File hash checker — verify a download’s checksum

How to verify a download's checksum

1. Drop the downloaded file onto the panel above. Any size and any type. The file is read from your disk in slices, never uploaded.
2. Paste the checksum the publisher gave you. A bare hex string, a whole sha256sum line, a BSD-style SHA256 (file) = … line, or a colon-separated fingerprint all work. The algorithm is detected from the digest length and enabled automatically.
3. Wait for the pass to finish. Throughput and progress are shown as it goes, and you can cancel at any point.
4. Read the verdict. A match means the file on your disk is byte-for-byte the file the publisher hashed. A mismatch means it is not — do not open it.

Why an upload-based checksum tool is the wrong idea

The point of verifying a checksum is to establish that a file you do not fully trust is genuine. Uploading that file to a website inverts the whole exercise: you hand the suspicious bytes to a third party and then trust their word about them. You also pay to upload potentially gigabytes, and you have no way of knowing what happens to the file afterwards.

Verification only means anything where the file already is. This page reads the file directly from your disk with the File API, hashes it locally, and makes no network requests at all after it loads — you can confirm that in your browser's network panel while a 10 GB image is being processed.

Which algorithm should you use?

Algorithm	Digest size	Hex characters	Status
MD5	128 bits	32	Broken for security. Collisions are trivial to construct. Fine for spotting corruption.
SHA-1	160 bits	40	Broken since the 2017 SHAttered collision. Legacy checksums only.
SHA-256	256 bits	64	The current default for release checksums, signatures and integrity checks.
SHA-512	512 bits	128	SHA-2 with 64-bit words. No stronger in practice, often faster on 64-bit CPUs.

The distinction that matters is between accidental and deliberate change. For catching a download that got truncated by a flaky connection, MD5 is perfectly adequate — a corrupted file will not produce a matching digest by chance. For proving that nobody swapped the file for a malicious one, MD5 and SHA-1 are useless: an attacker who controls the file can construct a different file with the same digest. Use SHA-256 whenever the publisher offers it, and treat a project that only publishes MD5 as a mild warning sign.

A checksum does not prove authenticity on its own

If the checksum sits on the same web page as the download link, an attacker who can replace the file can also replace the checksum. Checksums protect against corruption and against a compromised mirror; they only protect against tampering when you get the digest from an independent source — a signed release file, the project's signing key, a different domain, or a copy you saved earlier.

Hashing very large files in a browser

The browser's native crypto.subtle.digest is fast but has no streaming interface: it wants the whole input in memory at once, which rules out anything bigger than a couple of gigabytes. This tool therefore uses native digests for small files and switches to its own incremental implementations of MD5, SHA-1, SHA-256 and SHA-512 for large ones, feeding them 4 MB at a time and yielding to the browser between slices so the page stays responsive.

Peak memory stays in the low megabytes regardless of file size, so the practical limit is how fast your disk can be read rather than how much RAM you have. The implementations are checked against the standard FIPS 180-4 and RFC 1321 test vectors, including the awkward cases around block and padding boundaries.

The checksums do not match — now what?

1. Check you are comparing the right algorithm. A SHA-256 digest will never match an MD5 one. The tool detects this from the length, but a publisher listing several files can make it easy to grab the wrong line.
2. Check you have the right file. Different architectures, editions and point releases have different checksums, and browsers sometimes append (1) to a re-downloaded file rather than replacing it.
3. Download it again, ideally from a different mirror. Most mismatches are interrupted or truncated downloads, and a second attempt fixes them.
4. If it still does not match, stop. Do not run the installer to "see what happens". Report it to the project, and get the file from the canonical source.

Command-line equivalents

Everything here matches what your operating system's own tools produce, so you can cross-check:

sha256sum ubuntu-24.04.iso            # Linux
shasum -a 256 ubuntu-24.04.iso        # macOS
certutil -hashfile ubuntu.iso SHA256  # Windows
Get-FileHash ubuntu.iso -Algorithm SHA256  # PowerShell

The digests are identical — a hash function has exactly one correct answer for a given set of bytes. This page simply saves you from remembering which of those four commands your current machine wants.