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README.md

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+# Turnstone MCP Server
+
+A [Model Context Protocol](https://modelcontextprotocol.io/) server providing four sandboxed, production-ready tools for LLM-driven workflows. Built with **FastMCP** and **Playwright**, it exposes code execution, headless browser automation, and file-to-Markdown conversion over HTTP.
+
+## Tools
+
+| Tool | Description |
+|---|---|
+| `execute_python_code` | Runs Python source in a subprocess with timeout, memory, and output-size limits |
+| `playwright_navigate` | Navigates a persistent headless Chromium session to a URL |
+| `playwright_get_page_text` | Extracts rendered text from the current browser page |
+| `extract_to_markdown` | Converts supported files (PDF, DOCX, images, CSV, etc.) to Markdown via `markitdown` |
+
+## Quick Start
+
+```bash
+# Install dependencies
+pip install fastmcp playwright markitdown
+playwright install chromium
+
+# Run the server
+python server.py
+```
+
+The server starts on `http://0.0.0.0:8000`. The MCP health endpoint is available at `/health`.
+
+## Configuration
+
+All limits are configurable via environment variables with sensible defaults:
+
+| Variable | Default | Description |
+|---|---|---|
+| `PYTHON_EXEC_TIMEOUT` | `30` | Python execution timeout (seconds) |
+| `PYTHON_MAX_OUTPUT` | `65536` | Maximum stdout/stderr capture (bytes) |
+| `PYTHON_MAX_MEMORY_MB` | `256` | Address-space memory limit per subprocess (MB) |
+| `PLAYWRIGHT_NAV_TIMEOUT` | `30000` | Browser navigation timeout (ms) |
+| `PLAYWRIGHT_TEXT_TIMEOUT` | `15000` | Page text extraction timeout (ms) |
+| `EXTRACT_MAX_FILE_SIZE` | `10485760` | Maximum file size for extraction (10 MB) |
+| `WORKSPACE_ROOT` | `/workspace` | Base directory for file-relative operations |
+
+Example with custom limits:
+
+```bash
+PYTHON_EXEC_TIMEOUT=60 PYTHON_MAX_MEMORY_MB=512 python server.py
+```
+
+## Architecture
+
+```
+┌──────────────┐     HTTP/MCP      ┌──────────────────┐
+│   LLM Client │ ────────────────► │  Turnstone MCP    │
+│              │                   │  Server :8000     │
+└──────────────┘                   └────────┬─────────┘
+                                            │
+                    ┌───────────────────────┼───────────────────────┐
+                    │                       │                       │
+              ┌─────▼─────┐          ┌──────▼──────┐       ┌───────▼───────┐
+              │ subprocess │          │ Playwright  │       │ markitdown    │
+              │ (Python)   │          │ Chromium    │       │ (file → MD)   │
+              └───────────┘          └─────────────┘       └───────────────┘
+```
+
+### Key design decisions
+
+- **Persistent browser session** — A singleton `PlaywrightBrowserManager` holds the Chromium process alive across tool calls, preventing garbage-collection teardowns.
+- **Sandboxed execution** — Python code runs in a separate process with a per-subprocess memory limit (`resource.setrlimit`) and a wall-clock timeout enforced by `subprocess.run`.
+- **Path traversal protection** — `extract_to_markdown` resolves all paths against `WORKSPACE_ROOT` and rejects anything that escapes it.
+- **Structured JSON logging** — All tool invocations and responses are logged as structured JSON for observability.
+- **CORS enabled** — The server accepts requests from any origin with standard MCP headers.
+
+## Endpoints
+
+| Method | Path | Description |
+|---|---|---|
+| `POST` | `/` | MCP protocol endpoint (default) |
+| `GET` | `/health` | Returns `{"status": "healthy", "service": "turnstone-mcp"}` |
+
+## Project Structure
+
+```
+server.py          # Complete MCP server — all logic in a single module
+```
+
+This repository is intentionally minimal: one file, zero dependencies beyond the pip requirements.
+
+## Development
+
+No test framework or build step is required. To add a new tool, follow the existing pattern:
+
+1. Define the function with `@mcp.tool()`
+2. Add docstring with `Parameters` and `Returns` sections
+3. Implement input validation and error handling
+4. Return a string result (success or error message)
+
+## License
+
+See the repository root for licensing information.