Documentation

Web Direct POS Print

Print receipts instantly from any web POS — no dialog, no delay. A desktop bridge app that connects your web-based POS directly to a local printer (dot matrix LPT or thermal POS) over a local HTTP server at http://localhost:3535.

Your web app sends a single fetch POST and the receipt prints immediately — no browser print dialog, no driver pop-ups. The app minimizes to the system tray when closed — the HTTP server keeps running in the background.

Contents

Features
GET /status
GET /printers
POST /print — Field Reference
Integration Examples

Features

Local HTTP server on port 3535 with open CORS (callable from any origin)
Raw printing — ESC/P and ESC/POS commands are sent as-is to the printer
Printer support:
- macOS/Linux: CUPS (lp -o raw), or direct device path (/dev/usb/lp0)
- Windows: RAW spooler (winspool) for printers with a driver, or direct write to LPT1/COM3 for parallel dot matrix without a driver
ESC/POS helpers: paper cut (cut), cash drawer (drawer), form feed
System tray icon — close button hides to tray, HTTP server keeps running
UI for selecting the default printer, test print, and real-time job log
Browser support: Chrome, Firefox, Edge, and other Chromium-based browsers — not Safari

Menu bar interface — endpoint, printer selector, and live print log

API Reference

GET /status

Check if the app is running.

{
  "status": "ok",
  "app": "printer-bridge",
  "version": "0.1.0"
}

GET /printers

List available printers and the current default.

{
  "printers": ["EPSON_LX310", "POS58"],
  "default": "POS58"
}

POST /print — Field Reference

Send a JSON body with Content-Type: application/json. A non-JSON body (text/plain / application/octet-stream) is sent as-is to the default printer.

Field	Type	Description
`printer`	string	Printer name. Omit to use the default printer.
`data`	string	Text to print (alias: `text`).
`base64`	string	Raw bytes encoded as base64 (logos, barcodes, binary ESC/POS commands).
`feed`	number	Number of extra line feeds appended at the end.
`cut`	boolean	Cut paper (ESC/POS `GS V`) — for thermal POS printers.
`drawer`	boolean	Open cash drawer (ESC/POS `ESC p`).
`formfeed`	boolean	Send form feed `0x0C` — for dot matrix continuous form.
`qr`	string	Text/URL printed as an ESC/POS QR code (center-aligned).
`qr_size`	number	QR module size 1–16 (default `6`, ≈3 cm on 80 mm paper).
`logo`	string	PNG/JPEG image URL — downloaded and printed as a bitmap at the top.
`logo_width`	number	Logo print width in pixels (default `300`, max `576` for 80 mm paper).
`logo_text`	string	Text to the right of the logo (use `\n` for line breaks). When set, the logo is scaled small and layout becomes `[logo │ text]`.
`logo_size`	number	Logo box size when displayed beside text, in pixels (default `88`).

Note: HTTPS pages may call http://localhost — browsers treat localhost as a secure context, so there is no mixed-content block. Safari is not supported — it blocks these local requests. Use Chrome, Firefox, Edge, or another Chromium-based browser.

Integration Examples

// Minimal — print to default printer, cut & open drawer

await fetch("http://localhost:3535/print", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    data: "receipt text...\n",
    cut: true,
    drawer: true,
  }),
});

// Full receipt — logo, QR code, cut & drawer

await fetch("http://localhost:3535/print", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    logo: "https://example.com/logo.png",
    logo_text: "Example Company\nExample Subtitle",
    logo_size: 88,
    data: "================================\n"
        + "   EXAMPLE COMPANY\n"
        + "   123 Example Street\n"
        + "================================\n"
        + "No  : INV/2026/06/00001\n"
        + "Date: 15-06-2026  10:32:45\n"
        + "--------------------------------\n"
        + "Name   : JOHN DOE\n"
        + "--------------------------------\n"
        + "Service Charge:    45,000\n"
        + "TOTAL DUE     :    47,500\n"
        + "================================\n"
        + "  Thank you for your payment.\n",
    qr: "https://example.com",
    qr_size: 6,
    feed: 3,
    cut: true,
    drawer: true,
  }),
});

// Thermal POS — feed before cut so last line isn't cut off

await fetch("http://localhost:3535/print", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    data: "receipt text...\n",
    feed: 4,
    cut: true,
  }),
});

// Dot matrix LPT — feed to tear bar (calibrate once per printer)

LX-310 is typically 5–7 lines from print head to tear bar.

await fetch("http://localhost:3535/print", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    printer: "LPT1",
    data: "receipt text...\n",
    feed: 6,
  }),
});

// Dot matrix — continuous form with fixed page length

await fetch("http://localhost:3535/print", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    printer: "LPT1",
    data: "receipt text...",
    formfeed: true,
  }),
});

Questions? Contact the developer at [email protected]