ghostlink

# GhostLink

**A security-hardened MCP server that gives AI coding agents safe, deterministic access to local repositories.**

## What is GhostLink?

GhostLink is a local-first [Model Context Protocol](https://modelcontextprotocol.io) server that exposes your codebase to AI coding agents through a small set of policy-gated tools. It solves a specific problem: AI agents need to search, read, patch, and verify code, but giving them raw shell access is a liability. GhostLink provides a sandboxed capability plane where every tool call is confined to a single repository root, every output follows a deterministic JSON shape, and every invocation is audit-logged.

## Why GhostLink?

| Capability | What it means |
|---|---|
| Secure local dev plane | Repo-root sandbox, no shell execution, JSONL audit trail on every tool call |
| Deterministic output | Same input produces the same JSON envelope shape -- enables golden tests and predictable agent consumption |
| Policy enforcement | Command allowlists, output caps, truncation flags, timeout enforcement -- the AI cannot do unbounded damage |
| Agent loop foundation | Built for the search, read, patch, verify cycle that autonomous coding agents run in a loop |
| Multi-server composition | One GhostLink instance per repo, composable with other MCP servers in the same client session |
| Production-ready Phase 2 base | Transport abstraction, schema versioning, and auth hook seams are preserved in the architecture today |

## Tools

| Tool | Description |
|---|---|
| `repo.search` | Ripgrep-powered regex search with glob filtering, deterministic ordering, and output caps (max 200 results) |
| `repo.read_file` | File read with size caps (max 10MB), binary detection, and truncation flags |
| `repo.apply_patch` | Unified diff patching with dry-run mode, full sandbox validation, and atomic rollback on failure |
| `repo.run` | Curated command execution (test, lint, typecheck, build, smoke) -- no arbitrary shell, allowlisted args only |
| `git.status` | Normalized git status with branch info, ahead/behind tracking, and sorted file entries |
| `git.diff` | Staged or unstaged diff with path filtering, sandbox validation, and output caps (max 2MB) |

Every tool returns a `ToolEnvelope`:

```json
{
  "ok": true,
  "data": { ... },
  "provenance": { "tool": "repo.search", "timestamp": "2026-02-24T...", "duration_ms": 42 }
}
```

On error, `"error": { "code": "...", "message": "..." }` replaces `"data"`. Full tool schemas: [docs/TOOLS.md](docs/TOOLS.md).

## Quick Start

### Prerequisites

- Node.js 18+
- ripgrep (`brew install ripgrep`)
- A git repository to expose

### Install and Build

```bash
git clone https://github.com/bgorzelic/ghostlink.git
cd ghostlink
npm install
npm run build
```

### Smoke Test (Raw STDIO)

GhostLink speaks JSON-RPC 2.0 over STDIO. Test it directly:

```bash
echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | \
  GHOSTLINK_REPO_ROOT=/path/to/target/repo node dist/index.js
```

This returns all 6 tools and their schemas.

### npm Package

```bash
npm install @bgorzelic/ghostlink
```

## Client Configuration

GhostLink works with any MCP client that supports STDIO transport.

### Claude Code

Create `.mcp.json` in the target repo root:

```json
{
  "mcpServers": {
    "ghostlink": {
      "command": "node",
      "args": ["/absolute/path/to/ghostlink/dist/index.js"],
      "env": {
        "GHOSTLINK_REPO_ROOT": "/path/to/target/repo"
      }
    }
  }
}
```

Then run `claude` in that directory. GhostLink tools appear as available MCP tools.

### Claude Desktop

Add to `~/Library/Application Support/Claude/claude_desktop_config.json`:

```json
{
  "mcpServers": {
    "ghostlink": {
      "command": "node",
      "args": ["/absolute/path/to/ghostlink/dist/index.js"],
      "env": {
        "GHOSTLINK_REPO_ROOT": "/path/to/target/repo"
      }
    }
  }
}
```

Restart Claude Desktop. GhostLink tools appear in the tool picker.

### Cursor, Windsurf, Cline, and Other MCP Clients

Add to your client's MCP server configuration:

```json
{
  "ghostlink": {
    "command": "node",
    "args": ["/absolute/path/to/ghostlink/dist/index.js"],
    "env": {
      "GHOSTLINK_REPO_ROOT": "/path/to/target/repo"
    }
  }
}
```

Consult your client's documentation for the exact config file location. The transport is always STDIO.

## Prompt Templates

[docs/PROMPTS.md](docs/PROMPTS.md) contains ready-to-use prompts for high-autonomy agent operation, including orchestrator prompts, sub-agent role definitions (Protocol Engineer, Toolsmith, Security Reviewer, Test Engineer, Docs Engineer), and multi-instance coordination patterns.

