Introduction
Looking for a collision-resistant ID that is safer than UUID for DOM elements and distributed systems? CUID (Collision-resistant Unique Identifier) generates sequential, URL-safe identifiers that are designed to avoid collisions across distributed systems while remaining sortable by creation time. This tool generates CUIDs in your browser using the cuid library. Enter a count and click Generate to produce up to 1000 identifiers at once.
What this tool does
- Generates CUID (Collision-resistant Unique Identifier) strings using the cuid npm package.
- Supports generating 1 to 1000 CUIDs in a single batch.
- CUIDs are sequential and roughly sortable by creation time, unlike UUID v4 which is random.
- CUIDs start with 'c' and use only lowercase letters and numbers, making them URL-safe and valid as HTML ID attributes (unlike UUIDs which start with a number).
- All generation happens client-side. No identifiers are transmitted to any server.
How this tool works
Enter the number of CUIDs you want to generate (1 to 1000) in the count field. Click the Generate button and the tool creates that many CUIDs, one per line, in the input field. The output field shows a preview of the first generated CUID. You can also type a number directly into the input field to generate that many CUIDs. Each CUID is unique within the session and across sessions due to the algorithm's use of timestamp, machine fingerprint, and a counter.
How CUID generation works
CUID was created by Eric Elliott to address shortcomings of UUID in distributed systems. A CUID is composed of several parts: a 'c' prefix (ensuring it starts with a letter, making it valid as an HTML ID), a timestamp encoded in base 36, a counter to prevent collisions within the same millisecond, a random fingerprint based on the machine and process, and a random component. The format is: `c + timestamp + counter + fingerprint + random`. The timestamp provides rough sortability. The counter ensures uniqueness within the same millisecond on the same machine. The fingerprint helps distinguish between different machines or processes. The random component adds entropy. CUIDs are 24+ characters long and use only lowercase letters and numbers (base 36), making them URL-safe and safe to use as DOM element IDs. Unlike UUID v4, which is purely random and has no sort order, CUIDs can be roughly sorted by creation time. This is useful for database indexes and log entries. CUID2 is the successor to CUID, offering improved security and collision resistance. The original CUID library (cuid on npm) is used by this tool. Note that CUID is not cryptographically secure. For security-sensitive identifiers, use UUID v4 with crypto.getRandomValues, or NanoID with a cryptographically secure random number generator.
How to use this tool
- Enter the number of CUIDs you want to generate (between 1 and 1000) in the count field.
- Click the Generate button. The tool creates the specified number of CUIDs, one per line.
- Review the generated CUIDs in the input field. Each line is a unique identifier.
- Use the Copy result button to copy the output to your clipboard.
- Click Generate again to create a new batch of CUIDs if needed.
Real-world examples
Generating IDs for a batch of database records
Set count to 100 and click Generate. The tool produces 100 unique CUIDs like `clh3a4p5e0000l3w8d1f2g3h`, `clh3a4p5e0001l3w8d1f2g3i`, etc. Use these as primary keys for database inserts where you need pre-generated IDs.
Creating unique DOM element IDs
Generate a single CUID and use it as the id attribute for a dynamically created DOM element. CUIDs always start with 'c', making them valid HTML IDs (which cannot start with a number). UUIDs starting with a number would require a prefix.
Generating test fixtures
Set count to 50 and click Generate. Copy the 50 CUIDs into your test fixture file. Each test run uses the same set of unique, non-colliding identifiers without needing a database sequence.
Comparison with similar methods
| Method | Complexity | Typical use |
|---|---|---|
| CUID | Timestamp + counter + fingerprint + random | Distributed systems, DOM IDs, sortable IDs |
| UUID v4 | 122-bit random | Globally unique IDs, standard format |
| ULID | 48-bit timestamp + 80-bit random | Lexicographically sortable unique IDs |
| NanoID | Random base64url, configurable length | Short URL-safe IDs |
Limitations or considerations
CUID is not cryptographically secure. The random component uses Math.random, not crypto.getRandomValues. Do not use CUIDs for security-sensitive purposes like session tokens or API keys. The cuid package is deprecated in favor of @paralleldrive/cuid2, which offers improved security and collision resistance. CUIDs are longer than UUIDs (24+ characters vs 36 characters with hyphens, but UUIDs are 32 hex characters without hyphens). The timestamp component means CUIDs generated in rapid succession on the same machine are sequential, which could leak information about creation order if that is sensitive.
Frequently asked questions
What is the difference between CUID and UUID?
CUID starts with a letter (making it valid as an HTML ID), is roughly sortable by creation time, and uses base 36 (lowercase letters and numbers). UUID v4 is purely random, uses hexadecimal (0-9 and a-f), and includes hyphens. CUID is designed for distributed systems; UUID is a widely supported standard.
Is CUID deprecated?
The original cuid package is deprecated in favor of @paralleldrive/cuid2, which uses cryptographically secure random number generation and has improved collision resistance. However, the original CUID format is still widely used and this tool uses the cuid package.
Can CUIDs collide?
The probability is extremely low. CUID uses a combination of timestamp, counter, machine fingerprint, and random components. The counter prevents collisions within the same millisecond on the same machine. The fingerprint distinguishes between machines. In practice, collisions are not observed.
Are CUIDs sortable?
Roughly, yes. Because CUIDs encode a timestamp at the beginning, they can be lexicographically sorted to approximate creation order. However, this is not guaranteed to be exact across different machines with different clocks.
Conclusion
This CUID generator provides a fast way to create collision-resistant unique identifiers in your browser. CUIDs are useful for distributed systems, DOM element IDs, and any scenario where you need unique, roughly sortable identifiers. For cryptographically secure IDs, consider CUID2 or NanoID with secure random generation. Check out the related UUID generator and ULID generator tools on this site.