What was the early working name for the Pokémon project?

The early working name for the Pokémon project was Capsule Monsters.

Satoshi Tajiri conceived the project around the idea of creatures being stored in capsules and exchanged between players. The concept developed during the long production of the Game Boy games, eventually becoming the Pocket Monsters franchise known in Japan.

The title was reportedly difficult to trademark because similar names already existed, so the project went through naming changes before the Japanese name Pocket Monsters was established. The international name Pokémon is a contraction of “Pocket Monsters.”

The working-title history is easy to confuse with the franchise's final Japanese name. Capsule Monsters was an early development name, not the title of a released main-series Pokémon game or television season. The original concept also changed substantially during development as Game Freak and Nintendo refined the world, battle system, creatures, and trading features.