CRC32 & Checksum Calculator

How it is calculated

A checksum condenses text into a short fixed-size value so that accidental changes can be spotted. The tool hashes the exact bytes you type and prints three values in hexadecimal. crc32 is PHP's crc32 algorithm, which is the bzip2 variant of the 32-bit cyclic redundancy check; crc32b is the standard CRC-32 used by ZIP, PNG and Ethernet; adler32 is the Adler-32 sum used by zlib. All are 32 bits (8 hex digits). They detect errors but are not cryptographic: anyone can build different input with the same value. Empty text gives no result, and the checksum covers every character, including spaces and line breaks.

Common mistakes

• Comparing the crc32 line with a ZIP or PNG checksum; those use crc32b, so the values differ.
• Treating a checksum as a secure hash; it is trivial to craft a collision, so use SHA-256 for integrity against tampering.
• Adding a trailing space or newline when pasting, which changes every value.
• Expecting the checksum of a file from its name; the tool hashes the typed text only.
• Mixing text encodings; the same visible text in UTF-8 and another encoding has different bytes and a different checksum.