Hash Lookup Developer Tool
Paste a hash to see if it's in our database, and which algorithm produced it.
If you've got a hash from somewhere else — a file checksum, a leaked credential dump, a log entry — and want to know what algorithm produced it or whether it's already known, this free hash lookup developer tool checks it against MD5, SHA-1, SHA-256, SHA-384, and SHA-512 automatically, based on the hash's length.
Start typing or pasting a hash above to look it up.
How it works
- The hash length tells us which algorithm to check — no need to select one.
- We search every previously saved hash for an exact match.
- A match reports the algorithm and what kind of content it was — a string, JSON object, or file.
Privacy
Only the hash itself is sent for lookup — nothing is saved from this page. Want to generate and save a hash instead? Use the Hash Generator.
How hash identification works
A hash digest carries no metadata about which algorithm produced it — there's no header or tag saying "this is SHA-256." What it does carry is a fixed, algorithm-specific length: MD5 always produces 128 bits (32 hex characters), SHA-1 always produces 160 bits (40 hex characters), SHA-256 produces 256 bits (64 hex characters), and so on through SHA-384 (96 hex characters) and SHA-512 (128 hex characters). Because these lengths rarely collide with each other, checking the length of a hex string is a reliable heuristic for narrowing down which algorithm (or occasionally, a small number of candidate algorithms) could have produced it. This tool applies exactly that heuristic client-side as you type, highlighting the matching badge, before it ever queries the server.
Rainbow tables and why lookup services exist
Because a hash function always produces the same output for the same input, a large enough precomputed table mapping common inputs to their digests — a rainbow table, or more simply a database of known hash-to-value pairs — can turn "what does this hash mean?" into a simple lookup rather than a brute-force search. Security researchers, breach-monitoring services, and this tool's own database work the same basic way: every hash generated through the companion Hash Generator on this site is recorded, so a later lookup of that same digest can report what produced it. This is fundamentally a matching exercise against previously seen values, not a mathematical inversion of the hash function.
Why this doesn't "reverse" a hash
It's worth being precise about what a successful lookup means, because it's a common source of confusion. A well-designed cryptographic hash function is a one-way function: there is no computation that takes a digest and derives the original input from first principles. What a lookup service actually does is check whether that exact digest happens to already exist in a table of known input/output pairs, built either by hashing lists of common values in advance or by recording digests as they're generated (as this site does). If the original input was never hashed and recorded anywhere the service checked, the digest will never resolve, no matter how much computing power is thrown at it — the hash function itself remains intact. A "not found" result here means only that this database hasn't seen that value, not that it's unhashable.
Salting, and why salted hashes won't match a lookup
Password storage systems that follow current best practice (bcrypt, Argon2, or even a salted general-purpose hash) prepend or mix in a random, per-record salt before hashing, specifically so the same password produces a different digest every time it's stored. This defeats rainbow-table and lookup-style attacks outright: even if password123 appears in every precomputed table on earth, a salted hash of it is unique to that one record and won't appear in any lookup database, because nobody else's copy of the same password produced the same digest. If you paste a hash here and get no match, that's not a limitation of this tool — it's the salt (or simply an input nobody has hashed and recorded before) doing exactly what it's supposed to do. Unsalted hashes of common values, by contrast, are exactly what rainbow tables and services like this one are built to catch, which is one more reason unsalted general-purpose hashes are unsuitable for storing anything sensitive.