Generate a SHA-256 hash

A hash is a short fingerprint of some input. The same input always produces the same digest, and changing a single byte produces a completely different one. That property is what makes hashes useful for checking that a file arrived intact and unmodified.

The usual reason to want one is verification. A project publishes the SHA-256 of its installer, you compute the hash of the copy you downloaded, and the two strings either match or they do not. If they differ, the download is corrupt or it is not the file the publisher released. Doing that check on a website that asks you to upload the file first is self defeating, because the upload is the part you were trying to avoid. Here the file is read by the browser and hashed in the page.

Text hashing works the same way. Text input accepts up to 2 MB, and files are read in one pass without being copied to a server.

Two limits are worth stating plainly. A hash proves a file matches a checksum, but only if the checksum itself came from a trustworthy place, so read it from the publisher’s own site rather than from the same page that hosted the download. And hashing is not encryption: it cannot be undone, but a short or common input can be found by guessing, which is why passwords need a purpose-built algorithm with a salt rather than a bare SHA-256.