Filesystem MCP Server

Secure filesystem MCP server for reading, writing, searching, diffing, and patching files.

Table of Contents

• Overview
• Key Features
• Quick Start — Docker · CLI Usage
• Client Configuration
• Use Cases
• Architecture
• MCP Surface — Tools · Resources · Prompts
• MCP Capabilities — Tool Annotations · Structured Output
• Configuration — HTTP & Auth · File Size Limits · Access Control · Output & Inline Limits · Tasks · Logging & Diagnostics · Performance
• HTTP Endpoints
• Security
• Development
• Troubleshooting
• Credits
• Contributing and License

Overview

A secure, production-ready Model Context Protocol server that gives AI assistants controlled access to the local filesystem. All operations are sandboxed to explicitly allowed directories with path traversal prevention, sensitive file blocking, and optional Bearer token authentication.

Supports stdio (default) and Node Streamable HTTP transport. HTTP sessions are implemented with isolated per-session server state. The HTTP transport is stateful by default and currently non-resumable; it does not persist an event store for Last-Event-ID replay.

Key Features

• 18 filesystem tools — read, write, search, diff, patch, hash, and bulk operations with structured output schemas
• Security-first — path validation, symlink escape prevention, sensitive file denylist, localhost-only CORS, Host header validation for loopback HTTP binds, optional API key auth
• Dual transport — stdio for local use, Node Streamable HTTP for networked/multi-session deployments
• Structured output — all tools return typed outputSchema / structuredContent for reliable LLM parsing
• Self-documenting — 6 built-in resources (internal://instructions, internal://tool-catalog, etc.) and 4 built-in prompts (get-help, compare-files, analyze-path, get-tool-help)

Requirements

• Node.js >= 24

Quick Start

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

Docker

docker run -i --rm -v /path/to/project:/workspace:ro ghcr.io/j0hanz/filesystem-mcp /workspace

Or using Docker Compose:

services:
  filesystem-mcp:
    build: .
    stdin_open: true
    volumes:
      - ./:/projects/workspace:ro
    command: ['/projects/workspace']

CLI Usage

filesystem-mcp [options] [allowedDirs...]

Arguments:
  allowedDirs              Directories the server can access

Options:
  --allow-cwd              Allow the current working directory as an additional root
  --port <number>          Enable HTTP transport on the given port
  -v, --version            Display server version
  -h, --help               Display help

Examples:
  $ npx @j0hanz/filesystem-mcp@latest /path/to/project
  $ npx @j0hanz/filesystem-mcp@latest --allow-cwd
  $ npx @j0hanz/filesystem-mcp@latest --port 3000 /path/to/project

Client Configuration

{
  "servers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

code --add-mcp '{"name":"filesystem","command":"npx","args":["-y","@j0hanz/filesystem-mcp@latest"]}'

{
  "servers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

code-insiders --add-mcp '{"name":"filesystem","command":"npx","args":["-y","@j0hanz/filesystem-mcp@latest"]}'

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "servers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

extensions:
  filesystem:
    name: Filesystem MCP
    cmd: npx
    args:
      - -y
      - '@j0hanz/filesystem-mcp@latest'
    enabled: true
    type: stdio

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

claude mcp add filesystem-mcp -- npx -y @j0hanz/filesystem-mcp@latest

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

amp mcp add filesystem-mcp -- npx -y @j0hanz/filesystem-mcp@latest

{
  "amp.mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

codex mcp add filesystem -- npx -y @j0hanz/filesystem-mcp@latest

[mcp_servers.filesystem]
command = "npx"
args = ["-y", "@j0hanz/filesystem-mcp@latest"]

{
  "mcpServers": {
    "filesystem": {
      "type": "local",
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"],
      "tools": ["*"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "context_servers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"],
      "env": {}
    }
  }
}

{
  "augment.advanced": {
    "mcpServers": [
      {
        "id": "filesystem",
        "command": "npx",
        "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
      }
    ]
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@j0hanz/filesystem-mcp@latest"]
    }
  }
}

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Use Cases

Explore and Understand a Codebase

Discover project structure and navigate unfamiliar repositories. Start with roots to see allowed directories, use tree for an overview, find to locate files by pattern, and read or read_many to inspect contents.

