Try ten directions. Commit to one.
Your riskiest weeks are the ones spent building the wrong thing. On this canvas you describe an idea and get a working version in minutes, so you can put three takes in front of users tonight and commit with evidence. The agent you already subscribe to does the building.
Validate the day you have the idea
Describe the screen and a running version appears. What you learn is real because the prototype is.
Put three takes in front of users tonight
Branching costs a sentence. Keep the one people actually use.
Demo the product, not the deck
Investors and early users click a working slice, typed input and all.
No engineering hire to test demand
Claude Code, Codex, or Cursor builds on your canvas, on the subscription you already pay for.
The validated prototype becomes the product
Real React from day one. When something wins, you keep building on it instead of rebuilding it.
The meter you are currently feeding
If you are validating a startup idea with an AI app builder today, you know the rhythm. Type a prompt, wait, get a result that is 70 percent right, and pay again to fix the 30 percent. Chat-first tools charge per generation, so every “actually, make the sidebar collapsible” has a price tag, and exploring a second direction doubles it. You start economizing on curiosity, which is exactly the wrong thing for a founder to ration.
The other version of this trap is slower: no technical cofounder, so the idea waits on a contractor’s calendar, and by the time the build lands you have spent a month and a few thousand dollars learning something a working afternoon could have told you.
Exploration without the meter
Prototyper connects the coding agent you already subscribe to, Claude Code, Codex, or Cursor, to an infinite canvas. Bring your own agent means the building happens on the flat-rate plan you are already paying for, so iteration stops being a billing event. Ask for a marketplace with three different onboarding flows and you get three running apps side by side. Ask for ten changes and the only cost is the time it takes to look at them.
Because the prototypes run, your validation is honest. Users type into real inputs and hit real states instead of tapping through a slideshow, and investors click the product in the meeting rather than watching a screen recording of one. A demo that survives someone else’s hands is a different class of evidence.
When one direction wins, you do not start over. The winner is real React on a real file system, and the same agent that built it keeps building: more screens, real data, the road to launch. The prototype is the product, so validation and construction are the same work.
A concrete first week
Day one: describe the core screen and get it running, then branch two more takes on the idea. Day two: put all three in front of ten people and watch where they hesitate. Day three: kill two, tell the agent what the survivors taught you, and let it deepen the winner. By the weekend you have a working slice, user evidence, and a codebase, and you have written no code and hired no one.
Where you will spend your time
Bring your own agent over MCP. Your existing subscription is the build engine.
The canvasIdeas, variants, and working apps arranged side by side, so comparison is a glance.
Live previewPrototypes run with real inputs, so user tests and investor demos hold up to touch.
CollaborationSend one link. Advisors, users, and cofounders see the live canvas as free viewers.
When Prototyper is not your tool yet
A working product slice is not the whole company. Production concerns like payments, authentication at scale, and heavy backend infrastructure still deserve engineering attention when real customers depend on them, whether that engineering is a hire, a contractor, or your agent under closer supervision.
Prototyper gets you to the moment where that investment is justified by evidence instead of hope, with a real codebase to continue from rather than a mockup to throw away.
Frequently asked questions
- I have no technical cofounder. Can I use this?
- Yes. You describe what you want in plain language and steer by pointing at what comes back. The agent handles the code. Founders ship working slices here without writing any.
- Is the output real code or a demo toy?
- Real React, running in the browser. The code behind your prototype is the same code you would take to production, and you can hand it to an engineer or an agent to keep going.
- What does it cost to run the agent?
- Prototyper is free to start. The building is done by the agent subscription you already have, Claude Code, Codex, or Cursor, connected over MCP. No separate API bill.
- How is this different from v0 or Lovable?
- Those are chat windows that charge per generation and hand you output to take elsewhere. Prototyper is a canvas where your own agent builds, iteration is free once you bring your subscription, and the work stays in a workspace that runs.
- Can I export the code?
- Yes. Everything on the canvas is a real file tree. Take it to a repository whenever you want; nothing is locked to our hosting.
See it with your own work.
Free to start, no credit card. Bring the agent you already have.