Features

Serial, TCP/UDP and remote ports, debugged in one window.

Open up to 16 connections side by side, read the traffic as text or hex, build and replay frames, bridge a serial port onto the network, and share it with someone who is not in the room. Everyday debugging is free and needs no account.

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Windows, macOS and Linux Version 6.6.8

Serial Port Utility with a serial console and a TCP server open side by side
Two connections in one window: a device shell on a serial port, and a TCP server waiting beside it.
Connect

Five ways to reach a device, up to sixteen at a time.

Serial, TCP client and server, UDP client, server and multicast, plus a remote serial port over RFC 2217 — every mode opens in the same window, so a gateway and the port behind it are never two separate tools.

  • Up to 16 connections on screen, in four layouts
  • Custom baud rates beyond the presets
  • Data bits, parity, stop bits and flow control
  • TCP server (multi-client) and TCP client
  • UDP client, server and multicast (UDP group)
  • RFC 2217 client: open a port on a device server and set its baud rate, framing and control lines from here
Serial connection parameters TCP and UDP debugging RFC 2217 client
A remote serial port opened over RFC 2217, with the device output in the receive view
A port on a device server, opened over RFC 2217 and driven like a local one.
Inspect

Read the bytes the device actually sent.

Switch between text and hex, pick the encoding each connection speaks, and timestamp every line so a capture taken tonight still answers questions next week.

  • Switch between ASCII and Hex
  • Per-connection send and receive encodings: UTF-8, GBK, GB18030, Big5, Shift-JIS and more
  • Configurable time formats
  • Rotate logs by size or time
  • TX/RX and control-line lamps show the link is alive
Text, Hex and encodings Logs and long-running capture Indicator lamps and control lines
Modbus frames arriving over TCP, shown in Hex with a millisecond timestamp on every line
Hex view with Auto FL and Display Time switched on: every frame on its own line, stamped to the millisecond.
Compose

Build a frame once, then replay it.

Keep the frames you send often in a reusable list, let the checksum be appended for you, and hand Modbus RTU frames to the request builder instead of counting bytes by hand.

  • Modbus request builder in the Tools menu
  • CRC-8/16/32 family: MODBUS, USB, CCITT, XMODEM and more
  • Custom CRC parameters, fed straight into the send frame
  • Auto-append the checksum when sending
  • Loop send at a fixed interval, or line by line
  • Send history keeps earlier frames one click away, and follows your account to other computers

The request builder is in Free with a per-session allowance; Pro removes the limit.

Automatic send and command lists CRC and Modbus checks Script automation (Lua)
The Modbus request builder assembling an RTU frame
The request builder assembles the RTU frame and its CRC, ready to copy or drop into the send box.
Bridge

Turn this machine into a serial device server.

Link two connections and a program on the network reads and writes the local serial port directly, while both sides of the traffic stay on screen. A fast network feeding a slow port is throttled automatically, and whatever still has to be dropped is counted until you clear it.

  • Transparent forwarding, in one direction or both
  • RFC 2217 server: a remote machine sets baud rate, framing and control lines as if the port were local
  • Modbus gateway converts TCP frames to RTU, and serves masters on a shared RS-485 bus one at a time
  • Several clients handled exclusively, by broadcast, or in turn
  • An address allowlist keeps strangers off the port
  • Both directions recorded into one time-ordered capture file
RFC 2217 server
The bridge editor linking a serial connection to a TCP/UDP endpoint in both directions
The bridge editor: a serial port on one end, a TCP server on the other, and a list of who may connect.
Live Sync

Hand the port to whoever has to see it.

Four ways out of this machine, gathered under one status-bar entry. Every edition has all four; a paid licence adds monthly cloud traffic, not features.

