What it is

Gate Keeper is a pure MCP tool server that analyzes code (TypeScript/JS via SonarJS, C# via SonarAnalyzer.CSharp), assigns quality ratings (0–10), and exposes a live dependency graph through 7 MCP tools and a web dashboard.

The AI agent (Claude Code, Copilot, Cline, etc.) calls the MCP tools to understand code quality before editing and verify quality after edits. Gate Keeper provides the analysis — how the AI uses it is up to the agent and its tool-use policy.

Install

npm install -g @mohantn/gate-keeper

Installs two CLI commands: gate-keeper and gk.

Quick Start

gate-keeper setup            # Install deps, build, start daemon
gate-keeper daemon           # Start the daemon (ports 5378 / 5379)
gate-keeper mcp              # Start MCP server (stdio JSON-RPC)
gate-keeper dashboard        # Open http://localhost:5378/viz
gate-keeper status           # Check daemon health

| Command | Description | |---------|-------------| | gate-keeper setup | First-time setup: install deps, build, start daemon | | gate-keeper daemon | Start the daemon (ports 5378 / 5379) | | gate-keeper mcp | Start the MCP server (stdio JSON-RPC, consumed by AI agents) | | gate-keeper dashboard | Open the live dashboard in browser | | gate-keeper status | Check daemon health | | gk <command> | Short alias for any command |

MCP Tools — 7 Tools

All tools are available via a single MCP server: gate-keeper mcp

| Tool | Input | Output | When to use | |------|-------|--------|-------------| | register_repo | repo_path (required) | { repo, isNew, scanTriggered } | Session start — register the repo with the daemon | | get_quality_rules | None | Scoring thresholds and deduction rules (static) | Session start — understand what's enforced | | get_file_context | file_path (required), from_cache (optional, default false) | Full quality dossier: rating, violations, imports, dependents, trend | Before AND after editing a file | | get_method_context | file_path (required), method_name (optional) | Method-level blast radius: calls, dependents, all methods | Before editing a specific method | | get_dependency_graph | repo (optional) | Full graph in compact LLM-optimized format | Architecture analysis, full repo context | | get_graph_summary | repo (optional) | Pre-computed analytics: hotspots, worst files, coupling | Session start — codebase overview | | get_codebase_health | directory (optional), max_files (optional) | Avg rating, distribution, worst files, fix order | After bulk changes (3+ files) |

Key Behavioral Details

• register_repo — Only triggers a scan if the repo is new (no cached data). Safe to call multiple times.
• get_file_context — When from_cache=true fetches cached data from SQLite (fast). Default (false) runs a full analysis. External hook scripts should pass from_cache=true for pre-edit context and omit it for post-edit verification.
• get_dependency_graph — Returns the full graph which may be large. Use get_graph_summary for pre-computed analytics instead.

VS Code / Copilot / Cline Setup

Create .vscode/mcp.json in your project:

{
  "servers": {
    "gate-keeper": {
      "command": "gate-keeper",
      "args": ["mcp"]
    }
  }
}

Works with both global install and local clone — gate-keeper is always on PATH.

Architecture

AI Agent (Claude Code / Copilot / Cline)
    │
    ├── MCP tools via stdio JSON-RPC
    │     └── gate-keeper mcp
    │           └── 7 tools: register_repo, get_file_context, etc.
    │
    ▼
┌──────────────────────────────────────────────────────────────┐
│                     Daemon (port 5378 + 5379)                │
│                                                              │
│  IPC endpoints:  /repo-register, /analyze, /repos, /health  │
│  API endpoints:  /api/graph, /api/file-detail, /api/trends, │
│                  /api/cycles, /api/hotspots, /api/scan, ... │
│  WebSocket:      Live updates to dashboard clients           │
│                                                              │
│  UniversalAnalyzer pipeline:                                 │
│    readFile → MetricsExtractor → DependencyExtractor         │
│            → SonarJS/CSharpAnalyzer → CoverageAnalyzer       │
│            → RatingCalculator → SqliteCache → WebSocket      │
│                                                              │
└──────────────────────────────────────────────────────────────┘
    │
    ▼
┌──────────────────────────────────────────────────────────────┐
│               SQLite Cache (~/.gate-keeper/cache.db)         │
│  Tables: analyses, rating_history, repositories, positions   │
└──────────────────────────────────────────────────────────────┘

C# Analysis

Gate Keeper analyzes C# files (.cs) through a dual-mode system:

| Mode | When used | Capabilities | |------|-----------|-------------| | Roslyn | dotnet 8+ SDK detected | Full AST analysis: violations, type resolution, method calls | | Regex fallback | No dotnet SDK | Structural analysis: dependencies, metrics, method extraction |

Build the Roslyn analyzer:

npm run build:csharp

Quality Workflow

At session start:

// AI agent calls via MCP:
register_repo({ repo_path: "/path/to/project" })
get_quality_rules({})
get_graph_summary({})

Before editing a file:

get_file_context({ file_path: "/path/to/file.ts", from_cache: true })
get_method_context({ file_path: "/path/to/file.ts", method_name: "myFunction" })

After editing a file:

get_file_context({ file_path: "/path/to/file.ts" })
// ↑ This triggers re-analysis and returns the new rating

After bulk changes (3+ files):

get_codebase_health({ directory: "/path/to/project" })

Troubleshooting

| Symptom | Cause | Fix | |---------|-------|-----| | Daemon won't start | Missing runtime dependency or port conflict | Run npm install -g @mohantn/gate-keeper again, or kill processes on 5378/5379 | | Agent can't call MCP tools | MCP server not configured | Add .vscode/mcp.json or configure Claude Code settings | | get_file_context returns no data | Repo hasn't been registered yet | Call register_repo first to trigger initial scan | | Dashboard shows no data | Daemon not running or repo not scanned | Run gate-keeper daemon then call register_repo |

License

MIT — see LICENSE.