TL;DR - The single biggest thing that unlocked AI coding for me wasn't a better prompt. It was running a full production simulation on localhost so the agent can see the software running, not just read the code.
The problem
When an AI agent can only see your source code, it's coding blind. It writes something and hopes it works. But an app isn't one file. It's a set of parts (frontend, backend, database, APIs) talking to each other, and the real bugs live in how those parts connect, not in any single file. If the agent can't run the thing, it can't see where it actually breaks.
What I did
I run every part of the app locally, on localhost, and give the agent access to it. That changes everything.
- It can run the app and click through it.
- It can hit the API and read the real responses.
- It can read the real errors and logs.
- It can see the actual behavior, not a guess about it.
From there it writes tests, catches the bugs, and fixes them against the real, running system. It closes the loop instead of shipping hopeful code.
The result
The workflow speed-up is dramatic. Once the agent can observe the software actually running, it stops guessing and starts verifying, and the amount of back-and-forth to get something correct drops sharply.
The lesson
Fully leveraging an AI agent isn't about clever prompts. It's about giving it the running system to work against. Run it all locally, hand the agent the keys, and let it see reality. That's the unlock most people skip.
Stack - local dev servers (localhost), Playwright MCP, Claude / Fable.