Number of UUIDs

Format options

With hyphens (xxxxxxxx-xxxx-...)

Uppercase

Generate UUIDs Clear

? Generate 1 ? Generate 5 ? Generate 10 ? Toggle hyphens ? Toggle uppercase

What is a GUID / UUID?

A Globally Unique Identifier (GUID) or Universally Unique Identifier (UUID) is a 128‑bit number used to uniquely identify information in computer systems. The standard is defined by RFC 4122 (IETF) and ISO/IEC 9834‑8:2014. The most common representation is a 36‑character string of hexadecimal digits, grouped as xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.

Version 4 UUIDs are generated from random or pseudo‑random numbers. They provide high entropy (122 random bits) and do not require any central coordination, MAC addresses, or timestamps, making them ideal for distributed environments.

Why Version 4 Random UUIDs?

• No central authority – every node can generate its own IDs without coordination.
• Cryptographically secure – when backed by a CSPRNG (like crypto.getRandomValues), UUIDs are unpredictable and suitable for security tokens.
• Standardized – universally accepted by databases (PostgreSQL, MySQL, SQL Server), programming languages, and APIs.
• Fast generation – millions per second on modern hardware.

UUID Version Comparison

Version	Generation method	Characteristics	Typical use
v1 (time‑based)	Timestamp + MAC address / node	Time‑ordered, but may leak host info	Legacy systems, approximate ordering (not recommended for security)
v3 / v5 (name‑based)	MD5 (v3) or SHA‑1 (v5) of namespace + name	Deterministic: same input yields same UUID	Generating fixed IDs from domain names, URLs, etc.
v4 (random)	122 random bits + fixed version/variant	High entropy, no information leakage, no coordination	Primary keys, session IDs, random identifiers, distributed systems
v6‑v8 (draft)	Time‑ordered random (v7) or custom	Future standards combining time and randomness	Database‑friendly ordered UUIDs (v7), experimental use (v8)

Real‑World Application: Distributed Primary Keys

Collision Probability – How Small Is It Really?

With 122 random bits, the chance of a collision among N UUIDs is approximately N² / (2 * 2¹²²) (birthday problem). Even after generating 1 billion UUIDs per second for 100 years, the probability of a single collision remains below 10⁻¹². For practical purposes, you can treat v4 UUIDs as unique.

Cryptographic Security & Entropy Sources

This tool exclusively uses window.crypto.getRandomValues(), a CSPRNG (Cryptographically Secure Pseudo‑Random Number Generator) backed by the operating system’s entropy pool (e.g., /dev/urandom on Linux, CryptGenRandom on Windows). This ensures that the generated UUIDs are suitable for security‑sensitive applications such as password reset tokens, API keys, and session identifiers.

Common Misconceptions (Cleared)

• “UUIDs are 100% guaranteed unique.” No, but the probability of collision is so low that they are considered unique for all practical purposes.
• “GUID and UUID are different.” Microsoft historically used “GUID” but both refer to the same 128‑bit identifier; most GUIDs are RFC 4122 compliant.
• “UUID v4 slows down databases due to randomness.” Random UUIDs can cause index fragmentation in B‑trees, but modern databases handle it well; for write‑heavy systems, consider UUID v7 (time‑ordered) when it stabilizes.
• “Any random function (Math.random) is enough for UUID.” Math.random() is not cryptographically secure and has lower entropy; always use a CSPRNG for UUID generation in production.

Technical Implementation & RFC Compliance

Our generator strictly follows RFC 4122 section 4.4 (“Algorithms for Creating a UUID from Truly Random or Pseudo‑Random Numbers”). We obtain 16 random bytes, then set the version (bits 48‑51 of the UUID) to 0b0100 (byte index 6, high nibble = 4) and the variant (bits 64‑65) to 0b10 (byte index 8, high two bits = 10). The code is open for inspection and uses only standard Web APIs.

Performance & Scalability

Generating 10,000 UUIDs with this tool takes less than 100ms on a typical laptop. For server‑side generation, the same JavaScript can be used in Node.js (via crypto.randomUUID() or crypto.randomBytes()). The algorithm is linear and memory‑efficient.

Future: UUIDv6, v7, v8

The IETF is currently working on an update to RFC 4122 (draft‑uuidrev) that introduces new versions: v6 (reordered v1), v7 (time‑ordered random, great for databases), and v8 (custom). GetZenQuery will offer v7 generators once the specification is final. Meanwhile, v4 remains the most widely supported and secure choice.

Frequently Asked Questions