local-mcp

Version License Node Tests Dependencies

Zero-dependency MCP server for local file operations. 13 filesystem tools + 3 meta-tools for progressive discovery — no SDKs, no frameworks, no npm install needed.

MCP Protocol: 2024-11-05 · Transport: stdio + Streamable HTTP · Runtime: Node.js ≥ 22.0.0

Architecture

local-mcp.mjs       — 595 lines, 13 tools, entry point
lib/mcp-core.mjs    — 229 lines, stdio + HTTP transport, 9 MCP methods
lib/config.mjs      —  31 lines, MCP_WORKSPACE/DATA env config with validation

Total: ~855 lines, zero runtime dependencies.

Tools

Filesystem Tools (13)

Tool	Description	Annotation
`read`	Read file with line numbers, optional `head`/`tail` truncation	`readOnlyHint`
`search`	File search by name (glob) then content (grep)	`readOnlyHint`
`ls`	Compact directory listing with lazy stat	`readOnlyHint`
`exec`	Streaming command execution with stdin support and timeout	`destructiveHint`
`diff`	Diff two files or text strings (Myers O(ND))	`readOnlyHint`
`copy`	Copy file or directory	`destructiveHint`
`move`	Move or rename file/directory	`destructiveHint`
`batch`	Run multiple ops sequentially; atomic rollback, `$prev` refs	`destructiveHint`
`file`	Unified: read, write, edit, append, delete, info, mkdir, move	—
`block`	Read/replace/insert/delete code blocks by range or function name	—
`bookmark`	Persistent path aliases (add/get/list/delete)	—
`grep`	Compact `file:line:content` format with adaptive concurrency	`readOnlyHint`
`watch`	Watch file/directory for changes; max 20 concurrent watchers	—

Meta-Tools (3) — Progressive Discovery

Tool	Description
`search_tools`	Search available tools by keyword — saves ~90% tokens vs listing all
`describe_tool`	Get full input schema for a specific tool (loaded on demand)
`call_tool`	Execute any tool by name with arguments

Instead of sending all 13 tool schemas (~3,000 tokens) in every request, progressive discovery with these 3 meta-tools reduces it to ~50 tokens — ~90% token savings.

Performance Optimizations (v1.1.1)

#	Optimization	Impact
A	Stream head/tail read	`streamHead()` avoids reading entire files. 500MB logs: 3s → 5ms, memory: 500MB → few KB
B	Lazy stat in ls	Only calls `statSync` when `sort=size`. 1000-file dir: 50ms → 2ms
C	Adaptive grep concurrency	`os.availableParallelism()` (max 16, min 4) instead of hardcoded 16 workers
D	LRU cache eviction	Map insertion-order LRU — hot small files no longer evicted by cold large files
E	Grep byte protection	`MAX_GREP_TOTAL_MB=100` + `MAX_GREP_FILES=1000` guards prevent OOM
F	Progress notification	`_meta.progressToken` passthrough for MCP 2025 spec (TODO: events for long exec)

Additional Optimizations

Area	Detail
Read cache	Size-aware eviction (max 50 items, 10 MB) + 5s TTL
Myers diff	O(ND) algorithm, used by `edit`, `block`, and `diff`
Search scoring	Name-match first (no I/O), then stat only top 50 candidates
Output format	`grep`: `file:line:content`, `ls`: compact columns, `read`: line numbers + truncation hint
Protocol	O(1) Map dispatch, sync handler short-circuit

Getting Started

# Zero install — no dependencies
node local-mcp.mjs

# With configuration
MCP_WORKSPACE=D:/projects node local-mcp.mjs

stdio mode (default)

{
  "mcpServers": {
    "local-mcp": {
      "command": "node",
      "args": ["D:/path/to/local-mcp.mjs"],
      "env": {
        "MCP_WORKSPACE": "D:/projects"
      }
    }
  }
}

HTTP mode

node local-mcp.mjs --http
node local-mcp.mjs --http --port 3456

Supports JSON-RPC 2.0 POST, SSE streaming (Accept: text/event-stream), CORS, and GET /tools.

CLI flags

node local-mcp.mjs --help          # Show usage + env vars
node local-mcp.mjs --list-tools    # Print available tools and exit
node local-mcp.mjs --http          # Start HTTP mode
node local-mcp.mjs --http --port 3456

Configuration

Variable	Default	Description
`MCP_WORKSPACE`	`process.cwd()`	Working directory root (security boundary)
`MCP_DATA`	`{WORKSPACE}/.mcp-data`	Data directory (bookmarks, temp files)
`MCP_DIR`	`{WORKSPACE}`	Default directory for tree/ls commands
`MCP_PORT`	`3100`	HTTP server port (when using `--http`)
`MCP_READONLY`	`false`	Set to `true` to block all write operations
`MCP_EXCLUDE`	—	Comma-separated extra dirs to exclude from search

Security

All file operations restricted to MCP_WORKSPACE and subdirectories
Prototype-safe bookmark keys (blocks __proto__/constructor/prototype injection)
Atomic writes (temp + rename) prevent partial file writes
Binary file detection prevents reading non-text files
.gitignore and common exclude dirs (node_modules, .git, etc.) respected

Dependencies

Zero runtime dependencies. Uses only Node.js built-ins:

Module	Purpose
`fs`	File system + `glob` (Node 22)
`child_process`	Streaming shell execution
`http`	HTTP transport (no Express needed)
`path`	Path resolution
`os`	`availableParallelism()` for adaptive concurrency
`readline`	Streaming line-by-line processing

Changelog

v1.1.1 — Performance Optimizations

A. Stream head/tail read: 500MB logs 3s → 5ms
B. Lazy stat in ls: 1000-file dir 50ms → 2ms
C. Adaptive grep concurrency with availableParallelism()
D. LRU cache eviction via Map insertion order
E. Grep byte protection (100MB / 1000 files)
F. Progress notification passthrough for MCP 2025 spec
Fix: streamHead scope bug — done defined outside Promise callback

v1.1.0

13 filesystem tools + 3 meta-tools for progressive discovery
stdio + Streamable HTTP transport
Myers diff engine, read cache, streaming exec
Environment-based configuration with validation

Development

# Run tests
node --test test/*.test.mjs

# Adding a tool
# 1. Define schema + handler in local-mcp.mjs
# 2. Register with server.tool()
# 3. Add tests

Contributing

Maintain zero-dependency constraint
Add tests for new functionality
Update the Optimizations table for performance changes

License

MIT

local-mcp

local-mcp

Architecture

Tools

Filesystem Tools (13)

Meta-Tools (3) — Progressive Discovery

Performance Optimizations (v1.1.1)

Additional Optimizations

Getting Started

stdio mode (default)

HTTP mode

CLI flags

Configuration

Security

Dependencies

Changelog

v1.1.1 — Performance Optimizations

v1.1.0

Development

Contributing

License

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