pr_impact to assess severity and breaking changes
  3. Run generate_review_summary for a risk rating and merge recommendation
  4. Run detect_api_breaking_changes to check for public API breakage
  5. Run generate_test_plan to produce prioritized test cases

Single-File Analysis

  1. Call load_file to cache a source file
  2. Run refactor_code for structural improvement suggestions
  3. Run detect_code_smells for Fowler-taxonomy anti-patterns
  4. Run generate_documentation to generate JSDoc/TSDoc stubs
  5. Use ask_about_code for natural-language Q&A about the file
  6. Use verify_logic to verify algorithms with code execution

Performance Audit

  1. Call generate_diff on a performance-sensitive change
  2. Run analyze_time_space_complexity to detect Big-O degradation

Research

  • Use web_search for up-to-date documentation or API references via Google Search with Grounding

Architecture

[MCP Client]
    │
    │ Transport: stdio
    ▼
[MCP Server: code-lens]
    │ Entry: src/index.ts → src/server.ts
    │
    ├── initialize / initialized (lifecycle handshake)
    │
    ├── tools/call ──────────────────────────────────────────────
    │   │
    │   │ Diff-based tools (require generate_diff first):
    │   ├── [generate_diff]              Sync — capture git diff
    │   ├── [analyze_pr_impact]          Flash — severity & impact
    │   ├── [generate_review_summary]    Flash — risk & merge rec
    │   ├── [generate_test_plan]         Flash — test cases
    │   ├── [analyze_time_space_complexity] Flash — Big-O analysis
    │   ├── [detect_api_breaking_changes]  Flash — API breakage
    │   │
    │   │ File-based tools (require load_file first):
    │   ├── [load_file]                  Sync — cache source file
    │   ├── [refactor_code]              Flash — refactoring
    │   ├── [detect_code_smells]         Flash — smell detection
    │   ├── [generate_documentation]     Flash — doc stubs
    │   ├── [ask_about_code]             Flash — Q&A
    │   ├── [verify_logic]               Flash — code execution
    │   │
    │   │ Standalone:
    │   └── [web_search]                 Flash — Google Search
    │
    ├── resources/read ──────────────────────────────────────────
    │   ├── [internal://instructions]        Server usage guide
    │   ├── [internal://tool-catalog]        Tool reference
    │   ├── [internal://workflows]           Workflow sequences
    │   ├── [internal://server-config]       Runtime config
    │   ├── [internal://tool-info/{name}]    Per-tool details
    │   ├── [internal://diff/current]        Cached diff (text/x-patch)
    │   └── [internal://file/current]        Cached source file
    │
    ├── prompts/get ─────────────────────────────────────────────
    │   ├── [get-help]           Full server instructions
    │   ├── [review-guide]       Tool + focus area workflow
    │   ├── [select-workflow]    Pipeline by change type
    │   ├── [analyze-file]       File analysis pipeline
    │   └── [tool-chain]         Tool prerequisite chain
    │
    └── Capabilities: structured output, tool annotations, notifications

Request Lifecycle

[Client] -- initialize {protocolVersion, capabilities} --> [Server]
[Server] -- {protocolVersion, capabilities, serverInfo} --> [Client]
[Client] -- notifications/initialized --> [Server]
[Client] -- tools/call {name, arguments} --> [Server]
[Server] -- notifications/progress {token, progress, total} --> [Client]
[Server] -- {content, structuredContent, isError?} --> [Client]

Task Lifecycle

  • generate_diff and load_file are sync-only. All other tools advertise taskSupport: optional.
  • Requestors may supply a task TTL. The server uses that value up to MAX_TASK_TTL_MS, or falls back to TASK_TTL_MS when omitted.
  • Cancelled tasks remain terminal as cancelled, and tasks/result returns a cancellation-shaped tool result.

MCP Surface

Tools

Tool Description Prerequisite Model
generate_diff Capture git diff (unstaged/staged) and cache server-side — Sync
analyze_pr_impact Assess severity, categories, breaking changes, rollback complexity generate_diff Flash
generate_review_summary PR summary, risk rating, merge recommendation generate_diff Flash
generate_test_plan Prioritized test cases and coverage guidance generate_diff Flash
analyze_time_space_complexity Big-O complexity analysis and degradation detection generate_diff Flash
detect_api_breaking_changes Detect breaking API/interface changes generate_diff Flash
load_file Cache a source file for analysis tools — Sync
refactor_code Complexity, duplication, naming, grouping suggestions load_file Flash
detect_code_smells Structural code smells (Fowler taxonomy) load_file Flash
generate_documentation JSDoc/TSDoc/docstring stubs for public exports load_file Flash
ask_about_code Natural-language Q&A about a cached file load_file Flash
verify_logic Verify algorithms via Gemini code execution sandbox load_file Flash
web_search Google Search with Grounding — Flash

