The downloaded ZIP is already arranged as a complete pet package. Installation is mostly about keeping that folder intact and placing it in the exact custom pets location that Codex opens for you.
Unzip before moving anything
Double-click the downloaded ZIP and work with the extracted folder. Do not drag individual files out one by one, because the manifest expects the spritesheet and supporting files to stay together.
Use Codex to open the correct folder
Open Codex Settings, choose Pets, scroll to the custom pets area, and use Open folder. This avoids guessing where the hidden .codex directory lives on your Mac.
Keep the generated files at the top level
Inside your pet folder, pet.json and spritesheet.webp should sit directly at the top level. An extra folder nested between them and the pets directory is the most common installation mistake.
- Do not rename pet.json
- Do not rename spritesheet.webp
- Move the whole extracted pet folder
Refresh and select the new pet
Return to Codex after copying the folder, refresh the custom pets list, and choose the new entry. If it does not appear, reopen the folder and check for an accidental double-nested directory.
Unzip the kit, move the whole extracted folder into the directory opened by Codex, keep pet.json and spritesheet.webp at the top level, then refresh Pets.