Do you ever look at a Modbus hex string and wonder what it really means?
Are you trying to check if your PLC or SCADA system is sending the right values?
Or do you just need to quickly create a Modbus command to test a device?
This Free Online Modbus Decoder and Encoder is built to make those tasks easy. It helps you decode and generate Modbus frames without installing any software. Everything runs directly in your browser.
The tool works with both Modbus RTU (serial) and Modbus TCP (Ethernet), so you can use it for most industrial systems.
Table of Contents
Why This Modbus Tool Is Useful
Working with Modbus can take a lot of time.
Manually checking CRC values, converting hex to floats, or fixing byte-order problems can slow you down.
This tool removes that hassle by doing the hard work for you.
1. Works With Both Modbus RTU and TCP
You don’t need separate tools anymore.
- Modbus RTU
- Checks the CRC automatically
- Confirms if the frame is valid
- Modbus TCP
- Decodes the MBAP header
- Shows transaction ID, length, and unit ID
The tool automatically recognizes whether the frame is RTU or TCP.
2. Easy Data Format Display
Modbus data is not always simple. The same registers can represent integers, floats, or other formats depending on the device.
This tool lets you view data in the format you need:
- 16-bit, 32-bit, and 64-bit integers (signed and unsigned)
- 32-bit float and 64-bit double values
- Big-endian and little-endian byte order
- Byte-swapped formats for devices that use non-standard layouts
- Raw views like hexadecimal, binary, and ASCII-hex
This makes it much easier to understand sensor values, counters, and process data.
3. Request and Response Decoding Together
Many tools only decode one frame at a time. This one lets you enter both the request and the response.
Why this helps:
- The tool knows which registers were requested
- It shows the correct register addresses in the response
- Coil and discrete input bits are displayed correctly without confusion
This is very helpful when debugging read requests and responses.
4. Built-In Modbus Frame Generator
You can also create Modbus frames, not just decode them.
The encoder lets you:
- Choose RTU or TCP
- Select a function code
- Enter addresses, quantities, or values
- Automatically generate a valid Modbus frame
The tool checks your inputs so you don’t create invalid frames. CRC (RTU) and headers (TCP) are added automatically.
Supported Modbus Function Codes
The tool supports the most commonly used Modbus functions, including:
Coil and Discrete Input Functions
- Read Coils (01)
- Read Discrete Inputs (02)
- Write Single Coil (05)
- Write Multiple Coils (15)
Register Functions
- Read Holding Registers (03)
- Read Input Registers (04)
- Write Single Register (06)
- Write Multiple Registers (16)
- Read/Write Multiple Registers (23)
Diagnostic and Information Functions
- Read Exception Status (07)
- Diagnostics (08)
- Get Communication Event Counter (11)
- Get Communication Event Log (12)
- Report Slave ID (17)
- Read FIFO Queue (24)
These cover almost all real-world Modbus use cases.
How to Debug a Modbus Problem in 3 Simple Steps
Step 1: Capture the Frame
Use a serial sniffer, protocol analyzer, or Wireshark to capture the Modbus hex data.
Example:01 03 04 42 F6 00 00 6C A5
Step 2: Paste and Decode
Paste the frame into the decoder.
The tool will:
- Detect Modbus RTU
- Show Slave ID 1
- Identify Function Code 03 (Read Holding Registers)
- Confirm the CRC is valid
Step 3: View the Data
Choose 32-bit Float (Big-endian) as the display format.
The tool shows that 42 F6 00 00 equals 123.0.
Now you know exactly what value the device is sending.
Common Modbus Issues and Fixes
“My values look wrong or too large”
This usually means the wrong data format is selected.
Try switching between integer, float, or byte-swapped formats until the value makes sense.
“The CRC is invalid”
This often happens because of:
- Electrical noise
- An incomplete frame capture
The tool shows whether the CRC matches, helping you confirm data integrity.
“The register number is off by one”
Some documentation uses register numbers like 40001, but Modbus uses zero-based addresses internally.
For example:
- Register 40001 → Address 0
This is normal and expected behavior.
Work Faster With Modbus
Stop wasting time converting hex values by hand or guessing data formats.
This Free Online Modbus Decoder and Encoder helps you:
- Debug faster
- Understand Modbus data clearly
- Test PLCs and devices easily
It’s fast, accurate, and completely free — a practical tool for everyday SCADA and automation work.
Frequently Asked Questions (FAQ)
Is this Modbus decoder really free?
Yes. The tool is completely free to use. There are no limits, no sign-ups, and no paid features. You can decode and encode as many Modbus frames as you want.
Do I need to install anything?
No. The Modbus decoder and encoder runs entirely in your web browser. You don’t need to download or install any software.
Does it support both Modbus RTU and Modbus TCP?
Yes. The tool supports both Modbus RTU (serial communication) and Modbus TCP (Ethernet). It automatically detects the protocol based on the frame structure.
Can I use this tool to generate Modbus commands?
Yes. You can create Modbus request frames using the encoder. Just select the function code, enter the address and values, and the tool generates a valid Modbus frame for RTU or TCP.
Can I decode floating-point and 32-bit or 64-bit values?
Yes. The tool supports:
16-bit, 32-bit, and 64-bit integers (signed and unsigned)
32-bit float and 64-bit double values
Multiple byte orders, including byte-swapped formats
This helps you correctly interpret sensor readings and process values.
Conclusion
Working with Modbus does not have to be slow or complicated.
This Free Online Modbus Decoder and Encoder gives you an easy way to understand Modbus RTU and TCP frames without installing any software.
You can quickly decode hex data, check CRC values, view register data in the correct format, and generate valid Modbus commands when needed. Whether you are troubleshooting a PLC, checking sensor values, or learning how Modbus works, the tool helps you get clear answers fast.
Everything runs directly in your browser, your data stays private, and the tool is free to use. It is a practical, time-saving utility for engineers, technicians, and students who work with Modbus every day.
If you regularly deal with Modbus communication, this tool can make your work simpler, faster, and more reliable.
Try the Modbus Decoder
You can start using the Modbus Decoder right away. No setup is required.
Decode Frame
Request frame (optional):
Response frame:
Starting address (optional, ignored when Request frame is provided):
Display Format:
Encode Frame
Support & Feedback
Having trouble decoding a frame, or noticed unexpected output?
We’re here to help!
When contacting support, please include:
- Decoder tool name (e.g., DNP3 Decoder, Modbus Decoder, IEC-101 Decoder, IEC-104 Decoder…)
- Description of the issue
- Frame/hex example or error message you encountered
(copy the frame you tested and any error code shown)
This information helps us quickly identify the issue and improve the tool for everyone.
Contact Support: SCADA Protocols Support Page