Modbus frame decoder
Paste RTU, TCP or ASCII bytes and watch them decode as you type: function, addresses in every notation, CRC state and every plausible reading.
Nothing to install Decode a frame →Modbus CRC calculator
CRC-16/MODBUS over your bytes, live, beside the variants people mistake it for — and a builder that writes a valid request for you.
Nothing to install Calculate a CRC →Modbus RTU tester
Talk to a real slave through a USB-RS485 adapter: scan for addresses, hunt down the baud rate, read registers, write a coil.
Chrome or Edge, plus an adapter Read a slave →ESP32 serial monitor
A serial console that reads the boot log for you — resets, panics, brownouts and Wi-Fi failures each get a plain-English note.
Chrome or Edge, plus a USB cable Watch a board boot →ESP32 chip info
Chip, MAC, crystal and flash, then the partition table and app descriptor — so you can see which firmware is actually running.
Chrome or Edge, plus a USB cable Identify a board →ESP32 web flasher
Write a .bin to an ESP32, S2, S3, C3, C6 or ESP8266 from the browser. The file goes disk to chip; nothing is uploaded.
Chrome or Edge, plus a USB cable Flash a board →The tools stop when you close the tab. Synacl keeps reading.
Once the meter answers, the next question is always the same one: what was it doing at 3am? Synacl is the part after the bench — an ESP32 gateway polls the device, the readings land on a dashboard, and you get told when they move.
- Free tier, no card. One gateway, a handful of devices, real history.
- Your own hardware. Flash the open-source firmware onto any ESP32 you already own.
- Modbus RTU, TCP, MQTT and webhooks into one dashboard and one alerting rule set.
- Step-by-step in the guides, from a bare board to a live chart.
Questions about the tools
The three we get asked before anyone clicks anything.
Are these tools really free?
Yes. No account, no sign-up, no trial and no limit on how often you use them. They are the same code Synacl uses internally, published because the searches that bring people here — a CRC that will not match, a frame that will not decode, a board that will not boot — are the searches we were making ourselves. If you later want those readings kept, charted and alerted on, that is what Synacl is for.
What gets uploaded when I use them?
Nothing. The Modbus tools are plain JavaScript running in the page, and the ESP32 tools talk to the board over Web Serial, which is a direct connection from the browser to the USB port. Nothing you type or read leaves your browser. The only network request the tool makes is one anonymous ping (a GET to /tools/_/…, no cookies, no identifiers) when a decode or read succeeds, so we know the tool is used.
Which browsers do these tools work in?
The Modbus frame decoder and the CRC calculator work in any modern browser, phones included — they never touch hardware. The RTU tester, the serial monitor, the chip info reader and the flasher need the Web Serial API, which today means Chrome, Edge, Opera or another Chromium browser on a desktop. Firefox and Safari do not implement it, and neither do mobile browsers.