About Checksum.io

Free, private checksum tools. Built by one developer who got tired of "upload your file to check its hash" sites.

What this site is

A small suite of hashing tools — SHA-256 and friends, a download verifier, a batch SHA256SUMS tool — that run entirely inside your browser. It exists because verifying a download shouldn't require installing anything, reading a man page, or uploading the file to a stranger's server. Everything here is free, with no accounts and no limits.

How it works — and why you can check that claim

The math runs on your machine: your browser's built-in WebCrypto engine handles the SHA family, and the open-source hash-wasm library (MIT licensed, self-hosted here) covers MD5, SHA-3, BLAKE3, CRC-32 and streaming file hashing via WebAssembly. Files are read in 4 MB slices in a background worker, so nothing is ever loaded whole into memory — and nothing is ever transmitted.

Don't take that on faith. Open your browser's developer tools, watch the network tab, and hash something: you'll see the page load its own scripts and then go silent. Load a tool, disconnect from the internet, and it keeps working. The site is plain static files — view-source shows you everything it does.

Privacy

No analytics scripts, no cookies, no fingerprinting, no ads, no accounts. Your files, text, and keys never leave your device — hashing happens locally, full stop. The only thing stored anywhere is your light/dark theme choice, in your own browser's localStorage. The site is served as static files from a CDN; standard delivery logs at the edge see page requests, never your data.

Correctness

A hashing site that's ever wrong is worse than none. Every algorithm here is continuously tested against official test vectors and cross-checked against independent implementations — including streaming multi-gigabyte inputs — before any change ships. If you ever find a value this site disagrees with sha256sum about, that's a serious bug: please report it.

Contact

Questions, corrections, or a tool you wish existed: mail@checksum.io.