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Choose a UUID version to generate identifiers, or inspect an existing UUID.
What Is a UUID / GUID Generator?
A UUID / GUID Generator creates 128-bit identifiers used in databases, APIs, distributed systems, event streams, test fixtures, and software configuration. UUID means Universally Unique Identifier. GUID is Microsoft's widely used name for the same general 128-bit identifier format.
The familiar canonical representation uses 32 hexadecimal characters divided into five groups: 8-4-4-4-12. A UUID contains version and variant bits that explain how it was generated. This tool follows RFC 9562, generates secure random values server-side, and can inspect an existing UUID without storing it.
UUIDs are designed to make collisions extraordinarily unlikely or to create repeatable names, depending on the version. They are identifiers rather than secrets. A UUID should never replace a password, authorization check, API key, or secure session token.
UUID v4 vs UUID v7 vs UUID v5
Choose a UUID version based on whether you need random identifiers, approximate creation-time ordering, or deterministic repeatable identifiers.
| Version | Source | Time Sortable | Deterministic | Common Use |
|---|---|---|---|---|
| UUID v4 | 122 secure random bits | No | No | General IDs and test data |
| UUID v7 | Unix milliseconds plus random bits | Yes, by millisecond | No | Database and event IDs |
| UUID v5 | Namespace and exact name | No | Yes | Stable repeatable IDs |
Are UUIDs Really Unique?
No finite identifier can provide a mathematical guarantee of global uniqueness. A correctly generated UUID v4 has 122 random bits, making accidental collision probability extraordinarily small in practical applications.
The quality of the random source matters. This generator uses Go's crypto/rand, which reads from the operating system's cryptographically secure random source. It never falls back to predictable pseudo-random numbers.
Using UUIDs as Database Keys
UUID v4 works well when identifiers must be generated independently without coordinating a central sequence. Random insertion order can cause less-localized index writes in some databases, so performance should be measured with the actual database and workload.
UUID v7 places Unix milliseconds at the beginning, allowing values to sort approximately by creation time. This can improve index locality while retaining random bits, but identifiers created within the same millisecond are not guaranteed to preserve exact generation order.
UUID Formats and GUID Compatibility
The canonical lowercase format is the most portable representation: 550e8400-e29b-41d4-a716-446655440000. Uppercase hexadecimal represents the same 128-bit value. Compact UUIDs remove hyphens, braced GUIDs add curly braces, and UUID URNs add the urn:uuid: prefix.
When exchanging UUIDs between systems, prefer the canonical format unless an API or database explicitly requires another representation. The inspector accepts all formats supported by this generator and normalizes them without silently removing arbitrary punctuation.
UUID v5 treats the name as exact UTF-8 bytes. Capitalization, spaces, line endings, and Unicode composition can change the derived UUID. The same namespace and exact name always produce the same value.
UUID Security Limitations
A UUID may be difficult to guess, but unpredictability alone is not authorization. Applications must still verify that the authenticated user is allowed to access the record identified by a UUID. Exposing a UUID should not grant permission automatically.
UUID v7 intentionally exposes a millisecond creation timestamp. Use UUID v4 when revealing approximate creation time is undesirable. UUID v5 is fully deterministic, so anyone who knows the namespace and name can reproduce it. None of these versions should be treated as secret credentials.
UUID / GUID Generator FAQs
What is the difference between UUID and GUID?
UUID is the standards-oriented term for a 128-bit universally unique identifier. GUID is Microsoft's common term and often appears in Windows, .NET, SQL Server, and related tooling; canonical UUID and GUID text usually represent the same type of value.
Is UUID v4 guaranteed to be unique?
No UUID version can guarantee uniqueness across unlimited generation. UUID v4 uses enough secure random bits that collisions are extraordinarily unlikely, but applications with strict requirements can still enforce a unique database constraint.
Should I use UUID v4 or UUID v7?
Use UUID v4 when you need a broadly supported random identifier and do not need time ordering. Consider UUID v7 when approximate creation-time sorting and database index locality are useful, while remembering that it exposes a timestamp.
Can a UUID reveal when it was created?
UUID v7 directly stores a Unix-millisecond timestamp that this inspector can display. UUID v4 and UUID v5 do not contain a standardized creation timestamp, so one should not be inferred from those versions.
Can I use a UUID as an API key?
No. UUIDs are identifiers, not authentication secrets, and applications must not rely on possession of a UUID as proof of authorization. Use purpose-built, revocable credentials with sufficient entropy and enforce access control independently.
Why does UUID v5 always generate the same value?
UUID v5 hashes a namespace UUID together with exact name bytes, then sets the standard version and variant bits. This deterministic behavior is useful when multiple systems need to derive the same stable identifier without sharing stored state.
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