Game Creation With Codex And Claude Code — Aula 1: From Game Idea to Realistic Scope

What if your first browser game could begin with a clear brief and two strong agent plans? That is the goal of this lesson: not to build the biggest possible game, but to define a small, playable browser project that Codex and Claude Code can understand, plan, review, and help you finish.

If 50 tools can exist just for one media category, imagine how quickly a game project can expand when you add physics, animation, enemies, inventory, saving, mobile controls, music, and online play. Your first job is to reduce the idea before asking an agent to build it.

From Idea to Buildable Brief

A game idea becomes buildable when it can answer four questions:

1. What does the player do every few seconds?
2. What counts as success?
3. What screens are required?
4. What should not be included in version one?

For a first browser game, your target is a playable loop, not a complete commercial product. Good first projects are small enough to explain on one page and test in a browser in minutes.

Why First Game Projects Break

A dangerous first project often sounds exciting:

• Open world exploration
• Real-time combat
• Inventory and crafting
• Multiplayer
• Procedural maps
• 3D enemies
• Save files
• Mobile controls
• Dialogue trees

Each feature may be reasonable by itself. Together, they create a planning problem before you have a game.

A stronger first game starts with one mechanic and a clear finish line:

• Match cards before time runs out
• Jump over obstacles
• Click to earn points and buy one upgrade
• Answer 10 questions and receive a score
• Drag objects into correct zones
• Avoid falling shapes for 60 seconds

The lesson for game creators is direct: if behavior is not defined, even simple features expand. A “basic inventory” can become item categories, stacking rules, drag behavior, keyboard shortcuts, persistence, error states, and UI design. Define the feature before asking for code.

Good First Game vs. Dangerous First Game

Case Study: Sprite Garden

Sprite Garden is a small HTML Canvas 2D sandbox and farming project. It is a useful reference for a first browser game because it demonstrates the right kind of ambition: visible interactions, a simple world, and browser sharing.

You do not need to clone its features. You need to copy its discipline. It is not trying to become a full farming RPG in the first milestone. It gives the player something understandable to do.

Pick One Core Mechanic

Your core mechanic is the repeated action that creates the game. It should fit in one sentence.

Good examples:

• Match two cards with the same symbol.
• Jump over obstacles and survive for 60 seconds.
• Click objects before they disappear.
• Answer questions before time runs out.
• Drag ingredients into the correct basket.

Weak examples:

• Explore a fantasy world and become powerful.
• Build a complete RPG with combat and crafting.
• Make a multiplayer survival game.
• Create a 3D platformer with enemies and bosses.

My game is a browser game where the player [single verb] to [clear goal]. The first playable version is successful when [measurable outcome]. Exclude [features not in v1].

My game is a browser game where the player answers trivia questions to score 10 points before the timer ends.
The first playable version is successful when it runs locally, includes 10 questions, shows feedback after each answer, and displays a final score.
Exclude accounts, leaderboards, multiplayer, animations beyond basic transitions, and custom art generation.

Mini GDD: Eight Constraints Before Code

A mini GDD is a compact game design document. It should not be a 40-page design bible. For this course, use eight fields:

1. Game idea
2. Player goal
3. Core loop
4. Controls
5. Rules
6. Screens
7. Visual and audio style
8. Success criteria

One-Page Game Brief Template

Use this structure before opening an implementation task.

Game idea: [one sentence]\nPlayer goal: [what the player tries to achieve]\nCore loop: [repeatable action sequence]\nControls: [mouse, keyboard, touch, or simple combination]\nRules: [3 to 6 rules]\nScreens: [start, game, results]\nVisual style: [simple, feasible browser visuals]\nAudio: [none, basic effects, or simple background loop]\nSuccess criteria: [measurable done state]\nOut of scope for v1: [features to reject]

Game idea: A browser trivia game about climate facts.
Player goal: Score 10 points before the timer ends.
Core loop: Read question, choose answer, receive feedback, continue.
Controls: Mouse click or keyboard number keys.
Rules:
- One question appears at a time.
- Correct answers add 1 point.
- Wrong answers show the correct explanation.
- The game ends after 10 questions or when the timer reaches zero.
Screens: Start, game, results.
Visual style: Clean cards, high contrast, simple progress bar.
Audio: No audio in v1.
Success criteria: Runs locally, has 10 questions, no broken states, final score appears.
Out of scope for v1: Login, leaderboard, AI-generated questions, multiplayer, custom character art.

Codex Versus Claude Code: Agent Roles

Codex and Claude Code can both help with coding work, but you should assign them clear roles.

The strongest workflow is not “ask one agent to make the whole game.” It is:

1. Write the brief.
2. Ask both agents for plans.
3. Compare risks.
4. Choose the smaller milestone.
5. Implement one playable version.
6. Review behavior against success criteria.

Master Planning Prompt for Both Agents

Before writing code, ask both agents for a plan. The wording matters: tell the agent not to implement yet.

Read this mini GDD. Do not write code yet. Identify assumptions, risks, files to inspect, and a small implementation plan. Keep the first milestone playable in the browser. Return tasks in order, with acceptance criteria for each task. Prefer the smallest architecture that can satisfy the brief.

Read this mini GDD. Do not write code yet.

Identify:
1. Assumptions that need confirmation
2. Scope risks
3. Files to inspect or create
4. A small implementation plan
5. Acceptance criteria for each task

Constraints:
- Keep the first milestone playable in the browser.
- Prefer simple HTML, CSS, and JavaScript unless the repository already uses a framework.
- Do not add multiplayer, accounts, databases, generated art, or complex animation.
- Return the plan first. Wait for approval before implementation.

