Table of Contents
Three identifiers, three trade-offs
| UUID v1 | UUID v4 | ULID | |
|---|---|---|---|
| Layout | timestamp + MAC | random | millisecond time + random |
| Sortable by time | Yes (but leaks MAC) | No | Yes |
| Privacy | Weak (MAC exposed) | Strong | Medium (time only) |
| Alphabet | hex + - | hex + - | Crockford Base32 |
UUID v1
Built from a timestamp and the node’s MAC address. It sorts and is unique without a coordinator, but the MAC is a privacy leak and the time reveals when you created the ID.
UUID v4
Pure random (122 bits). No ordering, no leakage — the safe default when you just need a unique token and do not care about sort order.
f47ac10b-58cc-4372-a567-0e02b2c3d479 (v4)UUID v7 / v8
Newer time-ordered UUIDs that keep v4’s privacy story while sorting like ULID. If your stack supports them, they are a great middle ground.
ULID
ULID leads with a millisecond timestamp in Base32, so string sorting equals chronological order — perfect as a database primary key where you want inserts to land in time order.
01ARZ3NDEKTSV4RRFFQ69G5FAV (timestamp | randomness)The catch: 26 chars in Crockford Base32, so it is not drop-in compatible with UUID columns expecting 36-char hex.
When to pick which
- Random opaque token: UUID v4.
- Sortable DB primary key: ULID or UUID v7.
- Avoid v1 unless you specifically need MAC-based uniqueness and accept the leak.
Generate them
Related tools
- UUID Generator on Toolbox
- ULID Generator on Toolbox
- UUID Generator on Toolhub
- UUID Generator on DevTools
Next steps
- Wallet keys use a different scheme — see BIP39 Derivation Path.
- Time values themselves need care — Unix Timestamp: 10 vs 13 digits.
Frequently asked questions
Is a UUID v4 guaranteed unique?
Not mathematically, but the 122-bit random space is so large that collisions are astronomically unlikely in practice. Uniqueness comes from randomness, not from a central authority.
Why avoid UUID v1?
v1 embeds the MAC address and a timestamp, which can fingerprint a machine and reveal creation time. Prefer v4 (random) or v7/v8 (time-ordered) for privacy.
What makes ULID sortable?
ULID puts a millisecond timestamp first, encoded in Crockford Base32, so lexicographic order matches creation time — handy as a primary key in a database.
Guide Info
- Category
- Explained
- Difficulty
- Beginner
- Reading Time
- 2 min
- Tags
- #uuid #ulid #identifier #generator
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