Every AI coding agent demo looks like magic. Clean UI, working app, thirty seconds flat. Then you paste your own prompt, hit run, and stare at a broken build with hallucinated imports and an auth flow that references packages that don’t exist.
I ran the same project spec through Replit Agent, Bolt, and v0 to find out which one actually ships working code. The results weren’t close.
The Test: Same Prompt, Three Tools, One Question
The spec: a task management app with authentication, CRUD operations, and a basic dashboard. Nothing exotic. The kind of project every AI app builder should handle without breaking a sweat.
I measured three things. Time to first working build. Total cost to get a shippable app. Number of broken iterations before something actually ran.
No hand-holding. Each tool got the same natural-language prompt and had to figure out architecture, dependencies, and deployment on its own. The prompt was roughly two paragraphs — detailed enough to be clear, vague enough to test how each tool fills gaps.
Simple spec. Three autonomous coding tools. One question: which one choked?
What Each Tool Actually Did With the Same Prompt
Replit Agent went fully autonomous. It scaffolded a full-stack app, picked its own framework, and started iterating. Impressive for about four minutes. Then it hit a doop loop on the auth integration — cycling through the same fix attempt over and over, burning compute without making progress. Twenty-plus minutes of this before I intervened manually.
The app eventually worked, but “eventually” included me stepping in to break the loop and pointing the agent at the right dependency. Replit’s effort-based pricing, which replaced flat-rate requests in mid-2025, meant the cost was unpredictable. The $25/month Core plan doesn’t tell you what a complex prompt will actually cost until it’s done running.
Bolt.new generated a full app fast. First impression: this might actually work. Second impression: the build failed. Hallucinated Supabase imports. A broken auth flow referencing a table structure that didn’t match the actual schema.
The error loop consumed roughly 3-4 million tokens before a working version emerged. If you’re on the $20/month Pro plan with 10 million tokens, that’s a third of your monthly budget on a single app’s debugging cycle. Bolt’s Discussion Mode helps you troubleshoot before burning tokens on rebuilds, but most users don’t discover it until they’ve already torched their allowance.
v0 did something different. It produced clean React and Tailwind frontend code in under a minute. Beautiful components. Proper structure. Production-ready markup.
And absolutely nothing else. No auth. No database. No API routes. v0 is frontend-only, and it doesn’t pretend otherwise — but if you came in expecting a full-stack app builder, you’ll leave confused and empty-handed. For pure UI scaffolding, though, nothing in this test touched it.
The uncomfortable truth: none of them shipped a complete, working app on the first attempt. But the ways they failed reveal exactly which one fits your situation.
The Real Cost to Ship (Not the Sticker Price)
Pricing pages lie by omission. Here’s what the test actually cost.
Replit Agent: $25/month base, but effort-based pricing means your bill scales with complexity. A real project with iteration and debugging runs $30-50. The doop loops don’t just waste time — they waste the compute you’re paying for.
Bolt: $20/month gets you 10 million tokens. Sounds generous until error loops burn 3-5 million on a single app. If you’re building anything with auth or database integration, budget $50-100/month realistically. Tokens don’t roll over, so a bad week erases your cushion. The solo founder AI stack math changes fast when token drain is real.
v0: $20/month is the most predictable price here. But you’re only getting frontend. Add your own backend development time, hosting costs, and the hours connecting v0’s output to actual infrastructure.
The math nobody does: factor in your debugging time at your hourly rate. The “cheapest” tool on paper might be the most expensive tool in practice.
So knowing what these things really cost and how they really perform — which one should you actually use?
Which One to Use (Based on What You’re Building)
Building a quick UI prototype? v0. It does one thing and does it exceptionally well. Stop expecting full-stack from a frontend tool and it becomes the fastest path from idea to visual prototype. Pair it with your own backend or a tool like Cursor for the rest.
Building an MVP you need to demo next week? Bolt. Budget for token overages and expect to fix auth manually. The speed of first output is genuinely impressive — you just need to account for the debugging tax.
Building something you’ll iterate on for months? Replit Agent. The full IDE environment, multi-language support, and autonomous iteration pay off over time. The learning curve and occasional doop loops are the price of a tool that grows with your project.
The demos lied about ease. None of these vibe coding tools are magic — you won’t paste a prompt and get a production app. But they genuinely cut build time from weeks to days if you pick the right one for your use case.
The best AI coding agent is the one whose failure mode you already know how to fix.