Serial Peripheral Test

A free browser serial-port diagnostic. Confirms a receipt printer, cash drawer, or pole display is actually talking on its COM / USB-serial port using the Web Serial API. It checks that the port opens, the baud rate negotiates, and bytes are writable - and can optionally send an ESC/POS status query to see whether the device replies. Useful for isolating "is it the hardware or the POS app?" before you call the vendor.

Read the Serial Peripheral Test guide for help reading the verdict or fixing each failure mode.

Privacy: Web Serial only exposes the one port you explicitly pick in the browser's chooser. No port data leaves the workstation; the optional status query stays on the wire between this tab and the device. View source to verify.

Configuration

Baud rate

Send an ESC/POS status query (DLE EOT) and read any reply

Takes about 20 seconds. You choose the port in a browser chooser; nothing opens without your click. The optional status query writes 3 bytes (10 04 01) - a read-only ESC/POS "transmit status" request that does not print or kick a drawer. Uncheck it to verify writability only.

Status Check Step

Pending

Browser supports Web Serial

Feature-detecting navigator.serial in a secure context.

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Pending

Port opens and baud negotiates

Click below to open the browser's port picker, then choose your COM / USB-serial port.

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Pending

Port is writable (optional status reply)

Acquiring the write stream and, if enabled, sending an ESC/POS status query.

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