UUID & GUID Generator
Generate cryptographically secure Universally Unique Identifiers (UUIDs / GUIDs) conforming to RFC 4122 and RFC 9562. Supports bulk generation for UUID v4 (random), UUID v7 (time-ordered Unix epoch), UUID v1 (timestamp), and includes a real-time UUID inspector and timestamp decoder.
How to use
Select your target UUID version: Version 4 (cryptographically random), Version 7 (time-ordered for databases), or Version 1 (timestamp-based).
Choose your desired output quantity (1 to 1000 UUIDs).
Configure formatting options: uppercase/lowercase, hyphens, curly braces, quotes, or array wrappers.
Click Generate to produce fresh identifiers using your browser's CSPRNG.
Copy individual values, export all as text or JSON, or paste an existing UUID into the Inspector tab to decode its version, variant, and embedded timestamp.
Understanding Universally Unique Identifiers (UUID)
A Universally Unique Identifier (UUID), also known in Microsoft environments as a Globally Unique Identifier (GUID), is a 128-bit value standardized by the Internet Engineering Task Force (IETF) in RFC 4122 and updated in RFC 9562. UUIDs enable distributed systems to generate unique identifiers without requiring central coordination or database locks.
UUID version comparison
| Version | Standard | Generation Mechanism | Primary Use Case |
|---|---|---|---|
| UUID v4 | RFC 4122 / RFC 9562 | 122 bits of pseudo-random entropy generated via a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG). | General purpose distributed entity IDs, API request tracking, and session tokens. |
| UUID v7 | RFC 9562 | 48-bit Unix timestamp (millisecond precision) combined with 74 bits of sub-millisecond precision and random entropy. | Database primary keys and B-tree indexes where sequential locality prevents index fragmentation. |
| UUID v1 | RFC 4122 | 60-bit Gregorian timestamp (100-nanosecond intervals since Oct 15, 1582) combined with clock sequence and node/MAC address. | Legacy distributed systems requiring strict chronological sorting. |
| UUID v5 | RFC 4122 | SHA-1 cryptographic hash of a namespace UUID and an arbitrary string identifier. | Deterministic identification (e.g., mapping URLs or DNS names to consistent UUIDs). |
| Nil / Max | RFC 4122 / RFC 9562 | All 128 bits set to 0 (00000000-0000-0000-0000-000000000000) or all bits set to 1. | Null pointer placeholders, uninitialized values, or range sentinel bounds. |
Anatomy of a standard UUID string
A canonical UUID is represented as 32 hexadecimal digits displayed in 5 hyphen-separated groups: 8-4-4-4-12 (e.g., xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx). Two critical nibbles define the UUID metadata:
- Version (M): The first digit of the third group indicates the version number (e.g.,
4for v4 random,7for v7 time-ordered,1for v1). - Variant (N): The high bits of the fourth group denote the variant. Under RFC 4122 and RFC 9562, bits
10xxindicate the standard variant, meaning the characterNis always one of8,9,a, orb.
Database performance: Why UUID v7 replaces UUID v4 for primary keys
While UUID v4 provides random distribution, inserting random keys into clustered B-Tree indexes (such as PostgreSQL PRIMARY KEY or MySQL InnoDB clustered indexes) causes heavy page splits, random disk I/O, and index fragmentation. UUID v7 solves this by placing a 48-bit Unix millisecond timestamp at the beginning of the identifier. As a result, new keys append monotonically to the end of index leaf pages, reducing write amplification and improving cache hit ratios while preserving global uniqueness across distributed servers.
Client-side cryptographic security
All UUID generation on this site uses the native browser Web Crypto API (globalThis.crypto.getRandomValues) to source hardware-backed entropy from the operating system kernel. No identifiers are generated on or transmitted to external servers, ensuring that tokens, keys, and identifiers remain strictly confidential within your browser.
Frequently asked questions
What is the probability of a collision in UUID v4?
UUID v4 provides 122 bits of random entropy (2^122 or approximately 5.3 x 10^36 possible values). To have a 50% probability of finding a single duplicate collision, an application would need to generate approximately 2.71 quintillion UUIDs.
What is the difference between UUID and GUID?
UUID (Universally Unique Identifier) is the standard term defined in IETF RFC 4122 and RFC 9562. GUID (Globally Unique Identifier) is Microsoft's implementation term. Both represent 128-bit values and follow identical structural layouts.
Why should I use UUID v7 instead of UUID v4 for database primary keys?
UUID v7 starts with a 48-bit Unix epoch millisecond timestamp, making newly generated IDs naturally sorted chronologically. This prevents B-Tree index fragmentation and improves database insert throughput compared to completely random UUID v4.
Can I extract the creation timestamp from a UUID?
Yes, for UUID v1 and UUID v7. Our built-in UUID Inspector automatically decodes the embedded 48-bit Unix timestamp from UUID v7 and Gregorian timestamp from UUID v1 to display the exact date and millisecond time.
Are the generated UUIDs sent to a server or stored?
No. All UUIDs are generated directly in your browser using the client-side Web Crypto API. No generated values or inspected strings are transmitted across the network.