auto-script-mcp

Self-generating, zero-token script registry and execution middleware for AI coding agents.

When AI coding agents (Cline, Roo Code, Cursor, Continue) do multi-step file manipulation, data processing, or batch operations, they burn tokens and latency doing work a local script could do in one shot. auto-script-mcp is a Model Context Protocol server that acts as a deterministic execution layer:

• Every saved script is exposed to the agent as a native MCP tool — script_<name> — with a real JSON Schema for its arguments.

• When no existing script fits a repetitive task, the agent writes one, and persists it with the built-in save_script tool. The new tool is mounted live (notifications/tools/list_changed) — no server restart, and it survives into every future session.

• Execution happens in a local subprocess (Node.js / TypeScript / Python). The agent pays tokens for one tool call instead of the whole operation.

┌────────────────────────────────┐
│  Client AI Agent (VS Code)     │
│ (Cline, Roo, Cursor, Continue) │
└───────────────┬────────────────┘
                │ JSON-RPC over stdio
                ▼
┌──────────────────────────────────────────────────────────┐
│                   auto-script-mcp Server                 │
│  Dynamic Tool Registry          Built-in MCP Tools       │
│   └─ script_<script_name>        ├─ save_script          │
│                                  ├─ list_scripts         │
│                                  └─ delete_script        │
└────────┬───────────────────────────────┬─────────────────┘
         ▼                               ▼
  Exec Subprocess                 Storage Layer
  (Node.js / Python,              - SQLite index (index.db)
   timeout + truncation)          - Local `.scripts/` files

Quick start

npm install -g auto-script-mcp   # or run from a clone: npm install && npm run build

Wire it into your agent

Cline / Roo Code (mcpServers in settings):

{
  "mcpServers": {
    "auto-script": {
      "command": "node",
      "args": ["/path/to/auto-script-mcp/dist/index.js"],
      "env": {}
    }
  }
}

Cursor (.cursor/mcp.json) and Continue use the same mcpServers shape.

On connect, the server also serves its playbook as server instructions and as the auto-script-instructions prompt:

Always review registered tools before executing multi-file operations. If no script matches the current task, create a reusable script, test it locally, and persist it via save_script.

Related MCP server: TokenLighten

How it works

1. You ask for a repetitive or bulk task in VS Code.

2. The agent checks its tools — including every dynamic script_* tool.

3. Match found → agent calls script_<name>(args); the server runs the subprocess and returns { success, stdout, stderr, duration_ms }. Tokens saved.

4. No match → agent writes a script, verifies it locally, calls save_script(...). The server syntax-checks it (dry-run), writes it to disk, indexes it in SQLite, emits tools/list_changed, and the new tool is available immediately — and on every future launch.

Tools

Built-in

Dynamic — script_<name>

One per saved script. Accepts exactly the arguments in that script's input_schema and returns:

{ "success": true, "stdout": "...", "stderr": "", "duration_ms": 42, "exit_code": 0 }

The script contract

Scripts receive their arguments three ways — use whichever is natural:

1. argv[2] (JS/TS) / sys.argv[1] (Python) — a JSON string of the args object

2. stdin — the same JSON string

3. SCRIPT_ARGS_JSON environment variable

Print results to stdout; exit 0 on success, non-zero on failure. Examples in examples/ (batch_json_transform.js, sync_db_schema.py).

Storage

.scripts/                                  # project scope: <cwd>/.scripts/
├── index.db                               # SQLite metadata store
└── src/
    ├── batch_json_transform.js
    ├── sync_db_schema.py
    └── extract_tailwind_classes.ts

~/.config/auto-script-mcp/scripts/         # global scope, same layout
├── index.db
└── src/…

CREATE TABLE IF NOT EXISTS scripts (
  id TEXT PRIMARY KEY,
  name TEXT UNIQUE NOT NULL,
  description TEXT NOT NULL,
  language TEXT NOT NULL,
  input_schema TEXT NOT NULL,
  file_path TEXT NOT NULL,
  scope TEXT NOT NULL,
  created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
  updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

Project scope wins on a name collision. On boot the server scans both stores and mounts every script it finds.

Safety & guardrails

• Execution timeout — subprocesses are killed after 30s by default (--timeout-ms flag or AUTO_SCRIPT_TIMEOUT_MS env to change; SIGTERM, then SIGKILL).

• Path sanitization — script names must match ^[a-z0-9_]+$; no traversal, no separators.

• Output truncation — stdout/stderr returned to the agent are capped at 8 KB so a chatty script can't blow the context window it exists to protect. Capture is also hard-capped in memory.

• Dry-run validation — save_script parses/checks syntax (node --check, TypeScript compiler diagnostics, py_compile) before anything is written to disk. Invalid code never becomes a tool.

• Scripts run with your user's permissions, in the project cwd — same trust model as the agent's own terminal. Only save scripts you'd run yourself.

Server options

auto-script-mcp [--project-dir <path>] [--global-dir <path>] [--timeout-ms <n>]
# Env equivalents: AUTO_SCRIPT_PROJECT_DIR, AUTO_SCRIPT_GLOBAL_DIR,
#                  AUTO_SCRIPT_TIMEOUT_MS, PYTHON_BIN

Development

npm install
npm run build
npm test        # end-to-end: real MCP client ↔ server — save, mount, run (JS/TS/Python), persist, timeout, truncation, delete

Roadmap

• HTTP transport (stdio today)

• Per-script permission prompts / allowlist for destructive scripts

• Script versioning + usage stats (which scripts actually save the most calls)

• Import/export packs of scripts between machines

License

MIT © Andrew Edouard