Resources

URI Description MIME
internal://instructions Complete server usage instructions text/markdown
internal://tool-catalog Tool reference: models, params, outputs, data flow text/markdown
internal://workflows Recommended workflows and tool sequences text/markdown
internal://server-config Runtime configuration and limits text/markdown
internal://tool-info/{toolName} Per-tool details (parameterized) text/markdown
internal://diff/current Most recently generated diff text/x-patch
internal://file/current Most recently loaded source file text/plain

Prompts

Prompt Description
get-help Full server instructions: capabilities, tools, resources, constraints
review-guide Workflow guide for a specific tool and focus area
select-workflow Recommended tool pipeline based on change type
analyze-file Goal-based tool pipeline for single-file analysis
tool-chain Full prerequisite chain for a given tool

MCP Capabilities

Tool Annotations

All tools expose MCP tool annotations:

Annotation Used
readOnlyHint Yes
destructiveHint Yes
idempotentHint Yes
openWorldHint Yes

Structured Output

All Gemini-powered tools return validated structuredContent alongside text content, using Zod v4 output schemas.

Configuration

Variable Default Description
GEMINI_API_KEY — Required. Gemini API key. Falls back to GOOGLE_API_KEY.
GEMINI_MODEL gemini-3-flash-preview Override the default Gemini model for all tools.
MAX_DIFF_CHARS 120000 Maximum diff size in characters.
MAX_CONCURRENT_CALLS 10 Maximum concurrent Gemini API calls.
MAX_CONCURRENT_BATCH_CALLS 2 Maximum concurrent batch Gemini calls.
MAX_CONCURRENT_CALLS_WAIT_MS 2000 Wait timeout for concurrency semaphore.
TASK_TTL_MS 300000 Default task result retention in milliseconds when the request does not specify task.ttl.
MAX_TASK_TTL_MS 3600000 Upper bound for request-provided task TTL. Set to 0 to remove the cap.
GEMINI_BATCH_MODE off Enable Gemini batch mode.
GEMINI_HARM_BLOCK_THRESHOLD BLOCK_NONE Safety filter threshold (BLOCK_NONE, BLOCK_ONLY_HIGH, BLOCK_MEDIUM_AND_ABOVE, BLOCK_LOW_AND_ABOVE).
GEMINI_DIFF_CACHE_ENABLED false Enable Gemini context caching for large diffs.
GEMINI_DIFF_CACHE_TTL_S 3600 Cache TTL in seconds (when caching is enabled).

CLI Flags

npx @j0hanz/code-lens-mcp@latest --model gemini-2.5-flash --max-diff-chars 200000
Flag Env Equivalent
--model, -m GEMINI_MODEL
--max-diff-chars MAX_DIFF_CHARS

Security

Control Status
Input validation Zod v4 schema validation on all tool inputs
Path safety load_file restricts paths to workspace root
Stdout safety Logs to stderr; stdout reserved for MCP protocol
Non-root container Docker runs as dedicated mcp user

Development

npm install          # Install dependencies
npm run build        # Compile TypeScript
npm run dev          # Watch mode
npm run dev:run      # Run with --watch and .env
npm run start        # Run compiled server
npm run type-check   # Type-check src + tests
npm run lint         # ESLint
npm run test         # Run test suite
npm run format       # Prettier
npm run inspector    # MCP Inspector
npm run knip         # Dead code detection

Build and Release

  • CI: .github/workflows/release.yml
  • Docker: Multi-stage build (Dockerfile) with node:24-alpine
  • Docker Compose: docker-compose.yml
  • npm: Published as @j0hanz/code-lens-mcp

Troubleshooting

  • Missing API key: Set GEMINI_API_KEY or GOOGLE_API_KEY in your environment or client config env block.
  • "E_NO_DIFF" errors: Call generate_diff before running any diff-based review tool.
  • "E_NO_FILE" errors: Call load_file before running any file analysis tool.
  • Large diffs truncated: Increase MAX_DIFF_CHARS (default: 120,000 characters).
  • Stdout noise: Ensure no other processes write to stdout; the server uses stdio transport.

Credits

Contributing and License

MIT License. See LICENSE for details.

Contributions welcome via pull requests.

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