Build your defense, block by block.

Stackkeep is a compact castle-building defense game. Stack walls, pillars, and beams, then fit weapons, workshops, barracks, and defending troops into a small building area.

Every placement matters. Upper floors need support, buildings can block your ballistas, and troops need room to intercept enemies. Protect your keep through five increasingly varied sieges.

• Build freely, or start with an editable sample castle. 
• Watch your defenses fight automatically, with pause and 2× speed.
• Choose one of three randomized rewards between victories.
• Discover new weapons, specialized upgrades, and unusual building parts.
• Your castle and troops are fully restored between battles, so you can revise your layout for the next siege.

Controls: Tap or click a part, then an empty cell to place it. Select a placed part to move it. Choose Defend when your castle is ready.

For your first game, choose “Start with a sample castle.”

Designed for portrait mobile browsers. Mouse controls are also supported. English and Japanese are available from the language button. BGM and sound-effect volumes can be adjusted separately.

Credits: Human creator: Johnnysuzuki1234 — original concept, design direction, playtesting, and final decisions.

AI tools used

• Code and development: OpenAI ChatGPT / Codex assisted with implementation, design iteration, debugging, code-based testing, and Japanese–English translation.
• In-game art: Canvas/SVG visuals created through AI-assisted code.
• Cover image: Generated with ChatGPT image generation, using actual gameplay visuals as reference.
• Audio: Music and sound effects created through AI-assisted Web Audio synthesis.
• 3D: No 3D assets were used.

Created for Slapjam AI 2026.