Hash and UUID generator that works on your device

No. The SHA digests come from your browser's own Web Crypto API and MD5 is computed by plain JavaScript on this page, so the page makes no network request with your data. A file is read into memory on your device and hashed there. You can load the page, go offline, and it still works.

Almost always a newline or an encoding. This tool hashes exactly the bytes you typed, as UTF-8, with nothing added: the MD5 of hello is 5d41402abc4b2a76b9719d911017c592. But echo hello | md5sum hashes hello plus a newline and gives b1946ac92492d2347c6235b4d2611184. Use printf '%s' hello | md5sum or echo -n to match. Windows line endings, a trailing space, a byte-order mark or a different encoding such as UTF-16 change the digest in the same way.

It depends on the job. As a checksum, to spot a corrupted download, a failed copy or a duplicate file, MD5 is fine: an accidental change will not produce the same 128-bit digest. It is not safe where someone could choose the input, because collisions (two different files with one MD5) can be made to order, so it should not stand behind signatures, certificates or software updates; use SHA-256 there. And no fast hash, MD5 or SHA-256, should ever store a password: a graphics card tries billions of guesses a second, so a leaked table of MD5 passwords is cracked in hours. Passwords belong in a slow, salted algorithm built for them, such as bcrypt, scrypt or Argon2.

Drop the file into the tool, then paste the checksum from the download page into Compare with a known hash. The tool says which algorithm it matches, whatever its case, and it understands whole lines copied from sha256sum or shasum output, such as d7a8fb... installer.iso. A match means the file arrived byte for byte as published. No match means the file is damaged, altered or a different version, so do not run it until you know why.

A UUID is a 128-bit identifier written as 32 hex digits in five groups, such as 3f2504e0-4f89-41d3-9a0c-0305e82c3301. Version 4 means the value is random: six bits are fixed to mark the version (the 4 at the start of the third group) and the variant (8, 9, a or b at the start of the fourth), and the other 122 come from your browser's cryptographically secure random number generator. A repeat is possible in theory but not in practice: you would have to generate about 2.7 quintillion UUIDs before the odds of a single duplicate reached 50%, so they are safe to use as database keys and file names without checking.