What is MD5?
MD5 is a hash function that turns any input into a 128-bit (32-character hexadecimal) fingerprint. It was once popular for checksums and password storage, but it is now considered insecure: attackers can create two different inputs with the same MD5 hash (a collision).
Example
The MD5 of hello is 5d41402abc4b2a76b9719d911017c592. The same input always produces the same hash.
When MD5 is still acceptable
- Verifying a non-security file download against a published MD5 checksum.
- Generating cache keys or deduplication fingerprints where collisions are not an attack risk.
- Working with legacy systems that require MD5.
When never to use MD5
- Hashing passwords — use a slow algorithm like Argon2 or bcrypt.
- Digital signatures or integrity where tampering matters — use SHA-256 or stronger.
Privacy: Hashing runs entirely in your browser.