Build a playable browser game prototype in one evening with an AI agent

What you end up with

By the end of the evening you have a game in a browser tab that someone else can play, plus three notes on what to change next.

What you get

• One .md playbook with an evening timeline and two worked spec examples
• A one-paragraph game spec template: core loop, controls, win and lose
• Six stage prompts from first build to polish
• Playtest note card for the five-minute test
• Checklist for licensing of generated art, sound and fonts
• Guide to uploading an HTML5 zip to itch.io

Who it is for

Players who have always wanted to make a game, game jam entrants and developers who want to test a mechanic before committing to an engine.

Works with

Solid chips: the agent is named in this listing's own tools list. Dashed chip: Plain Markdown, so it also pastes into other agents such as Grok Bot, Hermes, OpenClaw or Muse. We list those as compatible by format only, not as tested.

Tools needed

Cost to run: Free with most AI coding tools' included usage.
Time to result: 2 to 3 hours to a playable prototype

How it works

1. Write the spec

   Fill in the template: what the player does every few seconds, the controls, how you win, how you lose. One paragraph, no more.

   Expected: A spec short enough to read in 20 seconds.

2. First build in one file

   Ask the agent for a single index.html with a canvas, inline JavaScript and no libraries. Open it in your browser.

   Expected: Something moves on screen and responds to input.

3. Five-minute playtest

   Play for five minutes. Write three notes: one thing that feels good, one that is confusing, one that is missing.

   Expected: Three short notes, not a feature list.

4. Change one mechanic at a time

   Feed the agent one note per prompt. Save a copy of the file each time it still works.

   Expected: A folder of working versions you can go back to.

5. Add feedback and feel

   Ask for sound effects generated in code, a small screen shake on hits and a score display.

   Expected: The game feels responsive even with placeholder art.

6. Share it

   Zip index.html, upload it to itch.io as an HTML game and set it to be played in the browser.

   Expected: A link you can send to friends tonight.

Sample prompt from the pack

Build a browser game from this spec: [paste your one-paragraph spec].
Constraints: one file named index.html, a single canvas, inline JavaScript, no external libraries or assets. Shapes and colors only for art.
Include: a start screen, a game over screen with restart, keyboard controls and touch controls for phones.
Keep the game logic in clearly named functions (update, draw, reset) so I can ask for changes later.
When done, tell me in three lines how to play it and what you left out.

Free preview of the file

# Build a playable browser game prototype in one evening with an AI agent

PaperChase agent use case pack (playbook), version 1.0. For Claude Code, Cursor, Codex or any chat model that writes code. Time: 2 to 3 hours.

## The plan for tonight

| Time | Stage | You end with |
|---|---|---|
| 0:00 | Write the spec | One paragraph you could read aloud in 20 seconds |
| 0:15 | First build | A single index.html where something moves and responds |
| 0:45 | Five-minute playtest | Three notes: good, confusing, missing |
| 0:55 | Change one mechanic at a time | A folder of working versions |
| 1:45 | Feedback and feel | Sound, hit feedback, a score |
| 2:15 | Share it | An itch.io link you can send tonight |

## Rules that keep the evening on track

1. One file. No libraries, no build tools, no images. Shapes and colors only.
2. Save a copy every time it works: `v1.html`, `v2.html`, and so on.
3. One change per prompt. Never "and also".
4. Stop adding features at 1:45 even if you have ideas. Write them down for tomorrow.

## Contents

1. Spec template, with two filled-in examples
2. Stage prompts 1 to 6
3. Playtest note card
4. When the agent breaks it
5. Licensing checklist for art, sound and fonts
6. Posting on itch.io

Worth knowing

• Agents often break controls when adding features. Save a working copy before every change.
• Do not clone a trademarked game or use its name. Make the idea yours.
• If you add generated art or music later, check the license terms of the tool that made it before you sell anything.

Details

Version 1.0 · Updated Oct 15, 2026 · Markdown version of this page
License: Personal and commercial use. The games you make are yours. Download terms

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