UUID Decoder & Inspector UUID Analysis Tool

UUID (Universally Unique Identifier) is a 128-bit identification standard used to uniquely identify information in distributed systems. The standard format is 32 hexadecimal characters divided into five hyphenated groups:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx。

The core value of UUID is that it can generate a globally unique identification code without the need for a central registration authority, which is extremely important in scenarios such as database primary keys, distributed tracking, and work stage identification.

RFC 4122 (2005) is the original UUID standard, defining four versions: v1, v3, v4, and v5. RFC 9562 (May 2024) is an updated version, adding v6, v7, v8 and retaining backward compatibility.

Major changes include:
• v6 is compatible with v1 but fields are reordered to make them sortable in the database
• v7 uses Unix millisecond timestamps, replacing v1's 1582 year base, which is simpler and more in line with modern needs
• v8 is an experimental custom format that allows developers to define their own column layouts
• It is recommended that new applications use UUID v7 for best performance and sortability

The main reasons why UUID v7 is recommended:

• Sortable: The high bit is the timestamp, so sorting by UUID in the database means sorting by creation time, which greatly improves B-Tree index performance
• High efficiency: No need for global locking or node ID, fast generation
• Privacy: Unlike v1 which exposes MAC address and precise time
• random enough: 74 bits random part provides approximately 2.4 × 10²² combinations
• Standardization: Incorporated into RFC 9562, supported by mainstream databases such as MySQL 8.0+, PostgreSQL, and SQLite

For new systems, UUID v7 is generally a better choice than v4 unless there are specific compatibility requirements.

Variant represents the byte layout specification of the UUID, determined by the high-order bit of the 9th byte:

• NCS (0xxx): Early NCS format, now rarely used
• RFC 4122 (10xx):Current standard format (most common)
• Microsoft (110x): Microsoft GUID compatible format
• Reserved (111x): reserved for future definition

Most modern UUIDs use RFC 4122 Variants, and you can use this tool to quickly confirm the Variant used by a UUID.

There are almost no technical differences. GUID (Globally Unique Identifier) ​​is Microsoft's implementation of the UUID standard and is used in technologies such as Windows COM/OLE. Both follow the RFC 4122 specification and have the same format (128 bits, 32 hexadecimal characters).

The only minor difference is that Microsoft GUIDs are sometimes output in mixed endian format (different order of bytes within hyphen groupings), but this only affects display, not uniqueness. You can safely treat UUIDs and GUIDs as the same thing.

A Nil UUID (also called a Zero UUID) is a special UUID in which all bytes are 0:00000000-0000-0000-0000-000000000000. It does not represent any actual identifier, and is often used to indicate a "no value" or "unset" state, similar to NULL in a database or the nil/null concept in programming languages.