The de jure flag of Košice. This is made official by the Heraldic Registry of the Slovak Republic, which shows an image of the flag (its colors likely based off the coat of arms.)For an unknown reason, the city of Košice's government, instead, favors a flag of yellow and blue, without the swallowtail (usually with the coat of arms), which falls outside the regular pattern of Slovakian municipal flags. This flag, with its swallowtail, is rarely seen throughout.
https://ives.minv.sk/heraldreg/wp_detail.aspx?ID=3250
Author unknown, Jozef Králik, Ladislav Čisárik