Replit

Replit Agent 3 sits somewhere between a code assistant and a junior developer who never sleeps. You describe an app in plain English, it spins up a sandbox, writes the code, tests it, debugs failures, and deploys a live URL. The autonomy is real: I asked it to build a markdown preview tool with live syntax highlighting, walked away for coffee, and came back to a working prototype with a shareable link. No babysitting, no copy-paste dance between chat and editor. The killer feature is the integrated sandbox. Agent 3 doesn't just generate code, it runs it, sees errors, and fixes them without asking permission. When a dependency failed to install, it switched package managers on its own. When the UI looked broken on mobile, it rewrote the CSS after testing in the preview pane. This closed-loop iteration is what separates it from Cursor or Copilot, which still need you to spot problems and prompt corrections. It shines for throwaway prototypes, internal tools, and learning projects. I used it to mock up a webhook receiver for a Slack integration in under ten minutes. The code wasn't production-grade, but it worked well enough to validate the idea before committing real engineering time. For solo founders or product managers who can read code but don't write it daily, this is transformative. Failure modes: it struggles with complex state management and anything requiring external APIs with tricky auth flows. I tried building a multi-step form with conditional logic, and it produced a tangled mess of useState hooks that I had to refactor by hand. It also has no memory between sessions, so iterating on the same project over days means re-explaining context. Compared to Lovable or Bolt, Replit's agent is faster but less polished for design-heavy apps. Bolt produces prettier UIs out of the gate; Replit prioritises functional code over aesthetics. The free tier is generous, three AI generations per day, but serious use demands the $20/month plan for unlimited builds and better compute. Hosting is included, which undercuts Vercel's pricing if you're deploying multiple small projects. The mobile app is surprisingly capable for reviewing builds on the go, though you'll still want a proper keyboard for any real editing.