Use these reviewed values to observe exact field boundaries. The examples explain what a local structural check can establish and, equally importantly, what it cannot establish about a record or caller.
Text-shape failures
A missing hexadecimal digit changes the length; a moved hyphen changes group boundaries; g is not hexadecimal. Uppercase, braces, urn:uuid and surrounding whitespace may be meaningful representations elsewhere, but UUIDLens does not silently convert them. Submit exactly 36 lowercase characters in the five canonical groups so producer and consumer agree on one testable contract.
Field failures after parsing
A structurally shaped ordinary UUID still fails when the variant bits are not RFC 9562 or when the version nibble is zero or above eight. These errors are different from malformed text because all 16 bytes were parsed successfully. Nil and Max are explicit exceptions: their all-zero and all-one bit patterns are classified before ordinary field rules.
Handle rejection without stale output
When a new value fails validation, discard any previously displayed success before reporting the error. Keep the original input visible so the user can compare it with the contract, but do not upload it or place it in analytics. In an API, return a stable error code and validate authorization separately; never treat a corrected-looking UUID as proof that the referenced resource exists.