CUID2 is a collision-resistant unique identifier format built for systems where many machines generate IDs independently, without checking a central database first. It is designed to be hard to guess and safe to use as a primary key.

How is this different from UUID?

A UUID v4 is purely random. CUID2 mixes a timestamp, a counter, and random entropy through a hash, which spreads IDs evenly across sort order and reduces the chance of index hot-spotting in databases compared to some UUID variants.

Are the IDs generated on a server?

No. Everything happens in your browser using the WebCrypto API for random bytes and hashing. No ID, and no data used to build it, is ever sent to a server.

Can two generated IDs collide?

Collisions are astronomically unlikely. Each ID combines a random starting letter, millisecond timestamp, an incrementing counter, and 128 bits of cryptographic randomness before hashing, giving a large effective ID space.

Are these IDs safe to expose in a URL?

Yes. CUID2 output uses only lowercase letters and digits, so it is URL-safe without any encoding.

CUID Generator

Generate collision-resistant CUID2 identifiers instantly in your browser, with a count selector and one-click copy.

Generate CUID2s

How many?

Click Generate to create CUID2 identifiers

Copied!

Summary

CUID2 is a collision-resistant identifier designed for horizontally scaled systems, where multiple servers or clients generate IDs without a central coordinator. This generator builds each ID from a random starting letter, a timestamp, a session counter, and cryptographically random bytes, hashed together with WebCrypto so the output cannot be predicted or reverse-engineered. Everything runs locally in your browser; no ID is sent anywhere.

How it works

Choose how many IDs to generate from the count selector.
Click Generate to create that many CUID2 strings.
Each ID mixes a random letter, timestamp, counter, and WebCrypto random bytes hashed together.
Click any single ID to copy it, or use Copy All to copy the full list.

Use cases

Primary keys for database records in distributed systems.
Unique identifiers for client-generated records before they sync to a server.
Test fixtures that need realistic, non-sequential IDs.
Session or request IDs for logging and tracing.
Short, URL-safe IDs for public-facing resources.
Seeding sample data for demos and local development.

Frequently Asked Questions

Last updated: 2026-09-09 · Reviewed by Nham Vu