What is a Vertical/Horizontal Slice?

Vertical Slice and Horizontal Slice are two foundational concepts in game development used to evaluate progress, test risk, and communicate across disciplines.

They serve different purposes:

Vertical Slice = proof of vision and polish
Horizontal Slice = proof of systems and structure

You’ll likely need both.

1️⃣ Definition

Term	Definition
Vertical Slice	A small but highly polished segment of the game that represents the final quality and experience
Horizontal Slice	A broad, unpolished implementation of all core systems, used to test structure and dependencies

📍One slice asks: “Does it feel right?”. The other: “Does it hold together?”

2️⃣ Why Slices Matter

Purpose	Vertical Slice	Horizontal Slice
Test core experience	✅	✅
Validate design vision	✅	❌
System integration	⚠️ Partial	✅
Pitch to publisher/stakeholder	✅	❌
Discover tech risks early	⚠️ Less ideal	✅
Establish final quality bar	✅	❌
Enable early iteration	❌	✅

📍Vertical = what the player will feel. Horizontal = what the team will build

3️⃣ What Each Slice Contains

Vertical Slice

Component	Status
Core gameplay loop	Polished and tuned
Art & animation	Final or near-final
UI / UX	Functional and styled
Audio	Synced and layered
Environment / level	Fully playable and narrative-aware
QA	Testable as if shipping

📍Use it to lock the feel and direction.

Horizontal Slice

Component	Status
All core systems	Present but rough
UI / UX	Wireframe or debug-ready
Assets	Placeholders and graybox
Progression systems	Stubs or base logic
AI, combat, economy	Integrated but unbalanced
Tooling / save / debug	Ready for testing and iteration

📍Use it to test what connects to what — and what breaks.

4️⃣ Analogies

Metaphor	Meaning
Vertical slice	One slice of cake: fully baked, layered, frosted
Horizontal slice	All cake layers laid out: no icing, just structure

📍If your game was a building:

Horizontal = scaffolding
Vertical = decorated sample apartment

5️⃣ When to Use Each

Goal	Use...
Show off polish	↕️ Vertical Slice
Test if design is fun	↕️ Vertical Slice
Stress-test integration	↔️ Horizontal Slice
Prepare tools + pipeline	↔️ Horizontal Slice
Attract funding	↕️ Vertical Slice
Find bugs early	↔️ Horizontal Slice

📍Don’t choose one. Use both — but in the right order.

✅ Slice Design Checklist

Question	Vertical	Horizontal
Does it represent the player’s final experience?	✅	❌
Can we iterate on all core systems?	❌	✅
Is this testable with users or stakeholders?	✅	⚠️ Internal only
Can it break safely?	❌	✅
Will it help decide quality bar?	✅	❌

Summary

Term	Vertical Slice	Horizontal Slice
What it is	Final-quality mini-demo	Working system skeleton
Why it matters	Proves vision, guides polish	Tests architecture, supports iteration
Who uses it	Publishers, creative leads	Engineers, QA, internal team
Design goal	Lock the feel	Validate the structure

📍One proves what it will be. The other ensures how it will be built.