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How to verify a file’s SHA-256 checksum in your browser
Compare a downloaded file with a trusted checksum, troubleshoot mismatches and understand why a matching hash is not a malware scan.
By ToolGrid AI Editorial Team · Published
What a checksum tells you
SHA-256 produces a 256-bit digest, commonly shown as 64 hexadecimal characters. Hashing the same bytes with the same algorithm produces the same digest. A changed file will ordinarily have a different digest, making checksums useful for detecting differences between a download and a trusted reference.
A hash is not a virus scan, and it does not identify a trustworthy author by itself. A malicious file can have a perfectly valid hash. The check is meaningful only if the expected checksum comes from a source you have reason to trust.
Find the reference first
Look for a SHA-256 checksum published by the software vendor or document provider for the exact file version and platform. Do not compare a Windows download with the checksum for a macOS package, or SHA-256 output with a SHA-1 value.
If you received both a file and its checksum from the same untrusted message, an attacker could have changed both. A reference from the publisher’s authenticated site or a signed release provides a stronger basis for comparison, depending on the publisher’s distribution process.
Run the local comparison
Open File SHA-256 Checksum, choose the downloaded file and paste the expected 64-character value. Click Calculate SHA-256. The result shows the computed digest and either MATCH or NO MATCH. Uppercase and lowercase hexadecimal are accepted for the reference.
This implementation reads the file into memory, so it limits selections to 200 MiB. That is a practical browser memory limit, not a cryptographic limitation. For larger downloads, use a trusted operating-system checksum utility and the same reference algorithm.
Troubleshoot a mismatch carefully
Check the version, filename and algorithm first. A ZIP archive and the extracted program inside it have different bytes and therefore different hashes. A text file saved with different line endings or encoding can also produce a different result.
If the exact download still fails to match, do not run it just because the filename looks right. Obtain a fresh copy from the official source or ask the publisher to confirm the reference. Keep the failed copy separate while investigating.
What happens to your file
Hashing uses your browser’s Web Crypto digest operation on the user-selected file. The tool does not need to upload the file to compute the checksum. The displayed digest is much smaller than the file, but can still identify a known file when compared with other hashes.
For important software, combine checksum verification with other appropriate checks, such as a publisher signature and your organization’s security process. A matching reference is useful evidence about the bytes; it is not a guarantee of safety.
Sources
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