FOR OPENPETS

The output, precisely

Atlas

1536 x 1872, PNG or lossless verified WebP

Grid

8 columns x 9 rows, 192 x 208 per cell

Rows

idle 6, run right 8, run left 8, waving 4, jumping 5, failed 8, waiting 6, working 6, review 6

Alpha

unused cells fully transparent, zero RGB behind every transparent pixel

Manifest

pet.json with id, displayName, description, spritesheetPath

That last alpha rule is the one hand built packs fail most often. Plenty of editors leave colour data sitting behind a zero alpha channel, and a strict validator rejects the sheet without telling you why. Hatchery checks it in the browser before the download button turns on, then re-checks the encoded file after export, falling back from WebP to PNG if the encode is not clean.

Three steps

1. Build or download. Use the builder for something new, or take a pack from the gallery if you only want to test your renderer.
2. Check the sheet. Every pack page previews all nine rows at their real frame durations, so you can compare against your own timing table before installing anything.
3. Drop the folder in. Unzip into the pets directory OpenPets watches. The folder name is the id and it already matches pet.json.

unzip -o my-pet.zip -d ~/.codex/pets/

Row semantics we hold to

The frame counts are only half the contract. The other half is what each row means, and getting that wrong is what makes a pet feel off even when it validates. running is the working state, focus and effort, not locomotion, so nothing in that row jogs or travels. running-left is derived from running-right by mirroring each frame in place, which preserves order and timing. idle stays calm enough to double as the reduced motion frame.