Gampangin
Menu
Enter
Client-side

Reference

UUID Format, Versions, and Variants

The 8-4-4-4-12 textual layout, the version and variant fields, and the RFC that defines them.

By Gampangin· Published · Updated · Reviewed by Gampangin· 1 min read· Identifiers and UUIDs

AI-assisted draft. Editorial responsibility: Gampangin.

The canonical UUID text is 32 hexadecimal digits in five groups: 8-4-4-4-12, for example 0197f0a4-1c2d-7b3e-9f10-4a2b6c8d0e1f. The hyphens are formatting only; the value is the 16 bytes.

01Fields

  • The 13th hexadecimal digit is the version, such as 4 or 7.
  • The 17th hexadecimal digit encodes the variant; the RFC 9562 variant has its top bits set to 10.
  • Bits not used by the version and variant fields are free for data.

02Limitations

The format describes how the bits are laid out, not whether the identifier is unique or trustworthy; that depends on how it was generated.

Sources

  1. RFC 9562: Universally Unique IDentifiers (UUIDs) — IETF (accessed 2026-09-27)
  • ToolAPI Key Generator

    Generate prefixed, high-entropy API keys with your browser's cryptographic random source.

  • ToolBase32 Encoder / Decoder

    Encode UTF-8 text to RFC 4648 Base32 or decode a Base32 value back to text.

  • ToolBash Formatter

    Indent and format Bash shell scripts with consistent layout.

  • ToolBasic Auth Generator

    Build an RFC 7617 Basic Authorization header value from a username and password without the credential leaving the browser.

  • ReferenceCSV Format Reference

    A concise reference for RFC 4180 CSV: delimiters, quoting, escaping, line endings and encodings.

  • ReferenceImage and SVG Format Reference

    A concise reference for the PNG, JPEG, WebP and AVIF containers and for SVG, including what each is good at.

  • ReferencePDF Format Reference

    A concise reference for PDF versions, the page tree, metadata and Base64 conversion.

  • ReferenceSQL Syntax Reference

    A concise reference for SQL lexical structure: strings, identifiers, comments and dialect differences.

  • CategoryIdentifiers and UUIDs

    Generate and reason about identifiers, including UUID versions and variants.