CRC32 checksum
Compute a CRC32 digest of any file, on your device.
Runs on your device. The file is never uploaded.
CRC32 checksum prints a 32 bit polynomial remainder as 8 lowercase hex characters, the value zip entries and PNG chunks carry over their own contents. hash-wasm computes it and there is nothing to configure. It detects accidental damage and no more: a match can be arranged deliberately, and 8 characters collide by chance too.
Questions
Is CRC32 secure?
No. CRC32 is an error detection checksum, not a security hash. It is designed to catch accidental corruption from a bad disk, a truncated copy or a noisy link, and it is easy to construct a different file with the same value on purpose. Never use it to decide that a download was not tampered with. Use SHA-256 hash for that.
How long is the output?
32 bits, printed as 8 lowercase hex characters. That is short enough that accidental collisions between unrelated files are entirely possible, which is another reason it is a corruption check rather than an identity. The value appears under a line giving the title and your file name.
Which CRC32 variant is this?
The crc32 function from hash-wasm, the same family of value that zip and PNG use. CRC32C, the Castagnoli polynomial used by iSCSI and some filesystems, is a different variant and is not available on this site, so a value from a CRC32C tool will not match this one.
Why does this not match the CRC in my zip file?
Because a zip stores a CRC-32 of each entry uncompressed contents, not of the archive file itself. Hashing the .zip with this tool checksums the container. To compare, extract the entry first and run the checksum over the extracted file.
Can I checksum several files at once?
Yes. Each file gets its own result: the title, your file name, and the 8 character value underneath. There are no options to set, nothing leaves your device, and the WebAssembly implementation runs in a Web Worker so a large file does not block the page while it reads.