Give your website
local machine power.

web2local is a tiny daemon that bridges websites to your local environment — safely. Your site can run commands, read files, and talk to hardware that a browser alone can never reach.

How it works

Browsers are sandboxed on purpose — a web page cannot touch your filesystem, run a process, or connect to a serial port without explicit permission. But some tools genuinely need local power: build scripts, hardware dashboards, developer utilities, media processors.

web2local runs a small HTTP server bound to 127.0.0.1 only (never reachable from the internet). Your website calls it with fetch(). The daemon checks who is asking, then acts accordingly.

The daemon answers only to requests whose Host header is 127.0.0.1 or localhost. This one check kills the most dangerous class of localhost attacks — DNS rebinding — where a malicious site manipulates DNS to make the browser treat evil.com as a local address.

Security model

Every request carries an Origin header — the site that made it. The daemon classifies that origin into one of three tiers:

What the graylist dialog shows you

When a graylist site sends a command, a window appears with:

• The exact requesting origin (the website's URL)
• The full command in a scrollable monospace box — no truncation
• A countdown timer (auto-deny at zero)
• Two buttons: Deny and Allow Execution

The command is displayed as an argument list — no shell expansion happens. What you see is exactly what will run. Scroll right if it is long; the dialog will not dismiss until you click a button.

What it does not protect against

Quick start

python3 daemon.py

# Whitelist (trust fully)
curl -s -X POST http://127.0.0.1:7878/config/whitelist \
  -H 'Content-Type: application/json' \
  -d '{"origin":"https://mysite.com"}'

# Graylist (ask before each command)
curl -s -X POST http://127.0.0.1:7878/config/graylist \
  -H 'Content-Type: application/json' \
  -d '{"origin":"https://other-site.com"}'

<script src="client.js"></script>

const w2l = new Web2Local();   // default port 7878

if (await w2l.isRunning()) {
  const r = await w2l.run("ls", ["-la", "/tmp"]);
  console.log(r.stdout);
  console.log("exit:", r.exit_code);
} else {
  console.warn("web2local daemon not running");
}

API reference

All endpoints are on http://127.0.0.1:7878.

Error responses

403  {"error": "origin not in whitelist or graylist"}
403  {"error": "command denied by user"}
403  {"error": "host must be 127.0.0.1 or localhost"}
400  {"error": "command must be a non-empty string"}
408  {"error": "command timed out (30 s limit)"}

Command rules

• command is the executable name — no shell, no &&, no pipes.
• args is a flat list of strings — each element is one argument.
• Commands time out after 30 seconds.
• The process inherits the daemon's environment and working directory.
• A bare python/python3 runs in your selected environment (pixi/conda/venv): set "python" in config.json, approve POST /env/select or POST /setup-env, or rely on auto-detection of a project-local .venv/.pixi or the daemon's active env. Pages propose environment changes; the daemon validates and persists them only after local approval.

Live demo

This page connects to your local daemon in real time.

Process manager

POST /run waits for the command to finish — fine for quick jobs, useless for daemons. POST /spawn starts a process and returns immediately with its PID. The daemon tracks every spawned PID, captures its output to a log file, and lets you stop it from this page.

Deployed scripts

Scripts delivered via POST /deploy are stored in ~/.config/web2local/agents/ under a filename prefixed with the first 8 chars of their SHA-256. Each entry records which site deployed it. Delete a script here to revoke it permanently.