DuplicateItemsInUniqueArraysFields

Item	Description
Full Fuzzer Name	DuplicateItemsInUniqueArraysFieldsFuzzer
Log Key	N/A; the fuzzer name and mutation scenario identify the test.
Description	Inserts a duplicate item into arrays declared with uniqueItems: true.
Enabled by default?	Yes.
Target field types	OpenAPI arrays with uniqueItems: true and a mutable non-empty value.
Expected result	4XX, because the duplicate violates the contract.
Fuzzing logic	Replaces each eligible array with a copy containing a duplicate item and sends the mutated request.
Conditions when this fuzzer will be skipped	When the payload is invalid JSON, no eligible unique array is present, the array is empty, or the target is reference data.
HTTP methods that will be skipped	HEAD, GET, DELETE.
Reporting	Reports a rejected duplicate as the expected result; unexpected response codes and server errors are reported as errors.

This fuzzer targets arrays declared with uniqueItems: true. It replaces the array with a value containing a duplicate item and checks whether the service rejects the invalid request instead of silently accepting duplicate values.

Select it with:

cats -c openapi.yml -s http://localhost:8080 \
  --fuzzers=DuplicateItemsInUniqueArraysFields