A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 32 hexadecimal digits in 5 groups separated by hyphens: 8-4-4-4-12 (e.g., 550e8400-e29b-11d4-a716-446655440000). UUIDs are designed to be unique across space and time without a central authority. They are also known as GUIDs (Globally Unique Identifiers) in Microsoft ecosystems.

What is the difference between UUID versions?

Version 1 uses timestamp + MAC address. Version 3 uses MD5 hash of a namespace+name (deterministic). Version 4 uses 122 random bits (most common today). Version 5 uses SHA-1 hash of namespace+name (preferred over v3). Version 7 (newest) uses Unix timestamp + random bits and is time-sortable, making it ideal for database primary keys.

Which UUID version should I use?

For most applications, use UUID v4 (random) — it is simple, has no privacy concerns, and has an astronomically low collision probability. For database primary keys where sort order matters, use UUID v7 (time-based, sortable). For deterministic IDs derived from a name (like generating the same UUID from the same email), use UUID v5.

Can UUID v1 reveal my MAC address?

Yes. UUID v1 embeds the generating machine MAC address in the last 12 hex digits (node field). This is why v1 is considered a privacy concern and why v4 (random) is preferred in most applications. Some implementations use a random node ID instead of the real MAC address to mitigate this.

The nil UUID is 00000000-0000-0000-0000-000000000000 (all zeros). It is a special UUID defined in RFC 4122 that represents the absence of a value, similar to null. It is useful as a default or placeholder value in databases and APIs where a UUID field is required but no real UUID exists yet.

How many UUIDs can be generated before a collision?

UUID v4 has 122 random bits, giving 2^122 (about 5.3 x 10^36) possible values. To have a 50% probability of at least one collision, you would need to generate about 2.7 x 10^18 (2.7 quintillion) UUIDs. At 1 billion UUIDs per second, that would take about 85 years. For practical purposes, collisions are negligible.

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UUID Validator & Analyzer

A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 32 hexadecimal digits in 5 groups: 8-4-4-4-12. Version is encoded in the 13th character: v1 (timestamp), v4 (random), v7 (Unix timestamp + random). The variant field (character 17) indicates RFC 4122 compliance. Nil UUID is all zeros. Valid UUIDs match the pattern [0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}.

Validate and analyze UUIDs (GUIDs). Check if a UUID is valid, identify its version (v1-v8), variant, and extract embedded data like timestamps. Generate random v4 UUIDs. Supports all UUID versions including v7.

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Presets

UUID Input

UUID Version Reference

Version	Type	Description
Nil	00000000-...	All zeros, represents absence of UUID
1	Time-based	Timestamp (60-bit) + clock sequence + MAC address
2	DCE Security	Like v1 but with POSIX UID/GID. Rarely used
3	Name (MD5)	MD5 hash of namespace + name. Deterministic
4	Random	122 random bits. Most commonly used today
5	Name (SHA-1)	SHA-1 hash of namespace + name. Preferred over v3
6	Reordered Time	Like v1 but time bits are sortable (draft RFC)
7	Unix Time	Unix timestamp (ms) + random. Sortable, modern
8	Custom	Vendor-defined format. Application-specific

How to Use

1
Enter a UUID
Paste a UUID string (with or without hyphens, 32 or 36 characters). Or click a preset to analyze sample UUIDs of different versions.
2
View validation results
See if the UUID is valid, its version (v1-v8), variant (RFC 4122, Microsoft, NCS), and formatted representations (standard, no hyphens, URN).
3
Check embedded data
For v1 UUIDs, see the embedded timestamp. For nil/max UUIDs, see special status. Version and variant bits are decoded automatically.
4
Generate or copy
Click Generate v4 to create a random UUID. Click Copy to copy the formatted UUID for use in your application.

Frequently Asked Questions

What is a UUID?: A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 32 hexadecimal digits in 5 groups separated by hyphens: 8-4-4-4-12 (e.g., 550e8400-e29b-11d4-a716-446655440000). UUIDs are designed to be unique across space and time without a central authority. They are also known as GUIDs (Globally Unique Identifiers) in Microsoft ecosystems.
What is the difference between UUID versions?: Version 1 uses timestamp + MAC address. Version 3 uses MD5 hash of a namespace+name (deterministic). Version 4 uses 122 random bits (most common today). Version 5 uses SHA-1 hash of namespace+name (preferred over v3). Version 7 (newest) uses Unix timestamp + random bits and is time-sortable, making it ideal for database primary keys.
Which UUID version should I use?: For most applications, use UUID v4 (random) — it is simple, has no privacy concerns, and has an astronomically low collision probability. For database primary keys where sort order matters, use UUID v7 (time-based, sortable). For deterministic IDs derived from a name (like generating the same UUID from the same email), use UUID v5.
Can UUID v1 reveal my MAC address?: Yes. UUID v1 embeds the generating machine MAC address in the last 12 hex digits (node field). This is why v1 is considered a privacy concern and why v4 (random) is preferred in most applications. Some implementations use a random node ID instead of the real MAC address to mitigate this.
What is a nil UUID?: The nil UUID is 00000000-0000-0000-0000-000000000000 (all zeros). It is a special UUID defined in RFC 4122 that represents the absence of a value, similar to null. It is useful as a default or placeholder value in databases and APIs where a UUID field is required but no real UUID exists yet.
How many UUIDs can be generated before a collision?: UUID v4 has 122 random bits, giving 2^122 (about 5.3 x 10^36) possible values. To have a 50% probability of at least one collision, you would need to generate about 2.7 x 10^18 (2.7 quintillion) UUIDs. At 1 billion UUIDs per second, that would take about 85 years. For practical purposes, collisions are negligible.