Relevant tools: roots, ls, find, tree, read, read_many, stat

Search Across Files

Locate specific code patterns, function definitions, or configuration values across a project. Use grep for content search with regex support and find for file name matching.

Relevant tools: grep, find

Edit and Refactor Code

Make precise, targeted edits to source files. Use edit for surgical replacements with dry-run preview, or search_and_replace for bulk changes across multiple files matching a glob pattern.

Relevant tools: edit, search_and_replace, write

Diff and Patch Workflow

Compare file versions and apply patches. Generate a unified diff with diff_files, preview with apply_patch(dryRun: true), then apply. Supports both single-file and multi-file patches (best-effort per file with per-file results[]).

Relevant tools: diff_files, apply_patch

File Management

Create directories, move/rename files, delete files, and verify file integrity via SHA-256 hashing.

Relevant tools: mkdir, mv, rm, calculate_hash, write

Architecture

[MCP Client]
    |
    | Transport: stdio (default) or Node Streamable HTTP (--port)
    v
[MCP Server: filesystem-mcp]
    | Entry: src/index.ts -> src/server/bootstrap.ts
    |
    +-- initialize / initialized
    |
    +-- tools/call ──────────────────────────────────────────
    |   +-- [roots]             — List allowed workspace roots
    |   +-- [ls]                — List directory contents
    |   +-- [find]              — Find files by glob
    |   +-- [tree]              — Render directory tree
    |   +-- [read]              — Read file contents
    |   +-- [read_many]         — Read multiple files
    |   +-- [stat]              — Get file metadata
    |   +-- [stat_many]         — Get multiple file metadata
    |   +-- [grep]              — Search file contents
    |   +-- [mkdir]             — Create directory
    |   +-- [write]             — Write file
    |   +-- [edit]              — Edit file (string replacements)
    |   +-- [mv]                — Move/rename file
    |   +-- [rm]                — Delete file
    |   +-- [calculate_hash]    — SHA-256 hash
    |   +-- [diff_files]        — Unified diff
    |   +-- [apply_patch]       — Apply unified patch
    |   +-- [search_and_replace]— Bulk search & replace
    |
    +-- resources/read ──────────────────────────────────────
    |   +-- internal://instructions
    |   +-- internal://tool-catalog
    |   +-- internal://workflows
    |   +-- internal://tool-info/{name}
    |   +-- filesystem-mcp://result/{id}
    |   +-- filesystem-mcp://metrics
    |
    +-- prompts/get ─────────────────────────────────────────
    |   +-- get-help (optional topic argument)
    |   +-- compare-files (original, modified)
    |   +-- analyze-path (path)
    |   +-- get-tool-help (name)
    |
    +-- Capabilities: logging, resources, tools, prompts, completions, tasks

Request Lifecycle

[Client] -- initialize {protocolVersion, capabilities} --> [Server]
[Server] -- {protocolVersion, capabilities, serverInfo} --> [Client]
[Client] -- notifications/initialized --> [Server]
[Client] -- tools/call {name, arguments} --> [Server]
[Server] -- validate(inputSchema) --> [Handler]
[Handler] -- {content: [{type, text}], structuredContent?, isError?} --> [Client]

MCP Surface

Tools

roots · ls · find · tree · read · read_many · stat · stat_many · grep · mkdir · write · edit · mv · rm · calculate_hash · diff_files · apply_patch · search_and_replace

roots

List allowed workspace roots. Call first — all other tools are scoped to these directories.

