KUMODeck

Use cases

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A backend for your vibe-coded game or app

Yes, a vibe-coded game or app can get a backend without you setting one up. KUMODeck gives your AI hosting, a place for keys, cloud saves, sign-in and multiplayer rooms, and your AI turns on only the parts you ask for. You check each part on a test link before anyone else sees it.

A game or app made with an AI in an afternoon is usually one page that runs in one browser. That is fine until other people use it. Then it needs a few things a single page cannot do on its own: an address that stays up, somewhere to keep each user's data, a way to sign in, sometimes other players in the same room, and a place for the keys that must not be in the page.

KUMODeck is a backend for that, made to be set up by the AI you already use. You ask in plain words; your AI turns on only the parts you ask for. This page lists them in the order most projects need them, with what to ask, what happens, and how to check it.

Connect your AI first#

You do this once. Where you use AI decides how:

Start here picks the right steps for you. Anyone can sign up; an invite code is optional and adds credit to your balance.

1. An address that stays up#

Ask: "Put this online with KUMODeck and give me the test version's link."

What happens: your AI sends the folder and you get a test address with --dev in it. When you say "publish it", you press Publish on a KUMODeck page, and it goes to the public address. Every version is kept, and switching back is instant.

Check: open the link on your phone. Static sites and server-rendered apps (Next.js, Astro, SvelteKit and others) both work: Hosting & deploy.

2. Keys out of the page#

A vibe-coded app often calls an AI model or another service straight from the page, with the key in the JavaScript. Anyone who opens the page can copy that key and use it on your bill.

Ask: "Move the API key out of the page. Open the box so I can enter it, and call the service from a function."

What happens: you paste the key into a small KUMODeck page, never into the conversation. Your AI moves the call into Functions, your own server code, and the page calls the function instead.

Check: deploy again. KUMODeck stops any deploy whose files contain a key you saved, a known secret-key shape (OpenAI, Anthropic, Stripe, Supabase, AWS and many more) or text that looks like a key, and says which file and line (Secrets in deployed files).

3. Data that follows each user#

Ask: "Save each user's progress and settings to the cloud with KUMODeck."

What happens: your AI turns on cloud saves and stores a JSON document per user under a slot key. Users start as guests, so this works before anyone signs up.

Check: use the test link, close the tab, open it again; the data is there. For data a user must not be able to change, such as anything shared between users, ask your AI to keep it in your own database through Functions instead (Cloud saves).

4. Sign-in#

Ask: "Add Sign in with KUMODeck so users keep their data on every device."

What happens: users who started as guests sign in with X, Discord, Google or an email link and keep everything. You do not register an app or copy keys with any of them. Your app gets an ID and a display name, never the email.

Check: sign in on the test link, then on a second device. The walkthrough is in Add login and cloud saves to a vibe-coded game; every option is in Authentication.

5. Other people in the same game (games only)#

Ask: "Make it playable online."

What happens: your AI asks one short question, who plays and how fast the game is, and builds rooms with a 6-letter code or quick match. There is no game server to write.

Check: open the test link in two tabs, the second with ?player=2. See Make your Claude Code game multiplayer and Play online together.

6. A link that looks good when you post it#

Ask: "Turn on KUMODeck's sharing tools and add the card tags for X."

What happens: your AI turns on card images, share links and traffic per post, and puts the card tags into your page's <head>. Each tool is off until you turn it on.

Check: paste the published link into a draft post on X and look at the card (Sharing on X).

An example: one of Sara's games#

Sara is one of us at KUMODeck and makes small browser games with an AI to try it out. For a one-on-one game like Crown Clash, a three-minute tower battle, step 5 is the one that matters. A solo game like Flap NYC needs only step 1, and step 3 if it should remember the best score. You do not need every part: each one is optional, and you pay only for the parts you use.

What it cannot do, and conditions#

  • Your AI has to support MCP or run commands. Claude Code, Codex, Cursor and the Claude, ChatGPT and Muse apps work.
  • Saves are per user, not a shared database. Data shared between users, or data a user must not change, goes in your own database through Functions.
  • It runs on Cloudflare, with Cloudflare's limits. For example, 128 MB of memory per request and 64 MiB for a server-rendered app (Limits).
  • Multiplayer rooms are for small rooms. Competitive fast-action games that need the server to run the game, such as shooters, are not a fit.
  • Paid parts pause at a $0 balance. Your data is kept, and everything resumes by itself about 30 seconds after a top-up.

What it costs#

There is no free tier and no plan to pick. What you use is taken from a prepaid balance at cost, from the first request; an invite code adds $5 of credit for usage fees. Because it is prepaid, a bill cannot run away from you: you get a low-balance email first, and if the balance reaches $0, the parts that cost money pause until you top up. Automatic top-up keeps a busy game from pausing. Details and worked examples: Pricing.

What stays yours#

The code, the images and the data you upload belong to you. Your users see your app at your address or your own domain, with no KUMODeck branding in front of it. How the pieces fit together is on Concepts.

Questions and answers#

Do I have to choose all the parts up front?#

No. Each part is off until your AI turns it on, and you pay only for the parts you use. Many games need only hosting at first.

Can I keep my Supabase or Firebase database?#

Yes. You can keep an existing database and use KUMODeck only for the parts you want, such as hosting and rooms. A game hosted somewhere else can also use KUMODeck's sign-in, saves or rooms once its address is listed in web.allowedOrigins (Hosting & deploy).

Which AI tools can set this up?#

AI agents that support MCP, such as Claude Code, Codex and Cursor, and the Claude, ChatGPT and Muse apps in a browser. Agents that run commands can also use the KUMODeck CLI with one pasted line.

Do I need a Cloudflare account?#

No. Your app runs on Cloudflare through KUMODeck, so there is no Cloudflare account of your own to make. The limits that come from Cloudflare are the same as on your own account and are listed on Limits.

My AI put an API key in the page. Is that a problem?#

Yes, because anyone who opens the page can copy it. A deploy whose files contain a secret key is stopped and says which file and line. Ask your AI to move the call into a function and to open the box for the key.

What if my app suddenly gets many more users?#

It keeps running and is billed at cost from your balance. There is no plan to outgrow. Turn on automatic top-up so the paid parts never pause when the balance runs low.