SHA-256 hash
Compute a SHA-256 digest of any file, on your device.
Runs on your device. The file is never uploaded.
SHA-256 hash reads the bytes of any file and prints a 256 bit digest as 64 lowercase hex characters, under a line naming the algorithm and your file. It exposes no settings, so one file always produces one digest. Hashing tells you whether two files match; it cannot tell you what changed.
Questions
How long is a SHA-256 digest?
256 bits, printed as 64 lowercase hex characters. The output is two lines: the algorithm and your file name, then the digest. There are no options, so the result depends only on the bytes in the file, and changing a single bit anywhere in it changes the whole digest beyond recognition.
Is SHA-256 broken?
No. Unlike MD5 and SHA-1, there is no public collision attack on SHA-256, and it is the ordinary choice for file integrity, code signing and certificates today. If you are picking a hash for something new and have no other constraint, this is the sensible default on this site.
Is this different from the File checksum tool?
Only in the plumbing and the file count. This tool computes SHA-256 with hash-wasm and takes as many files as you drop, one digest each. File checksum uses your browser WebCrypto and takes one file per run, with SHA-1 and SHA-512 as its other choices. The digests are identical either way.
Will this match sha256sum on Linux?
Yes, for the same bytes. Both print the same lowercase hex digest; only the line layout differs, since sha256sum puts the digest first and the file name after it, while this tool puts the name on the first line and the digest on the second. Compare the hex, not the whole line.
Does hashing change or upload my file?
Neither. The file is read to compute the digest and is left exactly as it was, and nothing leaves this tab. A single flipped bit anywhere in the file changes the whole digest, which is the property that makes it useful for spotting a corrupted or altered copy.
How do I check a file against a checksum I was given?
Use Checksum verify rather than reading hex off the screen. You paste the expected value, pick sha256, and it prints MATCH or MISMATCH after trimming whitespace and lowercasing both sides, so a byte identical file cannot fail on formatting alone. The same page also covers md5, sha1, sha384, sha512 and crc32.