You have an app idea. You also have ten tabs open, a half-written prompt to ChatGPT, and no idea if the idea is even good yet.BuildBrief fixes that. It's four prompts, run in order, in whatever AI chat tool you already use. No new software, no account, no subscription. Just a single file that walks you from "I have an idea" to "I have a build prompt and a 48-hour launch plan" in about 15 to 20 minutes.How it works1. Copy a stage's prompt and paste it into a fresh chat in ChatGPT, Claude, Lovable, Bolt, Replit, or Cursor.2. The AI responds. You paste that response into BuildBrief's matching tracker box.3. The next stage's prompt automatically fills in with your real answers, no retyping, no hunting for what you wrote three tabs ago.4. Repeat through all four stages. You end up with a validated idea, a screen list, a ready-to-paste build prompt, and a day-by-day launch plan.The four stages- Idea Validator: scores your idea 1 to 10 across six factors (pain intensity, audience clarity, willingness to pay, competition, build simplicity, recurring use) and gives you an honest verdict, including "don't build this yet" when that's the truth.- Screen Blueprint: turns a validated idea into the smallest possible screen list (six screens, max), plus a plain-English data model. No login screens or settings pages you don't need yet.- Prompt Builder: generates one ready-to-paste build prompt, with a version for no-code tools (Lovable, Bolt, Replit) and a separate version for code agents (Cursor, Claude Code).- 48-Hour Launch Plan: a half-day-by-half-day checklist covering the build, testing on a real device, pricing, a landing page, and the actual publish step.Every stage includes a real worked example (a storm-damage roofing app called RoofDoc) so you can see exactly what a good answer looks like before you write your own.What's included- One self-contained HTML file. Double-click it, it opens in any browser.- A progress tracker that saves your answers as you type.- Export and Import buttons, so your progress travels with you if you move the file or switch computers.- No account, no install, no recurring fee. It's yours.Who this is forSolo builders and indie hackers who want to stop guessing whether an idea is worth a weekend, and start with a plan instead of a blank chat window.A couple of things worth knowing- This is a workbook, not an app. It doesn't call any AI on your behalf, you paste its prompts into the AI tool of your choice.- For best results, open it in Chrome or Firefox. Safari restricts local file storage more aggressively, so your saved progress may not stick between sessions there.