Nano ID vs UUID: Which Unique ID Should You Use?

Every record, file and short link needs an identifier, and the default choice for years has been the UUID. Then Nano ID came along with a shorter, URL-friendly format and a similar safety margin, and many teams started asking whether they should switch. The honest answer depends on where your IDs live and who sees them. This comparison explains how both formats work and when each one is the better fit.

Two formats side by side

A random UUID version 4 looks like 3f2b8c1e-9d4a-4f6b-8a2e-7c5d1b0e9f34: 36 characters, hexadecimal digits and four hyphens. Six of its 128 bits are fixed to mark the version and variant, leaving 122 random bits.

A Nano ID in its original form looks like V1StGXR8_Z5jdHi6B-myT: 21 characters drawn from a 64-symbol alphabet of letters, digits, underscore and hyphen. Each character carries 6 bits, so 21 characters give 126 random bits — slightly more than a UUID in about 40% fewer characters.

Collision risk in plain terms

Random IDs can collide only by chance. Thanks to the “birthday problem”, the risk starts to matter once you have generated roughly 2 to the power of half the bit count — around 2⁶¹ for a UUID or default Nano ID. That is billions of IDs per second for many years, far beyond almost any application.

Shortening a Nano ID changes the picture quickly. Each character you remove takes away 6 bits, so a 10-character ID has 60 bits and should only be used where the total number of IDs stays modest and a rare collision can be detected and retried — for example by a unique constraint in the database.

Where each format fits best

• Choose UUID when databases, ORMs or external systems expect it, when you want a native uuid column type, or when your team values a universally recognized standard.
• Choose Nano ID for public-facing IDs in URLs, short links, file names and invite codes, where compactness and a URL-safe alphabet matter.
• Consider a time-ordered ID such as a ULID when records are inserted at high volume and you want them to sort by creation time.

Many systems use both: an internal key for the database and a short public ID for URLs, so internal numbering is never exposed.

How to generate Nano IDs with the tool

The generator above creates Nano ID-style identifiers with the Web Crypto API in your browser:

1. Keep the default length of 21 for general-purpose unique IDs, or set any value from 4 to 64.
2. Use shorter lengths only for human-facing codes in small systems, and longer ones when you want an extra safety margin.
3. Generate up to 200 IDs at once — enough to seed a test table or a batch of invite links.
4. Copy the list or export it as CSV, JSON or TXT.

The IDs are never sent to a server, so they are safe to use as real identifiers.

Practical tips for storing short IDs

Nano IDs are case-sensitive, so store them in a column with a case-sensitive collation; otherwise abc and ABC may be treated as the same value. Add a unique index regardless of the format, so the database rejects the astronomically rare duplicate instead of silently accepting it. And if people will read IDs aloud, consider a custom alphabet without look-alike characters such as 0 and O.

Choosing a length for short IDs

If you shorten Nano IDs, size them for the number of IDs you will ever create, not for today’s traffic. A rough guide with the 64-symbol alphabet:

• 8 characters (48 bits) — fine for a few thousand items such as invite codes, with a uniqueness check.
• 12 characters (72 bits) — comfortable for millions of records.
• 21 characters (126 bits) — the default, safe for practically any scale.

When in doubt, go longer. A few extra characters in a URL cost almost nothing; a collision in production can cost a lot.

Pro tips

• Default to 21 characters unless you have a specific reason to go shorter.
• Always add a unique constraint to ID columns.
• Keep internal database keys and public URL IDs separate when possible.
• Check case-sensitivity of your database before storing mixed-case IDs.

Frequently asked questions