Filesystem MCP Server

Implements configurable access control for file reading through a path allowlist/blocklist security model that validates all requested paths against configured boundaries before exposing file contents. Uses TypeScript SDK's tool registration pattern to expose read_file and list_directory tools with automatic path normalization and symbolic link resolution, preventing directory traversal attacks while maintaining transparent access semantics for LLM clients.

Provides write_file tool that creates or overwrites files with optional safety checks for preventing accidental data loss. Implements atomic write semantics by writing to a temporary file first, then renaming to target path, ensuring partial writes don't corrupt existing files. Respects the same path validation layer as read operations, preventing writes outside configured boundaries.

Implements list_directory tool that recursively enumerates directory trees with configurable depth limits and file type filtering. Returns structured metadata (size, modification time, permissions) for each entry without loading file contents, enabling efficient directory analysis. Uses TypeScript's fs.promises API with concurrent operations to traverse large directory structures while respecting path validation boundaries.

Provides move_file tool that relocates files or directories within the sandboxed filesystem with configurable behavior for handling destination conflicts (fail, overwrite, or rename). Validates both source and destination paths against the same security boundaries, ensuring moves cannot escape the allowed directory tree. Implements atomic move semantics using OS-level rename operations when possible.

Implements search_files tool that finds files matching patterns (regex, glob, or literal strings) across the allowed filesystem tree. Returns matching file paths with optional context snippets showing where matches occur. Uses efficient pattern matching libraries (e.g., minimatch for globs) to avoid loading entire files into memory, supporting large codebases with thousands of files.

Implements the MCP server-side tool registration pattern using TypeScript SDK, exposing filesystem operations as callable tools through JSON-RPC 2.0 protocol. Handles tool schema definition (input parameters, return types), request routing, and error serialization automatically. Supports multiple transport mechanisms (stdio, HTTP, WebSocket) through MCP's transport abstraction layer, allowing the same server to work with different client configurations without code changes.

Implements a declarative security model where filesystem access is controlled through configuration files specifying allowed_directories (allowlist) or denied_paths (blocklist). Configuration is loaded at server startup and applied to all subsequent requests without requiring code changes. Supports glob patterns and environment variable expansion in configuration paths, enabling flexible deployment across different environments (dev, staging, production).

Implements comprehensive error handling for filesystem operations with detailed diagnostic messages that help LLM clients understand why operations failed (e.g., 'Path /etc/passwd is outside allowed directories' vs generic 'Access denied'). Validates all inputs (paths, patterns, parameters) before execution and returns structured error responses through JSON-RPC error protocol, enabling clients to implement retry logic or fallback strategies.

Handles multiple concurrent MCP requests from clients through Node.js event loop and async/await patterns, ensuring each request is isolated and doesn't interfere with others. Uses TypeScript's Promise-based APIs to manage concurrent filesystem operations without blocking, enabling the server to handle multiple clients simultaneously. Maintains per-request state (e.g., current working directory context) without cross-request contamination.

Resolves symbolic links during path validation and directory traversal operations while detecting and preventing infinite loops caused by circular symlink chains. Uses path normalization and visited-set tracking to identify cycles before they cause stack overflow or infinite loops. Provides configuration options to either follow symlinks, reject them, or treat them as regular files depending on security requirements.