> uuid | guid | generate <
// Generate universally unique identifiers (UUID/GUID) instantly
Cryptographic Random
UUID v4 uses crypto.getRandomValues() for cryptographically secure random generation. Your data never leaves your browser.
Batch Generation
Generate up to 100 UUIDs at once. Perfect for database seeding, testing, and development workflows.
Multiple Versions
Support for UUID v4 (random) and v1 (timestamp-based). Choose the version that fits your use case.
// ABOUT UUID GENERATION
How UUID Works:
UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. UUID v4 uses 122 random bits providing 2^122 possible values. The 36-character format follows the 8-4-4-4-12 pattern with version and variant bits embedded.
Example:
550e8400-e29b-41d4-a716-446655440000
Common Use Cases:
- >Database primary keys and record identifiers
- >Distributed systems without central coordination
- >Session tokens and correlation IDs
- >File naming and resource identification
- >API request tracing and logging
>> frequently asked questions
Q: What is a GUID?
A: A GUID (Globally Unique Identifier) is a 128-bit number used to uniquely identify information across systems without a central authority. The term GUID originated with Microsoft's COM/DCOM and remains the standard term in .NET, Windows, SQL Server, and Active Directory. Structurally, a GUID is identical to a UUID: 32 hexadecimal characters formatted as 8-4-4-4-12 with hyphens (e.g., 550e8400-e29b-41d4-a716-446655440000).
Q: What is a UUID?
A: A UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. It is also known as GUID (Globally Unique Identifier). The standard format is 8-4-4-4-12 hexadecimal characters separated by hyphens.
Q: What is the difference between GUID and UUID?
A: GUID and UUID are the same 128-bit identifier format with two different names. UUID is the term defined by the IETF (RFC 4122) and used across most open-source and cross-platform ecosystems. GUID is the term Microsoft chose for the same concept and is used throughout Windows, .NET, SQL Server, Azure, and COM. A GUID you generate in C# is fully interoperable with a UUID generated in Java or Python — same bits, same format, different name.
Q: How do I generate a GUID online?
A: Use the [GENERATE] button above. Pick a version (v4 random for most use cases, v1 timestamp-based if you need a chronological component), choose uppercase or lowercase, and set how many you want — you can bulk generate up to 100 at once. The GUIDs are created locally in your browser using the Web Crypto API; nothing is sent to any server.
Q: How do I generate a GUID in code?
A: Every major platform has a built-in generator:
C# / .NET — Guid.NewGuid()
PowerShell — [guid]::NewGuid()
JavaScript (modern) — crypto.randomUUID()
Python — uuid.uuid4()
Java — UUID.randomUUID()
Go — uuid.New() from google/uuid
SQL Server — NEWID()
PostgreSQL — gen_random_uuid()
Q: What is the difference between UUID v1, v4, and v7?
A: v1 is time-based: it encodes the current timestamp and a MAC/node identifier. Useful when you need chronological sortability but it leaks information about when and where the ID was generated. v4 is fully random (122 random bits). It is the most widely used version because it is simple, private, and collision-resistant. v7 (RFC 9562, published 2024) combines both: it starts with a 48-bit Unix timestamp in milliseconds, then fills the remaining bits with randomness. v7 is becoming the recommended choice for database primary keys because it sorts by creation time while still being globally unique.
Q: What is the probability of GUID collision?
A: GUID/UUID v4 has 122 random bits, giving 2^122 (approximately 5.3 × 10^36) possible values. The probability of generating a duplicate is astronomically low — you would need to generate about 2.71 quintillion (2.71 × 10^18) GUIDs to have a 50% chance of a single collision. For practical purposes, every GUID you generate is unique forever across every machine in the world.
Q: Are GUIDs case-sensitive?
A: The hexadecimal characters in a GUID are case-insensitive — 550E8400-E29B-41D4-A716-446655440000 and 550e8400-e29b-41d4-a716-446655440000 represent the same identifier. However, different systems display them differently by convention: Microsoft tools typically use uppercase, while Linux/macOS and most web frameworks use lowercase. When storing GUIDs as strings in a database, always normalize the case to avoid duplicate-looking but logically identical keys.
Q: Should I use GUID as a database primary key?
A: It depends on your workload. Pros: GUIDs can be generated on the client, distributed systems don't need to coordinate, and there's no predictable sequence to enumerate. Cons: Random GUIDs (v4) fragment B-tree indexes and waste more storage than 32-bit auto-increment integers. If you need a GUID primary key on a heavily-written table, use UUID v7 or a sequential GUID (COMB GUID) — these preserve insertion locality and dramatically improve index performance.
Q: What is RFC 4122 and RFC 9562?
A: RFC 4122 (2005) is the original Internet standard defining UUID format, generation algorithms, and namespace conventions. It specifies versions 1, 2, 3, 4, and 5. RFC 9562 (2024) supersedes RFC 4122 and adds versions 6, 7, and 8 to support modern use cases like time-ordered identifiers and custom application-defined formats.
Q: What does a zero/empty GUID look like?
A: The empty GUID is 00000000-0000-0000-0000-000000000000 — 32 zeros in 8-4-4-4-12 format. It is sometimes called Guid.Empty (in .NET) or the nil UUID. It is reserved as a sentinel value and should never be generated as a real identifier; treat it as "no GUID" or "not set".