## Security Model

GhostLink enforces defense-in-depth at every layer:

- **Repo-root sandbox** -- All file operations confined to `GHOSTLINK_REPO_ROOT`. Path traversal, symlink escape, null bytes, and absolute paths outside the root are all rejected before any filesystem access.
- **No shell execution** -- `repo.run` uses `spawn` with `shell: false`. Commands are limited to a fixed allowlist (test, lint, typecheck, build, smoke) with per-command argument allowlists. Environment is stripped to six safe variables.
- **Output caps** -- Every tool that returns bulk data enforces hard maximums (200 search results, 10MB file reads, 200KB stdout/stderr, 2MB diffs). Truncation is flagged, never silent.
- **Atomic patch rollback** -- `repo.apply_patch` validates all paths and computes all patches before writing anything. If any write fails, completed writes are rolled back to their original state.
- **Timeout enforcement** -- `repo.run` kills processes at configurable timeouts (default 120s, hard cap 300s) with SIGTERM then SIGKILL.

Full threat model and mitigations: [docs/SECURITY.md](docs/SECURITY.md).

## Audit Logging

Every tool call produces a JSONL audit entry: `{ts, tool, ok, duration_ms, error_code?, repo_root}`.

| `GHOSTLINK_LOG` | Behavior |
|---|---|
| `stdout` (default) | JSONL audit lines written to stderr |
| `file` | JSONL written to `logs/ghostlink.jsonl` (auto-rotates at 10MB) |
| `off` | No logging |

Set via environment variable:

```bash
GHOSTLINK_LOG=file GHOSTLINK_REPO_ROOT=/path/to/repo node dist/index.js
```

## Development

```bash
npm install          # Install dependencies
npm test             # Run test suite (108 tests via Vitest)
npm run lint         # ESLint
npm run typecheck    # TypeScript strict mode check
npm run build        # Compile to dist/
npm run dev          # Dev mode with auto-reload (tsx watch)
```

Full verification after edits:

```bash
npm test && npm run lint && npm run typecheck && npm run build
```

## Documentation

| Document | Description |
|---|---|
| [docs/TOOLS.md](docs/TOOLS.md) | Canonical tool schemas (versioned public API) |
| [docs/SECURITY.md](docs/SECURITY.md) | Threat model and mitigations |
| [docs/QUICKSTART.md](docs/QUICKSTART.md) | Setup, smoke tests, and client configuration walkthrough |
| [docs/INSPECTOR.md](docs/INSPECTOR.md) | MCP Inspector manual testing guide |
| [docs/PROMPTS.md](docs/PROMPTS.md) | Agent prompts for orchestration and sub-agent roles |
| [docs/ROADMAP_DETAILED.md](docs/ROADMAP_DETAILED.md) | Full product roadmap with Phase 2 and Phase 3 deliverables |
| [docs/WHY_GHOSTLINK.md](docs/WHY_GHOSTLINK.md) | Strategic value proposition and architecture rationale |
| [docs/ENGINEERING_REPORT_v0.1.0.md](docs/ENGINEERING_REPORT_v0.1.0.md) | v0.1.0 ship report with milestone history and decision log |
| [templates/](templates/) | Ready-to-use CLAUDE.md and .mcp.json templates for target projects |

## Architecture

GhostLink is a three-layer stack designed for extensibility without core changes:

```
Transport (src/index.ts)        STDIO now, HTTP/SSE in Phase 2
    |
Server Factory (src/server.ts)  Transport-agnostic tool registration via MCP SDK + Zod schemas
    |
Tools (src/core/tools/*)        Six tools, each returning ToolEnvelope<T> through shared policy
    |
Policy (src/core/policy/*)      Sandbox enforcement, audit logging, output caps
```

The `createServer()` factory knows nothing about transport. Adding HTTP/SSE in Phase 2 means writing a new transport binding and auth middleware -- the server factory and all tool implementations remain unchanged. Phase 3 (agent runtime) adds memory resources and orchestration as consumers of GhostLink, not modifications to it.

## Roadmap

### Phase 1 -- Local STDIO [Shipped, v0.1.0]

Deterministic tool surface, repo-root sandbox, curated command execution, 108 tests, JSONL audit logging, npm package published.

### Phase 2 -- Remote Transport [Planned]

HTTP/SSE transport, OAuth 2.1 authentication, multi-user tenant separation, per-tenant rate limiting, schema versioning, structured audit logging with correlation IDs.

### Phase 3 -- Agent Runtime [Future]

Persistent memory resources exposed via MCP, optional policy-gated memory write tools, orchestration layer (external to GhostLink), evaluation loops, sub-agent coordination framework.

## License

ISC