UUID and NanoID are two of the most common ways to generate unique identifiers without a central authority. Both produce collision-resistant values suitable for primary keys, tokens and resource IDs, but they differ in format, length, ecosystem support and practical trade-offs.
This article compares UUID v4 and the default NanoID configuration so you can decide which fits a given project.
Quick comparison
| Feature | UUID v4 | NanoID (default) |
|---|---|---|
| Length | 36 characters (with hyphens) | 21 characters |
| Alphabet | Hex (0-9, a-f) | URL-safe (A-Za-z0-9_-) |
| Random bits | 122 | ~126 |
| Collision resistance | Extremely low | Comparable to UUID v4 |
| URL-safe | No (longer string) | Yes |
| Formal standard | RFC 9562 / RFC 4122 | Community library |
| Native DB type | Yes (PostgreSQL, MySQL 8+) | No (VARCHAR/TEXT) |
| JS bundle size | 0 (native crypto.randomUUID) | ~130 bytes gzipped |
| Time-sortable | No (use UUID v7) | No |
Length and storage
A UUID v4 is always 36 characters when displayed with hyphens (32 hex digits + 4 hyphens). NanoID defaults to 21 characters. The shorter form reduces storage in indexes, logs, URLs and JSON payloads. In high-volume tables or when IDs appear in every API response, the difference is measurable.
NanoID also lets you change the length. Shorter IDs lower entropy; longer ones raise it. The default 21-character setting was chosen to match or slightly exceed the collision resistance of UUID v4.
Collision probability
UUID v4 has 122 bits of randomness. NanoID’s default alphabet (64 characters) and length (21) yield approximately 126 bits. In both cases the probability of a random collision is negligible for any realistic system.
You would need to generate on the order of 10¹⁸ identifiers before the birthday-paradox risk becomes material. For almost all applications the difference in raw entropy is irrelevant; practical concerns (length, URL safety, library support) matter more.
URL safety and public identifiers
NanoID uses only characters that are safe in URLs and file names (A-Z, a-z, 0-9, _, -). A UUID contains hyphens; while hyphens are allowed in URLs, the longer string is less convenient for short links, invite codes or path segments.
If the identifier will appear in a public URL, a QR code, or a shareable token, NanoID is usually the cleaner choice.
Standards and interoperability
UUID is an official standard (RFC 4122, updated by RFC 9562). Every major language, database and cloud service understands it. PostgreSQL and recent MySQL versions offer a native UUID column type, which can be more efficient than a string column for indexing and storage.
NanoID is a library specification. Ports exist for many languages, but it is not a formal standard. Systems that must exchange identifiers with third parties, older systems, or multiple language stacks generally prefer UUID.
Generation speed and bundle size
In modern browsers and Node.js, crypto.randomUUID() is built-in and requires no extra dependency. The popular uuid package is larger. NanoID’s JavaScript implementation is extremely small (~130 bytes gzipped) and benchmarks show it is competitive with, or faster than, common UUID libraries.
For pure client-side applications where every byte counts, NanoID has a measurable advantage. On the server the difference is rarely decisive.
Database primary keys
Both formats can serve as primary keys. UUID benefits from native type support in several databases. Random UUIDs (v4) and random NanoIDs both produce non-sequential values, which can cause index fragmentation on large, write-heavy tables. If index locality matters, consider time-sortable alternatives such as UUID v7 or ULID instead of either UUID v4 or NanoID.
Practical recommendations
Prefer UUID v4 when:
- identifiers cross system or language boundaries
- you need a formal standard or native database UUID type
- the project already standardises on UUIDs
Prefer NanoID when:
- identifiers appear in URLs, tokens or short codes
- you control both ends of the system and mainly work in JavaScript/TypeScript
- shorter strings or a tiny client-side library are valuable
Many codebases use both: UUID for internal primary keys and NanoID for public-facing tokens and slugs.
Try them
You can generate both formats directly in the browser with no data leaving your device: