CRC Patch Finder
Text is converted to UTF-8 bytes.— standard check string
Result
CRC Patch Finder
CRC-16 / MODBUS · Input data: 9 bytes inherited · Uses the calculator's algorithm and data
About the CRC Patch Finder
The patch finder searches for a two-byte value that, when inserted at the end of your data (or at a chosen offset), makes the CRC of the patched data equal a target value you specify. It brute-forces all 65,536 two-byte combinations against the algorithm and input data currently configured in the calculator above.
This is useful for CRC-forcing scenarios such as reverse engineering firmware update mechanisms, crafting test vectors for a checksum-validated protocol, or verifying that a file format's integrity check can be produced deliberately. Change the algorithm or input data in the calculator to search a different CRC model.
Supported CRC parameters
Custom CRC calculations can be configured using width, polynomial, initial value, input reflection, output reflection, and final XOR value. These parameters allow the calculator to reproduce many standard and proprietary CRC implementations used in embedded systems, serial communication, industrial protocols, file formats, and network applications.
- Width
- Defines the CRC register size, such as 8, 16, or 32 bits.
- Polynomial
- Specifies the generator polynomial used by the CRC algorithm.
- Initial value
- Sets the value loaded into the CRC register before processing data.
- RefIn and RefOut
- Control whether input bytes and the final CRC result are reflected.
- Final XOR value
- Applies a final XOR operation to the CRC register before displaying the checksum.
CRC-8, CRC-16, and CRC-32
CRC-8 produces an 8-bit checksum and is commonly used in compact embedded and sensor protocols. CRC-16 produces a 16-bit checksum and is widely used by protocols such as Modbus, XMODEM, and CCITT-based communication systems. CRC-32 produces a 32-bit checksum and provides stronger error detection for larger files, archives, Ethernet frames, and storage formats.
CRC lookup table and source code generator
A CRC lookup table replaces repeated bit-by-bit polynomial operations with precomputed values. This can significantly improve checksum performance in firmware, embedded software, and high-throughput applications. The generated table and function code can be copied directly into C, Python, or JavaScript projects and adapted as needed.
Frequently asked questions
What is a CRC checksum?
A cyclic redundancy check, or CRC, is an error-detection method used to identify accidental changes in transmitted or stored data. The sender calculates a CRC value, and the receiver calculates it again to verify that the data has not been corrupted.
Which CRC algorithm should I use?
Use the algorithm required by your protocol or file format. For example, Modbus commonly uses CRC-16/MODBUS, while other systems may require CCITT-FALSE, XMODEM, KERMIT, CRC-32, or a custom parameter set.
Why do CRC calculators sometimes return different results?
CRC results depend on more than the polynomial. Width, initial value, input reflection, output reflection, final XOR value, input encoding, and byte order must all match. A difference in any one of these settings can produce a different checksum.
Can I calculate the CRC of a binary file?
Yes. Select the file input option and choose a binary file. The calculator reads the file as bytes and computes the selected CRC directly in your browser.
Are uploaded files sent to a server?
No. CRC calculations and file processing are performed locally in the browser. Your files and input data are not uploaded to the website server.
What is the standard CRC check value for 123456789?
The ASCII string 123456789 is commonly used as a standard CRC test input. The expected result depends on the selected algorithm. For example, CRC-32/ISO-HDLC produces 0xCBF43926, while CRC-16/MODBUS produces 0x4B37.