File Hash

📖 Tool Introduction

File Hash is a fully offline digest tool that implements the SHA-256 and SHA-1 standards in pure JavaScript inside your browser. It can fingerprint any file byte by byte, or hash the text you paste directly. On startup it runs a built-in known-answer self-test against the official vectors: SHA-256("abc") must equal ba7816bf…0015ad, SHA-256("") must equal e3b0c442…b855, and SHA-1("abc") must equal a9993e36…d89d. If the self-test fails, the tool refuses to run, so a wrong digest can never come out of it. Large files are streamed into the hash core in four-megabyte chunks while a progress bar moves in real time, which keeps memory usage flat and avoids freezing the tab. Digests are the standard way to verify that a downloaded file arrived intact, to confirm that two copies of something are byte-for-byte identical, or to build a fingerprint archive of sensitive documents. Because the whole computation never leaves your browser, you can hash confidential files without any worry about leakage. The interface offers a one-click switch between file mode and text mode, lets you tick either or both algorithms independently, and provides a dedicated copy button beside every digest row. Press Ctrl+Enter in text mode to fire a computation without touching the mouse, and the example button loads the classic test string "abc" so you can watch both digests appear in one click.

✨ Key Features

• Dual algorithms: SHA-256 (64 hex chars) and SHA-1 (40), freely combined
• Dual modes: file mode hashes bytes, text mode hashes what you type
• Streaming chunks: large files feed the core in 4 MB slices with constant memory
• Known-answer self-test: official test vectors guard algorithm correctness
• Live progress: the bar advances while hashing, no black screen on long jobs
• Zero uploads: pure frontend, safe even for classified files

📝 How to Use

1. Tick SHA-256 and/or SHA-1 in the algorithm area
2. In file mode, drop or pick the file you want to verify
3. In text mode, paste the string you want to digest
4. Click Compute hash and wait for the progress bar to finish
5. Use the copy button beside each digest to paste the fingerprint into a checklist

⚠️ Notes

• Pick at least one: with no algorithm ticked the tool shows a friendly hint
• SHA-1 weakness: keep SHA-1 for legacy compatibility and prefer SHA-256 for new work
• UTF-8 text: text mode hashes the UTF-8 bytes, matching the file mode convention
• Hex case: output is lowercase hex, so mind the case when comparing to official values
• Huge files: hundreds of megabytes take seconds to tens of seconds, which is normal

🧰 Common use cases

Cryptographic hashes answer two everyday questions: is this file exactly the same as the copy I already have, and did this download finish intact without corruption. Software mirrors publish SHA-256 sums so you can verify an installer before running it; archivists compare a restored backup against the original to prove bit-for-bit equality; programmers checking whether two exports are duplicates can hash both and compare the short fingerprints rather than opening whole folders. The implementation here runs entirely in JavaScript and streams the file in chunks, so multi-gigabyte videos never load all at once into memory; a tiny built-in selftest at startup reproduces the published test vectors to prove the algorithm is wired correctly. The text mode is handy for small strings, license keys and notes where you want a digest without creating a file. Remember that a hash proves identity and integrity, not origin or trust: anyone can recompute the same digest, so a published checksum should be fetched from the same source as the file whenever possible.