What this does
- Shows the SHA-256, SHA-1 and MD5 checksums of a file
- Compares them with a value you paste in, ignoring spaces and capital letters
- Warns when the contents do not match the file’s extension, and loudly when a program is disguised as a document or picture
What it can’t do
Tell you whether a file is safe. A matching checksum proves the file is the one the publisher listed, nothing more.
A worked example
Someone downloads an installer from a mirror site. The project’s own website lists a SHA-256 value. They paste it here; it matches, so the mirror delivered the genuine file.
Questions
- What is a checksum for?
- A checksum, or hash, is a short fingerprint of a file. Software publishers list one beside a download. If the fingerprint of your copy matches, the file arrived complete and unaltered.
- Which one should I compare?
- SHA-256. MD5 and SHA-1 are shown because some sites still publish them, but they only guard against accidental damage, not deliberate tampering.
- What is the type check?
- The tool looks at the first bytes of the file to see what it really is. A file named invoice.pdf that is in fact a Windows program is a common trick in email attachments.
- Can it check a very large file?
- Yes. The file is read in pieces, so its size is limited only by your patience.
Your file stays on this device
The tool above runs in a sealed frame that cannot send your file anywhere. It works with airplane mode on, and the counter above it stays at 0. Here is how you can check that yourself.
Related tools
- Encrypt or decrypt a file Lock any file with a passphrase before you send it, or open one you were sent.
- Check a QR code See where a QR code leads before you open it.
- Remove metadata Strip location, device and hidden previews from photos and documents.
- Redact PDF Black out names, emails and numbers so they are gone for good.
- Redact image Cover parts of a screenshot or photo with solid boxes.
- Find hidden content Check a PDF or Office file for hidden text, sheets, comments and tracked changes.