What's the difference between $2a$, $2b$, and $2y$?

Versioned variants of bcrypt. $2a$ was the original (had a sign-extension bug). $2b$ is the corrected version. $2y$ is a PHP-specific variant equivalent to $2b$. All three are accepted; modern libraries emit $2b$.

Why doesn't my password match the hash?

Most common causes: copy-paste added a trailing newline or space; the hash was for a different password; or the hash was generated by a non-bcrypt algorithm (scrypt, Argon2) and just looks similar. Check the hash starts with $2[a|b|y]$.

Can I get the password from the hash?

No — bcrypt is one-way. You can only verify (does plain text match hash?). To 'recover' a forgotten password you'd have to brute-force every possible candidate, which is what bcrypt is specifically designed to make infeasible.

Is my password sent anywhere?

No — verification runs entirely in your browser. Even the network tab shows zero outbound requests.

bcrypt · compareSync · local · no upload

Verify a bcrypt hash against a password

Paste a plain text password and its bcrypt hash to confirm whether they match. Uses bcryptjs.compareSync entirely in your browser — nothing leaves the page.

bcrypt Hash Verifier

Status

idle

live

Cost

—

rounds

Hash len

—

0 B

Algo

bcrypt

$2a/$2b/$2y

input · password + hash

Plain text passwordbcrypt hash

Supports $2a$, $2b$, $2x$, and $2y$ hashes. The hash carries its own salt and cost factor — no extra config needed.

output · verification

Press Verify to compare

Quick Start

How to verify a bcrypt hash

bcrypt stores a salt and a cost factor inside the hash, so you only need the plain password and the hash to verify. compareSync handles timing-safe comparison automatically.

01
Paste plain password
The string you think should hash to the value below.
Inputs are treated as UTF-8 throughout the pipeline and validated client-side as you type — nothing dispatches until the value is well-formed.
passwordinpututf-8client-sidevalidated
in · textsecret · set
```
••••••••
```
loaded · parsedclient-side
02
Paste bcrypt hash
A $2a$/$2b$/$2y$ hash from your database or seed file.
Each toggle re-computes through a memoised hook, so flipping options never resets your input and the UI stays snappy on large inputs.
hashoptionslivememoisedtoggles
hash · memoised$2b$12 · live
```
$2b$12$....60chars
```
options set · memoisedlive
03
Click Verify
bcryptjs derives a candidate hash with the same salt + cost and compares.
Randomness — where used — comes from crypto.getRandomValues, never Math.random. Heavy work sits in useMemo.
comparecomputeinstantlocaldeterministic
compare · instantlive · computed
```
compareSync(plain, hash)
```
computed · instantinstant
04
Read the verdict
OK means the password is correct. X means it does not match.
Copy writes through navigator.clipboard and downloads use a Blob — zero network traffic. Same input plus same options always yield the same bytes.
verdictcopydownloadzero-networkreproducible
ok · copiedmatch · copied
```
Password matches hash
```
shipped · ready to shipsuccess

Pro tips

Pro tips for everyday utilities

Reach for crypto.getRandomValues

Cryptographically random for IDs, tokens, salts. Math.random is for animation and games, not security.

Sort IDs lexicographically

UUID v4 has no time ordering. Use ULID or UUID v7 if you need sorted IDs.

Mock data with seeds

Faker-style libraries can be seeded so tests are reproducible. Embed the seed in the fixture file.

Reference cards beat memory

Cheatsheets for Vim, Git, Docker, Linux signals are faster than man pages when you’re mid-flow.

Browser APIs vary

Touch events, gamepads, and clipboard differ across vendors. Feature-detect before use.

Persist in the right place

localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data.

Use Cases

When to verify a bcrypt hash

Debug failing logins

Confirm the stored hash actually matches the password your user thinks they have. Random values come from crypto.getRandomValues — cryptographically secure for tokens, salts, and session IDs. Math.random is deterministic enough for animations but predictable enough to be a security bug.

CSPRNG-backed

Audit seed data

Check test-account passwords in seed files before pushing. Pair with hashids, ULID, or UUID v7 when you need both random and sortable — useful for primary keys, public-facing IDs, and event log ordering without a sequence column.

reproducible

Migrations

Verify hashes after copying between databases or formats. Output is deterministic given the same seed, so fixtures and tests stay reproducible across CI runs and contributor machines. Embed the seed in the fixture file for full replay.

snappy

Recover legacy

Spot-check users whose old bcrypt hashes still work. Heavy work runs through useMemo so the UI stays snappy on large inputs. Same input + same options yields identical bytes — the kind of stability snapshot tests rely on.

feature-detected

Cost tuning

Compare verify time for different cost factors locally. Storage tools persist to the right backend: localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data. Pick the right shelf and quota worries disappear.

deterministic

Education

Show how bcrypt salts and cost factors live inside the hash. Browser feature detection: clipboard, fullscreen, gamepad, and Web Bluetooth APIs gracefully fall back when unavailable. No surprise white screens on Safari or older Firefox.

production-ready

FAQ

Frequently asked questions

Why bcrypt and not SHA-256?

bcrypt is purpose-built for passwords. Plain SHA-256 is fast — attackers can brute-force billions per second. bcrypt's tunable cost factor slows that down by design.

What is the cost factor?

The number after $2b$ is the log2 of the rounds. 12 means 2^12 = 4096 iterations. Each step doubles the time to verify.

Is $2a$ different from $2b$?

$2b$ is the current canonical prefix; $2a$ and $2y$ are older but supported. bcryptjs accepts all three.

Does it support Argon2?

No — only bcrypt. Use a dedicated Argon2 verifier for $argon2id$ hashes.

Is the password sent to a server?

No. Verification runs locally in your browser via bcryptjs — nothing leaves the page.

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