You just downloaded an installer, a firmware update, or a dataset. The page listed a "SHA-256" string next to the link, but the download went straight to your machine and you moved on. That hash exists for one reason: so you can confirm the file you got is the file they published — not a corrupted copy, and not something swapped in along the way.
Doing the check locally is the honest way to do it. The File Checksum tool reads the file on your device and computes SHA-1, SHA-256, and SHA-512 in the browser. Paste the published hash into the "Expected hash" box and it tells you whether they match. The file never leaves your tab — you're not handing a stranger's server the very binary you're trying to vet.
Why it matters: a mismatched hash means the download was altered or truncated. Some mirrors serve stale or incomplete files, and a flipped bit in firmware can brick a device. A ten-second check turns "I hope this is right" into "I know this is right."
Before you check, it helps to know what you're holding. The File Info tool shows the file's size and MIME type so you can sanity-check it against what the publisher described.
Quick path: download the file, open File Checksum, point it at the file, paste the published hash, and read the match result. If it matches, install or open with confidence; if not, re-download from the source.