Adler32 Checksum Calculator

Adler-32 is a checksum used to quickly detect accidental data corruption, most notably inside the zlib compression library (which underlies PNG, gzip, and ZIP), and in some network protocols. It's designed to be fast to compute, not to resist deliberate tampering.

No, Adler-32 is a checksum, not a cryptographic hash. It's much faster to compute and produces a smaller 32-bit value, but it isn't designed to resist someone deliberately crafting different input with the same checksum, the way MD5 or SHA-256 are (at least in principle). Use a cryptographic hash if you need tamper resistance, not just accidental-error detection.

The algorithm starts with two running sums initialized to 1 and 0, and combines them into the final checksum even if no bytes are processed, so an empty input always produces the same fixed value: 1 (0x00000001) rather than 0.

Text is encoded as UTF-8 before the checksum is calculated, the same encoding used by most modern text files and web pages. This matters because the same text can produce a different checksum under a different encoding.

Yes, switch to "File" mode and choose a file, its checksum is calculated directly from its raw bytes, useful for verifying that a downloaded or transferred file matches an expected checksum.