Validation Tools for Comparing Agent Plans

You need a way to compare outputs, not just generate them. These tools and resources help you evaluate agent plans more rigorously.

These statistics are not about game design directly. They show a larger pattern: AI-assisted projects often depend on tool selection, automation, and validation. For your first game, do not let the tooling layer become larger than the playable loop.

How to Compare Two Agent Plans

When Codex and Claude Code return different plans, do not ask, “Which one sounds more impressive?” Ask, “Which one gets to a playable milestone with less risk?”

Use this review checklist:

• Does the plan preserve one core mechanic?
• Does it avoid unnecessary dependencies?
• Does it define files to inspect or create?
• Does it include acceptance criteria?
• Does it keep media simple?
• Does it identify assumptions?
• Does it produce a browser-playable milestone?

Compare these two agent plans for the same mini GDD. Choose the smaller first milestone. Identify unnecessary complexity, missing assumptions, testing gaps, and the clearest acceptance criteria. Do not merge both plans unless the merged plan is still smaller than either original plan.

Compare Plan A and Plan B for the same first browser game.

Evaluate:
- Smallest playable milestone
- Risk of scope creep
- Dependency complexity
- Testability in the browser
- Clarity of acceptance criteria
- Missing assumptions

Return:
1. Recommended plan
2. What to remove
3. What to implement first
4. What to test before adding features

Write Success Criteria Before Code

Success criteria make the first milestone testable. Without them, the agent may keep adding features because “done” is undefined.

Bad success criteria:

• Make it fun.
• Add nice graphics.
• Make the game polished.
• Create a complete prototype.

Better success criteria:

• The game runs locally in the browser.
• The player can start, play, and finish one round.
• There are 10 questions.
• Correct and incorrect answers show feedback.
• The result screen displays score and restart.
• No console errors appear during normal play.

The Stella example is a reminder that game behavior needs reproduction steps. When you write your own success criteria, you are also writing the future bug report format.

Turn this game brief into testable acceptance criteria. Use checklist format. Include start state, main interaction, feedback, ending condition, restart behavior, and visible error states. Do not add new features.

Turn this game brief into testable acceptance criteria.

Include:
- Start screen behavior
- Main interaction behavior
- Scoring rules
- Feedback after player input
- Ending condition
- Results screen
- Restart behavior
- Basic error states

Do not add new features.
Do not suggest future roadmap items unless they are clearly marked as out of scope.

Plan Before Implementation

The action sequence for this lesson is simple, but important.

Use the approved plan only. Implement the first playable milestone. Do not add features outside the brief. After implementation, summarize changed files, how to run the game, and which acceptance criteria are satisfied.

Use the approved plan only.

Implement the first playable milestone.
Do not add features outside the brief.

After implementation, report:
1. Changed files
2. How to run the game locally
3. Which acceptance criteria are satisfied
4. Any criteria not yet satisfied
5. Suggested next smallest improvement

Practice: Reduce a Game Idea

Take this vague idea:

“I want to make a cozy fantasy game where players collect creatures, explore different areas, upgrade their home, complete quests, and share progress online.”

A realistic first browser version could become:

“Make a browser collection game where the player clicks one of three zones, discovers a creature card, and tries to collect five unique creatures before running out of 10 turns.”

That reduced version has:

• One core action: choose a zone
• One resource: turns
• One collection goal: five unique cards
• Three screens: start, game, results
• Simple visuals: cards and zones
• No accounts, online sharing, inventory, or quests

When the Two Agents Disagree

Sometimes Codex and Claude Code will recommend different architectures. For example, one may suggest a small React app, while another suggests plain JavaScript. One may suggest a state machine, while another suggests simple object state.

Do not decide based on which plan sounds more advanced. Decide based on the first playable milestone.

Resources for This Lesson

Key Takeaways

The strongest first deliverable is not code. It is a small, testable, agent-friendly game brief.

A good first browser game has one core mechanic, a few screens, simple controls, constrained media expectations, and measurable success criteria. Codex and Claude Code become much more useful when you ask them to plan before implementing.

Your next step is to set up the project and agent workflow. In the next lesson, you will move from brief to working environment, then use the USD 10 course workflow to build toward a playable first browser game with disciplined scope.

Materiales de practica y visuales

Estos recursos complementan la leccion escrita y sirven para repasar, practicar o reutilizar la clase.

Entregables

• Podcast NotebookLM brief – Brief con fuentes, tono y estructura sugerida para audio complementario.
• Learning pack JSON – Manifest estructurado para automatizar web, podcast, adjuntos y QA.
• Sources JSON – Fuentes, videos y recursos gratis en formato estructurado.
• Prompts copiables – Prompts listos para copiar y adaptar.
• Checklist accionable – Lista de avance para completar despues de la clase.
• Mini-proyecto – Trabajo practico corto con entregables concretos.
• Rubrica de autoevaluacion – Criterios para evaluar comprension y aplicacion.
• Glosario – Terminos clave de la leccion.
• FAQ – Preguntas frecuentes para el alumno.
• Adjuntos – Indice de logos, screenshots, infografias y otros recursos.

Infografias

!50

!Good First Game vs. Dangerous First Game

!95 comments

!Mini GDD: Eight Constraints Before Code

!Codex Versus Claude Code: Agent Roles

!Validation Tools for Comparing Agent Plans

!43 comments

!Plan Before Implementation

!The strongest first deliverable is a small, testable, agent-friendly game brief.

Logos y referencias visuales

Podcast complementario

• Brief para NotebookLM o produccion interna: learning-pack/podcast-notebooklm-brief.md