Proposal: Environment Variable Configuration for Filesystem MCP Server

Proposal: Environment Variable Configuration for Filesystem MCP Server

Overview

Currently, the Filesystem MCP Server only supports configuring allowed and denied directories through command-line arguments. This approach can become unwieldy and hard to manage when complex configurations are needed. I propose adding support for environment variable-based configuration to improve usability.

Proposed Changes

Allow configuration of allowed and denied directories through the following environment variables:

• ALLOWED_DIRS: Semicolon-separated list of allowed directories
• ALLOWED_READONLY_DIRS: Semicolon-separated list of read-only allowed directories
• DENIED_DIRS: Semicolon-separated list of denied directories
• RECURSIVE: When set to "true", all subdirectories of allowed directories are also allowed

Existing command-line argument functionality would be maintained for backward compatibility.

Benefits

1. Improved Readability: Complex directory configurations can be expressed more cleanly
2. Easier Management: Multiple directories can be configured in a single line with semicolon separators
3. Reusability: Environment variables can be easily reused in scripts or Docker configurations
4. Backward Compatibility: Existing command-line argument approach continues to work

Implementation Example

Here's an example of changes to the index.ts file:

// Load settings from environment variables
function parseDirectories(envVarValue: string | undefined): string[] {
  if (!envVarValue) return [];
  return envVarValue
    .split(';')
    .map((dir) => dir.trim())
    .filter(Boolean);
}

// Get settings from environment variables
const envAllowedDirs = parseDirectories(process.env.ALLOWED_DIRS);
const envAllowedReadOnlyDirs = parseDirectories(process.env.ALLOWED_READONLY_DIRS);
const envDeniedDirs = parseDirectories(process.env.DENIED_DIRS);
const envRecursive = process.env.RECURSIVE === 'true';

// Parse command-line arguments
const args = process.argv.slice(2);
if (args.length === 0 && envAllowedDirs.length === 0 && envAllowedReadOnlyDirs.length === 0) {
  console.error(
    'Usage: mcp-server-filesystem [options] <allowed_directory> [additional_directories...]'
  );
  // ... existing help text ...
  console.error('');
  console.error('Configuration via environment variables:');
  console.error('  ALLOWED_DIRS: Semicolon-separated list of allowed directories');
  console.error(
    '  ALLOWED_READONLY_DIRS: Semicolon-separated list of read-only allowed directories'
  );
  console.error('  DENIED_DIRS: Semicolon-separated list of denied directories');
  console.error(
    '  RECURSIVE: When set to "true", all subdirectories of allowed directories are also allowed'
  );
  console.error('  Example:');
  console.error(
    '    ALLOWED_DIRS="/home/user;/home/user/projects" DENIED_DIRS="/home/user/.ssh;/home/user/.config" RECURSIVE="true" mcp-server-filesystem'
  );
  process.exit(1);
}

Usage Example

Example in mcp.json file:

{
  "mcpServers": {
    "filesystem": {
      "command": "node",
      "args": ["/path/to/filesystem/dist/index.js"],
      "env": {
        "ALLOWED_DIRS": "/home/user",
        "ALLOWED_READONLY_DIRS": "/home/user/Documents;/home/user/Library/Mobile Documents/com~apple~CloudDocs",
        "DENIED_DIRS": "/home/user/.ssh;/home/user/.config;/home/user/.local;/home/user/.cache;/home/user/.npm;/home/user/.yarn;/home/user/.pnpm;/home/user/.cargo;/Volumes/BackUp",
        "RECURSIVE": "true"
      }
    }
  }
}

I believe this enhancement will significantly improve the usability of the MCP Filesystem Server.

Start in index.ts and inspect the existing command-line argument parsing and usage output. Add support for ALLOWED_DIRS, ALLOWED_READONLY_DIRS, DENIED_DIRS, and RECURSIVE while preserving the current CLI behavior. Done means the environment variables configure directories as described, including semicolon-separated values and recursive mode.