SHA digests computed by your browser's own crypto engine. The text never leaves the page.
Your text is encoded as UTF-8 bytes and passed to crypto.subtle.digest, the hashing function built into the browser itself. The resulting bytes are printed as lowercase hexadecimal, which is the format checksum files and most command-line tools use. Change a single character and the whole digest changes — that is the property that makes hashes useful for verifying that a file or message arrived intact.
The browser's built-in crypto engine does not provide MD5, and adding it would mean loading extra code for an algorithm that has been broken since 2004. If you need MD5 for a legacy checksum, use a command-line tool.
Not directly — hashing is one-way. But short or common inputs can be found by guessing and comparing digests, which is why passwords need salting and a slow algorithm rather than a bare SHA hash.
Not for signatures or security. Practical collisions were demonstrated in 2017. It is included here because plenty of older systems still report SHA-1 checksums that you may need to match.
SHA-256 for almost everything. SHA-384 and SHA-512 give longer digests and are marginally faster on 64-bit hardware, but SHA-256 is the common default.