A command-line tool designed for serial port benchmarking, WebSocket bridging, and signal testing. It is particularly focused on testing loopback devices. I tested it with loopback devices based on the FT231X. Why such a device would be useful to anyone in 2026 is beyond me.
cargo build --release
Write 0xAA bytes continuously at maximum speed. Reports throughput every second. Ctrl+C exits immediately.
serial-tool write <port> <baud>
$ serial-tool write /dev/cu.usbserial-A 3000000
300000 bytes/sec written (300000 bytes in 1.00s)
300000 bytes/sec written (300000 bytes in 1.00s)
^C
Read from a serial port at maximum speed and print throughput every second.
serial-tool read <port> <baud>
$ serial-tool read /dev/cu.usbserial-B 3000000
300000 bytes/sec (300000 bytes in 1.00s)
Start a WebSocket server that bridges all connected clients to a serial port. Multiple clients share the same port: reads are broadcast to all clients, writes from any client go to the port.
serial-tool serve <port> <baud> <listen-addr>
$ serial-tool serve /dev/cu.usbserial-A 115200 0.0.0.0:9000
WebSocket server listening on ws://0.0.0.0:9000
Client connected: 192.168.1.5:52431
Connect to a remote WebSocket server and bridge it to a local serial port. Same bidirectional bridge as serve, but as a client.
serial-tool connect <port> <baud> <ws-url>
$ serial-tool connect /dev/cu.usbserial-B 3000000 ws://192.168.1.10:9000
Connected to ws://192.168.1.10:9000
Use serve on one machine and connect on another to link two serial ports over the network.
Continuously test RTS/CTS, DTR/DSR, and DTR/CD signal lines between two serial ports. Each test asserts that both the high and low transitions are observed on the other side. Runs in a loop until Ctrl+C.
serial-tool signals <portA> <portB>
$ serial-tool signals /dev/cu.usbserial-A /dev/cu.usbserial-B
Round 142: 6/6 PASS (total: 852 pass, 0 fail)
^C
Stopped after 142 rounds: 852 passed, 0 failed
Signals tested per round:
| Set on | Signal | Read on | Signal |
|---|---|---|---|
| A | RTS | B | CTS |
| B | RTS | A | CTS |
| A | DTR | B | DSR |
| B | DTR | A | DSR |
| A | DTR | B | CD |
| B | DTR | A | CD |
Exits with code 1 if any failures occurred.
A standalone HTML page for benchmarking serial throughput via WebSocket. Open it in a browser, point it at a running serve instance, and use the Read/Write benchmark buttons.
With standard 8N1 framing (10 bits per byte), the theoretical maximum is baud/10:
| Baud rate | Expected bytes/sec |
|---|---|
| 9600 | ~960 |
| 115200 | ~11,520 |
| 3000000 | ~300,000 |