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UUID Validator

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Validate any UUID (v1–v5) instantly — checks the 8-4-4-4-12 hexadecimal format and identifies the version. Free, client-side, no sign-up required.

What is a UUID?

A UUID Validator checks whether a string is a correctly formatted UUID (Universally Unique Identifier) according to the RFC 4122 standard. A UUID is a 128-bit identifier expressed as 32 hexadecimal digits arranged in the pattern 8-4-4-4-12 — for example, 550e8400-e29b-41d4-a716-446655440000. UUIDs appear throughout software development as database primary keys, API request identifiers, session tokens, file names, and anywhere a unique identifier needs to be generated without central coordination.

The RFC 4122 standard defines five UUID versions. Version 1 is time-based and encodes the current timestamp and MAC address. Version 2 is used in DCE security systems. Versions 3 and 5 generate deterministic UUIDs from a namespace and name using MD5 or SHA-1 hashing respectively. Version 4 — by far the most common — uses random or pseudo-random bits, making collisions statistically negligible. Each version encodes its number at a specific position in the UUID string (the 13th hex digit), which is how this validator detects and reports the version.

Beyond format, the RFC 4122 standard also specifies a variant byte at position 19 in the UUID string. RFC 4122-compliant UUIDs use a variant byte of 8, 9, a, or b. Older NCS compatibility UUIDs and Microsoft COM/GUID UUIDs use different variant bytes. This validator checks all three layers: correct hexadecimal characters, correct 8-4-4-4-12 structure, valid version (1–5), and RFC 4122 variant byte.

If you are working with API responses and want to verify that IDs are well-formed, you can also use the URL Validator and Email Validator to check other common identifier formats.

How to use this UUID calculator

  1. Copy the UUID string you want to check — from a database record, API response, log file, or form input.
  2. Paste it into the UUID input field on this page.
  3. The validator runs instantly — no button press needed.
  4. Check the Valid / Invalid badge below the input.
  5. If valid, read the details breakdown: format confirmation, version name, and variant.
  6. If invalid, read the error message — it specifies the exact problem (wrong length, bad characters, unrecognised version, or invalid variant byte).
  7. Fix the UUID in your source and re-paste to re-validate.

Formula & Methodology

A UUID is validated against this regular expression (case-insensitive):

/^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i

Breaking this down:
- [0-9a-f]{8} — 8 hexadecimal characters (first group)
- -[0-9a-f]{4} — hyphen + 4 hex chars (second group)
- -[1-5][0-9a-f]{3} — hyphen + version digit (1–5) + 3 hex chars (third group)
- -[89ab][0-9a-f]{3} — hyphen + RFC 4122 variant byte (8/9/a/b) + 3 hex chars (fourth group)
- -[0-9a-f]{12} — hyphen + 12 hex chars (fifth group)

Valid example: 550e8400-e29b-41d4-a716-446655440000 — UUID v1, 36 characters, RFC 4122 variant.

Invalid example: 550e8400-e29b-61d4-a716-446655440000 — fails because position 14 is 6, which is not a valid UUID version (valid range: 1–5).

Version is read from character at index 14 (0-based) of the UUID string. Version labels: v1 = time-based, v2 = DCE security, v3 = namespace/MD5, v4 = random, v5 = namespace/SHA-1.
Frequently Asked Questions
What is a UUID?
A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier), is a 128-bit identifier formatted as 32 hexadecimal digits separated into five groups: 8-4-4-4-12. For example: 550e8400-e29b-41d4-a716-446655440000. UUIDs are designed to be unique across time and space without requiring a central registry.
What UUID versions does this validator support?
This validator supports all five RFC 4122 UUID versions: v1 (time-based), v2 (DCE security), v3 (namespace with MD5 hashing), v4 (randomly generated), and v5 (namespace with SHA-1 hashing). The version number is encoded at position 13 of the UUID string (the first character of the third group).
What does the UUID format 8-4-4-4-12 mean?
The numbers refer to the count of hexadecimal characters in each hyphen-separated group. A complete UUID is always 36 characters long: 8 hex chars, a hyphen, 4 hex chars, a hyphen, 4 hex chars, a hyphen, 4 hex chars, a hyphen, and 12 hex chars. The total hex digit count is 32 (128 bits).
What is the difference between UUID and GUID?
UUID and GUID refer to the same concept. UUID is the term used in the RFC 4122 standard, while GUID (Globally Unique Identifier) is the term used by Microsoft in its COM/OLE systems. Structurally they are identical — both are 128-bit identifiers in the 8-4-4-4-12 hexadecimal format. This validator accepts both uppercase and lowercase hex digits.
How do I validate a UUID?
Paste your UUID string into the input field. The validator checks it live — no button press needed. You will see a Valid or Invalid badge, and if valid, the UUID version is identified. If invalid, a specific reason is shown (wrong length, invalid characters, unrecognised version, or wrong variant byte).
What should I do if my UUID is invalid?
Check the error message shown below the badge — it specifies exactly what is wrong. Common issues are: missing or extra hyphens, non-hexadecimal characters (like g, h, or spaces), a version digit outside 1–5, or a variant byte that is not 8, 9, a, or b. Copy the UUID directly from its source rather than retyping it to avoid transcription errors.
Does this validator confirm that a UUID is unique or registered?
No. This tool performs a structural format check only — it confirms that the UUID follows the correct 8-4-4-4-12 hexadecimal format and is a valid RFC 4122 identifier. It does not and cannot verify that the UUID is unique, that it was generated correctly, or that it exists in any system. UUID uniqueness is a statistical property of the generation process, not something that can be verified by inspecting the string.
Is my UUID sent anywhere when I validate it?
No. All validation happens entirely in your browser — nothing is transmitted to any server, stored, or logged. UUIDs often appear in database primary keys, API tokens, and session identifiers, so client-side processing is important for privacy.
What is the UUID variant byte and why does it matter?
The variant byte is the first character of the fourth group (position 19 in the UUID string). RFC 4122 UUIDs — the most common type — use a variant byte of 8, 9, a, or b. This is part of the UUID specification and distinguishes RFC 4122 UUIDs from older NCS or Microsoft COM UUIDs. If the variant byte is anything else, the UUID does not conform to RFC 4122.
Can I use uppercase hex characters in a UUID?
Yes. The validator accepts both uppercase (A–F) and lowercase (a–f) hexadecimal characters. The RFC 4122 standard recommends lowercase for canonical representation, but uppercase is equally valid and widely used, particularly in Windows/GUID contexts.
What is UUID v4 and why is it so common?
UUID v4 is randomly generated — 122 of its 128 bits are cryptographically random, making collisions astronomically unlikely. It is by far the most common UUID version in modern software because it requires no coordination, no timestamp, and no namespace seed. Most UUID generation libraries (including crypto.randomUUID() in browsers) produce v4 UUIDs by default.
What is the difference between UUID v3 and v5?
Both v3 and v5 are namespace-based UUIDs — they generate a deterministic UUID from a namespace UUID plus a name string. The difference is the hashing algorithm: v3 uses MD5 and v5 uses SHA-1. The same namespace and name always produce the same UUID, which makes them useful for content-addressable identifiers. V5 is preferred over v3 because SHA-1 is more collision-resistant than MD5.

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