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

Primary keys and public IDs show up everywhere: database rows, API resources, file names, and idempotency keys. UUID, Nano ID, and ULID all solve “give me a unique string,” but they trade size, readability, and sortability differently. Pick the format that matches how you store and query — then generate samples on FileToolsHub without installing a package.

What each format is

UUID (Universally Unique Identifier) is the classic 128-bit ID, usually shown as 36 characters with hyphens (version 4 is random). Libraries exist in every language. Nano ID is a smaller, URL-friendly random ID tuned for web apps — shorter strings, custom alphabets, and less visual noise than UUID. ULID (Universally Unique Lexicographically Sortable Identifier) encodes a timestamp in the high bits so IDs sort roughly by creation time when compared as strings.

UUID v7 is the modern UUID variant that also embeds a Unix timestamp — similar motivation to ULID, but in UUID shape for ecosystems that already expect UUID columns and types.

Size and readability comparison

UUID v4 text form is long and hyphenated — fine in databases, awkward in URLs and support tickets. Nano ID defaults are shorter and use an alphabet that avoids ambiguous characters, which helps when humans copy IDs from logs. ULID is 26 characters of Crockford’s Base32: compact, case-insensitive friendly, and still random enough for uniqueness at practical scales.

If operators read IDs aloud or paste them into chats, shorter and unambiguous beats “RFC purity.” If your ORM and migrations already standardize on UUID, staying in the UUID family (including v7) often costs less than introducing a second ID type.

Sortability (ULID's key advantage)

Random UUID v4 values do not sort by time. Inserts scatter across B-tree indexes and make “roughly chronological” listing harder without a separate created_at column. ULID and UUID v7 put time in the leading bits so lexicographic order approximates creation order — useful for event logs, feed-style tables, and pagination that wants newest-ish clustering.

Sortability is not a full substitute for a real timestamp column when you need exact auditing, but it reduces index fragmentation versus pure random IDs and makes raw ID lists easier to skim.

When to use which

Use UUID v4 when interoperability and ubiquity matter more than length — existing schemas, external systems that validate UUID format, or teams that already standardized on it. Use UUID v7 when you want UUID compatibility plus time-ordered IDs. Use Nano ID for public URLs, share links, and UI-facing tokens where shorter strings improve UX. Use ULID when string-sortable time-ordered IDs matter and you are fine adopting ULID libraries end to end.

Avoid putting secrets in any of these: uniqueness is not confidentiality. For API keys and passwords, use dedicated generators instead.

Try each generator

Generate samples in the browser: /tool/uuid-generator, /tool/nanoid-generator, /tool/ulid-generator, and /tool/uuid-v7-generator. Nothing uploads — copy a few values into your design doc or migration notes and decide with real strings in hand.