Invasión Pixel

Ask for it like this

Copy this prompt, paste it into Claude or ChatGPT, and that's it. It's the short version: the minimum for the game to come out playable.

Make me a shoot-the-invaders game for the browser, in the style of the 70s arcades, with original art.

- My ship moves sideways along the bottom and shoots upward, with only one of my shots on screen at a time.
- 5 rows of 11 invaders of three types worth 10, 20 and 30 points. The group moves side to side and steps down when it touches an edge; the fewer are left, the faster they go.
- Invaders shoot at random. Four shields protect me and wear away piece by piece.
- Every so often a mystery ship crosses the top and gives extra points.
- 3 lives; I lose everything if the invaders reach my level. Clearing a wave starts another one, lower down.
- Controls: arrow keys and space on desktop; big on-screen buttons on mobile, usable with both thumbs at once.
Technical: a single HTML file with the CSS and JavaScript inside, no libraries and no external images, everything drawn on canvas. It should fill the window and be playable with a finger on a phone and with keyboard or mouse on a computer.

Getting it as an HTML file

A game like this is a single file you open with a double click. These four steps are the same in any AI.

1. 1. Ask for the whole file

   Add this line at the end of your prompt: Give me a single, complete HTML file, nothing cut out, ready to save as index.html and open in the browser. Without it, you often get the code in pieces.

2. 2. Copy all of the code

   In Claude the game shows up on the side, already running, with a button to copy or download it. In ChatGPT, copy the whole code block: it has to start with <!DOCTYPE html> and end with </html>.

3. 3. Save it as index.html

   Paste it into Notepad (Windows) or TextEdit in plain text mode (Mac) and save it as index.html. Watch out for .txt: if the file ends up as index.html.txt, it won't open as a page.

4. 4. Double-click to open it

   It opens in your browser and it's ready to play, with nothing to install and no internet needed. To share it, upload it to any web host or send it by email: it's just one file.

If the game shows up blank, go back to the AI and paste the error from the browser console (right click → Inspect → Console). With that text it fixes it fast.

The full prompt, the one actually used

Longer and more specific: numbers, screens and style details. It's the one that produced exactly this game, unedited. Use it if you want to fine-tune the result.

Diego wrote it in Spanish and it stays in Spanish on purpose: it's the honest record of how the game was made, and a translation would be a prompt nobody used. Claude and ChatGPT understand it as is; add "Answer in English" if you want the game's text in English.

Hazme un juego de navegador llamado "Invasión Pixel".

La idea: el clásico de disparar a filas de invasores que bajan, al estilo de los arcades de los 70, pero con arte original.

Mecánica:
- Tu nave se mueve a los lados en la parte de abajo y dispara hacia arriba. Solo puede haber un disparo tuyo en pantalla a la vez.
- Los invasores vienen en 5 filas de 11, de tres tipos que valen 10, 20 y 30 puntos. El grupo se mueve de lado a lado y baja un escalón cada vez que toca un borde.
- Mientras menos invasores quedan, más rápido se mueven.
- Los invasores disparan hacia abajo al azar.
- Cuatro escudos protegen tu nave y se van desgastando, a pedazos, con cada disparo, tuyo o de ellos.
- Cada cierto tiempo cruza arriba una nave misteriosa que da puntos extra.
- 3 vidas. Pierdes una si te dan. Pierdes todo si los invasores llegan hasta tu altura.
- Al limpiar una oleada empieza otra, que arranca un poco más abajo.

Pantallas: título con Jugar y la tabla de puntos; el juego con HUD (puntaje, récord, vidas, oleada); y fin con reintentar.

Controles: en PC, flechas o A/D para moverte y Espacio para disparar. En celular, botones grandes en pantalla: izquierda y derecha abajo a un lado, y disparar al otro lado, usables con los dos pulgares.

Estilo: pixel art en blanco, verde y magenta sobre fondo negro con estrellas, invasores animados a dos cuadros, explosiones de píxeles y un leve efecto de pantalla de tubo.

Técnico:
- Un solo archivo HTML con todo el CSS y el JavaScript dentro. Sin librerías, sin CDN, sin imágenes externas: todo dibujado en canvas.
- Tiene que llenar la ventana y adaptarse a cualquier tamaño, de celular a pantalla grande, sin deformarse.
- Tiene que jugarse completo desde celular (solo con el dedo) y desde PC (teclado o mouse).
- Tiene que funcionar dentro de un iframe con sandbox="allow-scripts". El récord va en localStorage dentro de try/catch para que el juego no se rompa si no hay acceso.
- Se pausa solo cuando la pestaña no está visible.
- El texto del juego va en español.

For ChatGPT, add the line from step 1 at the end: it tends to hand over the code in pieces.

What this prompt was missing

What became clear once the game was finished. If you're making your own from this one, add these from the start: fixing things later costs another round.

• Ask for a pause button on mobile too: it was requested for desktop and the phone ended up with no way to pause.
• Set a minimum size for the score text; on a phone held sideways it came out around 9 px.
• Say whether holding the button should fire continuously or one shot at a time.

What was asked after the first result, in Diego's own words (Spanish):

• Agrégale un menú de pausa, un botón para cambiar entre español e inglés, y que el récord no se pierda al recargar.

It works in any AI

Claude, ChatGPT, Gemini, Copilot: the prompt is the same and so is the method. What changes is where you see the result. Four things that hold in all of them:

1. Ask for a single file

   "A single HTML file with everything inside, no libraries or CDN." That way the game works with a double click, with nothing to install, and you can upload it to any website.

2. Ask it to tell you what it assumed

   End with: "before writing the code, tell me in 5 lines what you assumed". That's where the gaps in your prompt show up, while fixing them is still cheap.

3. One fix per message

   Say what happens and what you expected. If you ask for three changes at once, one usually undoes another.

4. Ask it to test, not to promise

   "Check that every level can be won and tell me how you checked." That's how the games on this page found their bugs before going live.

The 6 parts of a good prompt, with a template to copy