  • RFC 2217 ServerOne dialog turns the open port into a listener on your own network, with an address allowlist and no grid slot spent
  • Live ConsoleWatch and drive this machine's ports from a signed-in browser, with remote send and port control granted separately
  • Live RelayOpen a port on another of your machines as if it were local — Modbus, X/YMODEM and firmware updates included
  • Live ShareMint a time-limited invite code for one port; the guest needs no account, subscription or install
  • The cloud paths only dial out from both ends, so NAT, no public address and a closed inbound port are not obstacles
  • The status bar says when a port is open to someone, and who is driving it right now
Choosing a remote access path Web remote debugging with Live Console Remote serial port with Live Relay Live Share (invite codes)
A Live Console device page: the port's live traffic and send bar on the left, the machine's ports and command history on the right
Live Console in a browser: the port's traffic, a send bar, and the other ports on that machine.
Deliver

Flash the firmware, save the session, carry on from another computer.

Push an image into a bootloader over the connection that is already open, keep the whole session in a project file, and let your settings follow your account.

X/YMODEM file transfer

XMODEM, XMODEM-CRC, XMODEM-1K, YMODEM and YMODEM-G, sending or receiving, over serial, TCP or an RFC 2217 remote port. Free carries a per-session allowance; Pro removes it.

File transfer (XMODEM / YMODEM)

Project files

Every connection and bridge in the session is saved as one .spu file and reopened on launch.

Settings and licence follow your account

Sign in on another computer and your settings and send history are there. A licence bound to the account activates that computer too, and is released when you sign out.

Licenses and your account
Free and Pro

Free is the whole debugger. Pro removes the limits.

Everything on this page ships in every edition, and local debugging never asks for an account.

Free

Everyday debugging, no account

  • Up to 16 connections at once: serial, TCP, UDP and RFC 2217 remote ports
  • Bridges, text and Hex views, checksums, automatic send and logs
  • Project files and settings sync
  • All four Live Sync paths, with a monthly cloud-traffic allowance
Pro

The same tools, without the allowances

  • Unlimited Modbus request builder
  • Unlimited X/YMODEM transfers, at any file size
  • Unlimited sequences, scripts, plots, decoding and replay
  • A far longer send history, local and synced
  • A larger monthly cloud-traffic allowance

Free has no time limit. Buy Pro when you need it; saved projects and logs are always kept.

Full Free vs Pro comparison View Pricing
Use Cases

Worked scenarios, from wiring to verification.

Each one names the topology, the settings that matter and the result you should be able to observe.

See all scenarios

Debug a serial port from anywhere on the Web

Use Live Console across locations and NAT without routing directly to the site or opening an inbound TCP port.

  1. On-site SPU
  2. Live Console
  3. Browser anywhere
Open scenario

Connect directly with RFC 2217

Reach a serial server directly over a LAN or VPN and control its serial parameters as well as its data.

  1. RFC 2217 Client
  2. Reachable LAN or VPN
  3. On-site serial server
Open scenario

Connect an isolated site outward

Use an outbound TCP client when the device site cannot accept inbound connections.

  1. Serial device
  2. SPU TCP Client
  3. Central server
Open scenario

Monitor a serial conversation inline

Capture both directions between an existing host and device without changing the protocol.

  1. Existing host
  2. SPU bridge
  3. Serial device
Open scenario

Forward serial telemetry over UDP

Turn NMEA or sensor messages into correctly framed UDP datagrams for a LAN collector.

  1. Sensor
  2. SPU framing
  3. UDP collector
Open scenario

Poll a Modbus RTU device reliably

Build a repeatable request, verify CRC and separate timeout from framing failures.

  1. SPU poll command
  2. RS-485 adapter
  3. Modbus device
Open scenario

Capture an intermittent fault overnight

Record timestamped traffic with bounded files and preserve a useful incident window.

  1. Serial link
  2. SPU logging
  3. Rotated evidence files
Open scenario

Update device firmware over serial

Send an image to a bootloader with YMODEM, locally or through a device server.

  1. Firmware image
  2. SPU YMODEM
  3. Device bootloader
Open scenario
Next Step

Try it against your own device.

Install the build for your system, then follow the scenario closest to the link you are debugging.

Get the Latest Build See all scenarios