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any alphabet · custom length · web crypto · local

Generate IDs from a custom alphabet

Define your own charset and length, then mint short IDs with collision-resistance stats. Web Crypto powered, fully offline.

Custom Alphabet ID Generator
Alphabet
36
unique chars
Length
10
per ID
Space
3.66e+15
combinations
Collision
~1.37e-6%
@ 10k samples
LengthCount 10
input · alphabet

Duplicate characters are auto-deduplicated. For URL-safe IDs stick to A–Z, a–z, 0–9, - and _.

Collision math assumes a uniform distribution over the unique-character alphabet.

output · ids (0)

Click Generate to mint IDs

Quick Start

How to design an ID

Two knobs: alphabet size and length. The search space is size^length, and the collision risk for a sample of N is roughly N²/2·space.

  1. 01

    Pick an alphabet

    Start with a charset you can type and share — base32 if you want unambiguous, base62 if URL-safe.

    Bytes flow through TextEncoder/TextDecoder for predictable UTF-8 semantics — emoji, surrogate pairs, and combining marks all encode losslessly.

    alphaUTF-8TextEncoderlosslesslive
    alpha · raw bytesbase32 · UTF-8
    0-9A-Z
    loaded · UTF-8MIME · ready
  2. 02

    Pick a length

    Longer means more space and lower collision risk.

    Hash and signature operations call crypto.subtle from the Web Crypto API, so output matches OpenSSL / Node bit-for-bit.

    lenWeb Cryptosubtledeterministiclive
    len · options10 · live
    AB12CD34EF
    options applied · livelive
  3. 03

    Read the math

    The space and collision stats update live as you tweak inputs.

    Options re-run instantly through useEffect + useMemo — switching URL-safe mode or padding doesn’t re-encode from scratch.

    mathmemoisedoptionsinstantreactive
    space · encoded3.6e15 · ready
    3.6 quadrillion
    encoded · livelossless
  4. 04

    Generate and copy

    Mint as many as you need and copy or download in one click.

    Copy uses the Async Clipboard API; downloads ship via Blob with the appropriate MIME (text/plain, image/png, …) so external tools recognise them.

    exportclipboardblobMIME-correctclient-side
    ok · copiedready · done
    Copied
    shipped · ready to shipsuccess
Pro tips

Encoding without surprises

Always UTF-8 first

Use TextEncoder / TextDecoder for bytes ↔ string conversion. btoa alone breaks on non-ASCII.

URL-safe vs standard Base64

Standard uses +, /, =; URL-safe swaps to -, _, no padding. Don’t mix them.

Hashes aren’t passwords

SHA-256 is fast; that’s good for fingerprints, bad for passwords. Use bcrypt / argon2 for credentials.

Watch padding rules

Some decoders are strict about = padding, others auto-pad. If round-trips fail at exactly 1 or 2 bytes, check padding.

Use Web Crypto for keys

Generate cryptographic keys via crypto.subtle, never Math.random. The latter is predictable.

JWT decode ≠ verify

Decoding a JWT just splits and base64-decodes. Verification needs the issuer’s public key / shared secret.

Related toolsNano IDShort URL KeyUUID v4ULIDCUID2Sequential
Use Cases

When to roll a custom alphabet ID

URL shorteners, coupon codes, license keys.

URL shorteners

Tune length and charset to balance compactness with collision risk. Output round-trips losslessly with the matching decoder — both run client-side, so end-to-end testing happens in a single tab. Encoding flows through TextEncoder for predictable UTF-8 semantics.

RFC-compliant

Coupon codes

Use an unambiguous charset (no 0/O, 1/I/l) for hand-typed codes. Web Crypto's subtle.digest produces output that matches OpenSSL, GPG, and Node's crypto module byte-for-byte. That makes the result trustworthy as a content fingerprint, ETag, or integrity check.

OpenSSL-matched

License keys

5-char groups separated by dashes — set length 25 and split visually. Pairs cleanly with HMAC, JWT, and signed-URL workflows where bit-level correctness matters. The browser's crypto stack is FIPS 140-validated in Chrome and Firefox, so it's production-grade.

lossless

Invite codes

Lowercase+digits for friendly invite codes in beta tools. Output uses canonical RFC 4648 / 7515 alphabets so curl, openssl, and any standards-compliant decoder accept it as input. URL-safe variants drop padding for tokens that travel in query strings.

byte-identical

Test fixtures

Predictable-shape IDs for stable test snapshots. Heavy hashing runs through useMemo so large inputs don't block typing. PBKDF2, bcrypt, and Argon2 expose configurable cost factors — tune for your threat model, not the default.

spec-grade

QR-friendly

Stick to alphanumeric to keep QR codes small. Same input plus same options always yields identical bytes. That's the foundation for content-addressed storage (IPFS, Git, S3 ETags) and means the output is safe to commit to fixtures.

production-ready
FAQ

Frequently asked questions

Duplicates skew the distribution. We collapse to the unique-character set so each character has equal probability.
crypto.getRandomValues fills a Uint8Array, then each byte is mapped to a character via modulo. For uniformity, choose alphabet sizes near 256.
It's a classic birthday-bound approximation for a sample of 10k. Real numbers differ slightly but the order of magnitude is honest.
Theoretically unlimited — practical limits are usability and uniformity of the modulo distribution.
No. ID generation runs locally in your browser via Web Crypto.
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