debuff vs KAPLAY

KAPLAY and debuff are both small JavaScript toolkits for 2D browser games, and both aim to get you to a playable game quickly. KAPLAY continues the Kaboom.js line, with a friendly component API and an online playground. debuff puts its weight on deterministic testing and working with coding agents. Here's how they compare as of October 2026.

Short answer

Pick KAPLAY if you want the gentlest start: a playful API, a browser playground with lots of examples, and an established community. Pick debuff if you want deterministic tests, fuzzing and an agent that can attach to your running game.

At a glance

	debuff 0.2	KAPLAY 3001.0.19
License	MIT	MIT
Language	TypeScript	JavaScript, with TypeScript support
API style	Scenes with update and render, immediate-mode drawing	Game objects built from components (pos, area, body)
Physics	Tile collision	Simple body physics and collisions built in (README)
Try it in the browser	Examples on debuff.jp	KAPLAYGROUND with 90+ examples
Full runtime, brotli	20 kB (every debuff package)	59 kB (kaplay.mjs)
Testing	Scenarios, screenshot baselines, fuzz	Up to you
Coding agents	MCP server for the running game, AGENTS.md	No llms.txt (404), no official MCP found
Community	Small	Established (Discord, subreddit, itch.io jams)

Full runtime download, brotli (kB, smaller is better)

debuff20 kB

KAPLAY59 kB

Each library's complete prebuilt bundle (all debuff packages, kaplay.mjs), compressed with brotli and measured on 17 October 2026. Tree-shaken games ship less.

KAPLAY's stable line is 3001; a v4000 preview is available on npm under the next tag.

Where KAPLAY is stronger

• First hour. The component API reads almost like a description of the game, and KAPLAYGROUND lets you try things without installing anything.
• Built-in gameplay helpers. Bodies, collisions, state machines and effects like screen shake are a function call away.
• Community. It inherits Kaboom's audience and has an active Discord and regular jams.

Where debuff is different

• Determinism. debuff runs on a fixed-step clock with a seeded RNG, so the same input gives the same game. That's what makes its scenarios, exact replays and fuzzing possible.
• Testing built in. npm test runs scenario scripts headless with screenshot baselines. npx debuff fuzz plays with random input and saves each crash or stuck state as a scenario that reproduces it.
• Agent tooling. KAPLAY's AI guide is about game AI (state machines and rule systems), not coding agents. debuff ships an MCP server, an AGENTS.md in every new project, and workflows such as tune-feel and fix-errors. See the agent comparison post.
• Typed params. Feel values have types, ranges and units, show up as sliders in the dev overlay, and can be tuned by an agent within those ranges.

Which to choose

For learning, jams with friends, or the quickest path to something on screen, KAPLAY is a great choice. If you want tests and an agent in the loop from the start, try debuff:

npm create debuff@latest my-game