How I Built a Free Hash Generator That Runs 100% in Your Browser

Description and use

Built a client‑side hash generator that runs entirely in the browser, supporting MD5, SHA‑1/256/384/512 and HMAC, using WebCrypto and a hand‑rolled MD5 implementation, with streaming for large files and instant UI updates.

Problem

Users need a client‑side hash generator that supports MD5, SHA‑1/256/384/512 and HMAC without sending data to a server.

Outcome

The hash generator runs entirely client‑side, supports all common hash algorithms, handles large files via streaming, and provides instant feedback for text input.

Workflow

• 1. User types or pastes text into the Text tab; the component calls crypto.subtle.digest() for SHA algorithms and the custom Md5.update() for MD5, running all five digests in parallel via Promise.all.
• 2. User drops a file in the File checksum tab; FileReader streams the file in 64‑byte chunks, feeding each chunk to the incremental Md5 class or crypto.subtle.digest() for SHA, keeping memory usage low.
• 3. User pastes an expected hash in the Compare tab; the tool auto‑detects the algorithm from the hex length and compares the computed hash to the expected value.
• 4. User enters key and message in the HMAC tab; for SHA algorithms WebCrypto imports the key and signs, while for HMAC‑MD5 the custom MD5 implementation is used per RFC 2104.
• 5. Results are displayed instantly for text input and as soon as the file stream completes for file input.

Evidence

Most free hash tools online paste your input into a form, POST it to a server, and return the digest.

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Browsers no longer ship MD5 in WebCrypto. crypto.subtle.digest() supports SHA-1, SHA-256, SHA-384 and SHA-512, but MD5 was left behind because it's not collision-resistant anymore.

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I wrote an incremental MD5 implementation straight from RFC 1321… I can hash a 100 MB file in chunks without loading it all into memory.

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One gotcha worth knowing: crypto.subtle.digest() is async and takes an ArrayBuffer… The tool computes all five digests in parallel with Promise.all for text input, so the UI updates essentially instantly.

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The UI is four tabs, one per question people actually ask… Real example: after downloading a Linux ISO, the mirror usually publishes a SHA-256 checksum… Doing this without uploading a 3 GB file to someone's server is the entire point of building it client-side.

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