No parameters.

ls

List immediate directory contents: name, path, type, size, modified date.

find

Find files by glob pattern. Returns matching files with metadata.

tree

Render a directory tree with bounded recursion. Returns ASCII tree + structured JSON.

read

Read text file contents. Use head/tail to preview first/last N lines of large files.

read_many

Read multiple text files in one request.

stat

Get file/directory metadata: size, modified, permissions, mime, tokenEstimate.

stat_many

Get metadata for multiple files/directories in one request.

grep

Search file contents (grep-like). Returns matching lines with optional context.

mkdir

Create a new directory (recursive). Idempotent.

write

Write content to a file, overwriting all existing content. Creates parent directories if needed.

edit

Apply sequential literal string replacements (first occurrence per edit). Use dryRun to preview.

mv

Move or rename a file or directory.

rm

Permanently delete a file or directory. Irreversible.

calculate_hash

Calculate SHA-256 hash of a file or directory.

diff_files

Generate a unified diff between two files. Output feeds directly into apply_patch.

apply_patch

Apply a unified diff patch to one or more files. Single-file: throws on failure. Multi-file: best-effort per file with results[]. Workflow: diff_files -> apply_patch(dryRun) -> apply_patch.

search_and_replace

Bulk search-and-replace across files matching a glob. Replaces all occurrences per file. Always dryRun: true first.

Resources

Prompts

MCP Capabilities

Tool Annotations

Structured Output

All 18 tools define outputSchema (Zod -> JSON Schema) and return structuredContent alongside text content. Set FS_CONTEXT_STRIP_STRUCTURED=true to strip output schemas from tool definitions (reduces token usage for LLMs that don't use structured output).

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Configuration

HTTP & Auth

File Size Limits

Access Control

Output & Inline Limits

Tasks

Logging & Diagnostics

Performance

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HTTP Endpoints

When started with --port <number>, the server exposes a single MCP endpoint:

Required headers:

• mcp-protocol-version — use the negotiated MCP protocol version on post-initialize HTTP requests
• mcp-session-id — required for GET/DELETE (returned by POST on initialize)

Authentication: Requests to non-loopback HTTP binds require FILESYSTEM_MCP_API_KEY; clients must then send Authorization: Bearer <key>. Loopback-only binds may omit auth for local use. Uses SHA-256 timing-safe comparison.

CORS: Only localhost origins allowed (127.0.0.1, ::1, localhost).

Host validation: Loopback HTTP binds validate the Host header (localhost, 127.0.0.1, [::1]) to reduce DNS rebinding risk. Non-loopback binds still require FILESYSTEM_MCP_API_KEY.

Security

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Development

• dev — tsc --watch --preserveWatchOutput — Watch mode TypeScript compilation
• dev:run — node --env-file=.env --watch dist/index.js — Run server with auto-reload
• start — node dist/index.js — Run production server
• build — node scripts/tasks.mjs build — Clean build
• test — node scripts/tasks.mjs test — Build + run all tests
• test:fast — node --test --import tsx/esm src/__tests__/**/*.test.ts node-tests/**/*.test.ts — Run tests without build
• lint — eslint . — Lint source
• type-check — node scripts/tasks.mjs type-check — Type-check src + tests
• format — prettier --write . — Format code
• inspector — npm run build && npx -y @modelcontextprotocol/inspector node dist/index.js ${workspaceFolder} — Launch MCP Inspector

Build and Release

• CI: .github/workflows/release.yml — runs lint, type-check, test, build before tagging/publishing.
• Docker: Multi-stage build with node:24-alpine. Builder compiles TypeScript + native modules (re2); release stage runs as non-root mcp user.
• npm: npm run prepublishOnly runs lint + type-check + build.

Troubleshooting

• "No allowed directories" — Pass at least one directory argument or use --allow-cwd.
• Sensitive file blocked — Files matching the denylist (.env*, .git, SSH keys) are blocked by design. Check src/lib/constants.ts for the full list.
• Large result externalized — When tool output exceeds inline limits, it's cached as a resource at filesystem-mcp://result/{id}. Read the resource URI to get the full content.
• Stdio: logs on stdout — Keep logs on stderr only. The server uses console.error for diagnostics.
• HTTP 413 — Request body exceeds FS_CONTEXT_MAX_REQUEST_BYTES. Increase the limit or reduce payload size.
• HTTP 401 — FILESYSTEM_MCP_API_KEY is set but the request is missing or has an incorrect Authorization: Bearer header.

Credits

License

MIT License. See LICENSE for details.

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