UUID Generator

About UUIDs

A UUID (Universally Unique Identifier) is a 128-bit value used to identify information uniquely across distributed systems without coordination. The probability of generating two identical UUIDs is so low that they can be safely treated as unique in practice.

UUID v4 — random

UUID v4 is generated entirely from random bits (with 6 bits reserved for version and variant markers). It produces unpredictable, unguessable identifiers — ideal for security tokens, session IDs, and any case where you want collision resistance without leaking generation order.

UUID v7 — timestamp-ordered

UUID v7, standardized in RFC 9562 (2024), embeds a Unix millisecond timestamp in the leading 48 bits, followed by random bits. Because the high-order bits monotonically increase with time, v7 UUIDs sort naturally by creation order. This makes them dramatically better as database primary keys: B-tree indexes stay locality-friendly, and inserts cluster at the end of the index instead of fragmenting it like v4.

When to use which

• v4: API keys, session tokens, public-facing IDs, anything where order should not be inferable
• v7: Database primary keys, distributed event logs, anything benefiting from time ordering

Formatting options

The standard form uses 8-4-4-4-12 hexadecimal digits separated by hyphens. The no-hyphens form (32 contiguous hex characters) is common in URL paths and filenames. Uppercase is sometimes required by legacy systems. The braces form ({xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}) is the canonical Microsoft / C# representation.