Double SHA-256 hash generator.

Double SHA-256, often written SHA-256d or Hash256, is SHA-256 applied to the 32-byte digest of SHA-256. Bitcoin uses it for every block hash, every transaction id, the Merkle tree and the four-byte checksum at the end of a Base58Check address.

Mostly to close the length-extension hole. A single SHA-256 digest lets anyone who knows it continue hashing as if more data followed; hashing the digest again hides the internal state, so the output cannot be extended. Satoshi's design also followed Ferguson and Schneier's advice to double-hash as a conservative margin.

Bitcoin's internal byte order. Block hashes and txids are computed as double SHA-256 and then shown with the bytes reversed, so take the digest from this tool and reverse it two characters at a time to match what an explorer prints.

Not meaningfully. It costs twice the work on a short input and the output is as secure as SHA-256's 128-bit collision resistance. Nobody has found a reason to prefer it outside Bitcoin-derived protocols; for a new system, SHA-256 or SHA3-256 is the plain choice.

Nothing leaves your browser. The hash is computed on your machine, by the browser's Web Crypto API or a WebAssembly build of the algorithm loaded on first use, and the page makes no request with your input. You can load the page, go offline and keep hashing.

Drop the file onto the input or choose it with the button, and the tool reads it in your browser and hashes the bytes. Files up to 1 GB work; past that the browser would need the whole file in memory, so the tool declines. Paste the published digest into the Verify field to compare.

Hex is the common form: 64 characters from 0 to 9 and a to f, the same value in upper or lower case. Base64 writes the same 32 bytes in fewer characters, and Base64url swaps + and / for - and _ with no padding. Switch the output and the digest is re-encoded, not recomputed.

Text is hashed as UTF-8 bytes, which is what every language and command line does by default. A trailing newline changes the digest, so `echo -n` or this tool's input, with no newline added, matches a command-line tool run on a file without one.

No. The Double SHA-256 hash generator is free and opens without a sign-in, an account or an install.

Nothing. The Double SHA-256 hash generator holds your input in the page's memory, so closing or reloading the tab clears it, and it saves nothing in this browser.

The toolbar switches to SHA-256 without leaving the page. Each one reads the same input, so you can compare digests side by side.

Double SHA-256 runs on the browser's own Web Crypto API, so there is nothing to download and it is the fastest path.

No: Double SHA-256 has no keyed form here. Switch to SHA-256 in the toolbar to sign with a key.

Yes: the File to Double SHA-256 page has the same algorithms and options and opens on the file pane. Files are read in your browser and never uploaded.

Not on its own. Double SHA-256 is built to be fast, and fast hashes are cheap for an attacker to guess against. Passwords need a salted, deliberately slow hash: use Argon2id, Argon2d, and bcrypt from the hash generators, which draw a fresh random salt each time.

Closest to the Double SHA-256 hash generator: File to Double SHA-256, SHA-256 hash generator, RIPEMD-160 hash generator, Keccak-256 hash generator. Each opens on its own page, free and in the browser.

The Double SHA-256 hash generator is one of 64 in its group. The group's page, /tools/hash, lists them all.

The tool is free. Its interface is built from shadcn.io's own components (Button, Input, Slider and the rest of the registry under /ui), which come in React, Vue, Svelte and Solid. Pro adds the blocks and templates for the product around it.