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UUID Generator

Generate cryptographically secure UUID v4 identifiers — one at a time or up to 50 in a single click.

      550e8400-e29b-41d4-a716-446655440000
    

Version 4 · Random CSPRNG · random_bytes() 1–50 per request

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Anatomy of a UUID v4

128 bits, 32 hex characters, 5 groups — two of which carry version and variant flags.

      550e8400-e29b-41d4-a716-446655440000
    

8 hex chars

Random bits (32)

4 hex chars

Random bits (16)

"4" prefix

Version 4 marker

3 hex chars

Random bits (12)

"a"–"b" prefix

Variant bits (RFC 4122)

2 hex chars

Random bits (14)

12 hex chars

Random bits (48)

122 of the 128 bits are random — the remaining 6 encode the version (4) and variant (RFC 4122).

UUID versions compared

v4 is the right choice for most applications — here's why.

Version	Method	Sortable	Privacy	Use when
v1	Time + MAC address	✓	✗ Leaks MAC	Legacy systems only
v3	MD5 name-based	—	✓	Deterministic IDs from a namespace + name (legacy)
v4 ★	Random (CSPRNG)	✗	✓	General purpose — most common choice
v5	SHA-1 name-based	—	✓	Deterministic IDs from a namespace + name
v7	Time-ordered random	✓	✓	DB primary keys (no fragmentation) — emerging standard

Where to use UUIDs

🗄️

Database primary keys

Generate IDs client-side before inserting — no round-trip to the DB needed. Works across distributed systems without a central sequence.

🔗

API resource identifiers

Expose UUIDs in REST URLs instead of sequential integers — prevents enumeration attacks and decouples external IDs from internal auto-increment keys.

📁

File and upload naming

Rename user-uploaded files to a UUID to avoid path traversal, conflicts and directory disclosure of original filenames.

🔐

Session and token IDs

Use UUIDs for session identifiers, invite tokens, password reset links and one-time codes — large random space makes brute-force infeasible.

📊

Event and log correlation

Attach a UUID to every request or event at the entry point. Propagate it through microservices to correlate all log entries for a single operation.

🧪

Test data generation

Generate unique IDs for fixtures and seed data without conflicts — especially useful when seeding across multiple environments simultaneously.

Frequently asked questions

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 32 hexadecimal characters in five groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. They are designed to be globally unique without a central coordinator.

What is the difference between UUID v4 and other versions?

UUID v1 is time-based and includes the MAC address — a privacy risk. UUID v3 and v5 are name-based (MD5 and SHA-1) and deterministic. UUID v4 is randomly generated using a CSPRNG and the most widely used version — no embedded metadata and collisions are astronomically unlikely.

How unique is a UUID v4?

A UUID v4 has 122 random bits. The probability of a collision among 1 billion UUIDs generated per second for 100 years is roughly 50% — meaning in any realistic application, duplicates are negligible.

Should I use UUIDs as database primary keys?

UUIDs work well when you need client-side ID generation, cross-system uniqueness, or want to avoid exposing sequential integers. The trade-off is B-tree index fragmentation (random inserts) and 16 bytes vs 4–8 for integers. UUID v7 (time-ordered) solves fragmentation but is not yet widely supported.

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