CRC Calculator
Calculate and analyze CRC checksums for data integrity verification.
What Is a CRC?
A Cyclic Redundancy Check (CRC) is a short checksum computed from a block of data, designed to catch accidental corruption — a flipped bit from a bad network link or storage error — not to provide cryptographic security. This tool supports dozens of standard CRC-16 and CRC-32 variants, including CRC-16/MODBUS, CRC-16/CCITT-FALSE, and CRC-32/ISO-HDLC.
How to Use the CRC Calculator
- Enter data as text or hex bytes.
- Choose the CRC variant matching your protocol or file format.
- Read the computed checksum, or use the frame/Modbus tools to build and validate a complete data frame.
Technical Notes
- CRC is for error detection, not tamper resistance — it's easy for someone to intentionally modify data and recompute a matching CRC, which a cryptographic hash or MAC is designed to prevent.
- Different CRC variants use different polynomials, initial values, and bit orderings, so the same data produces a different checksum under each variant — always match the exact variant your protocol or file format specifies.
Frequently Asked Questions
Is a CRC a secure hash?+
No. A CRC only detects accidental changes such as transmission noise or storage errors. It is trivial to alter data and recompute a matching CRC on purpose, so use a cryptographic hash or an HMAC when you need tamper resistance.
Why does the same data give different CRC values in different tools?+
Because "CRC-16" or "CRC-32" alone is not a full specification. The result depends on the polynomial, the initial value, whether input and output bits are reflected (RefIn/RefOut), and the final XOR value. Match the exact named variant your protocol or file format defines.
What do polynomial, init, RefIn/RefOut, and XorOut mean?+
The polynomial is the divisor that defines the CRC. Init is the starting register value. RefIn and RefOut control whether input bytes and the final result are processed least-significant-bit first. XorOut is a constant XORed into the final value. Together these five parameters fully define a CRC variant.