Copilot vs Claude Code vs Cursor for real projects. Spec first workflow made the biggest difference

I have been using GitHub Copilot daily in VS Code and I kept seeing the same pattern. Copilot feels great for small changes and quick fixes but once the task touches multiple files it can drift unless I am very explicit about what it can change

So I did a simple project based comparison on a small but real codebase. a Next app plus an API service with auth rate limiting and a few background jobs. Nothing huge but enough moving parts to expose problems. I tried Copilot Chat with GPT 5.3 and also GPT 5.2. I tried Claude Opus 4.6 through Claude Code. I also tried Cursor with the same repo. For curiosity I tested Gemini 2.5 for planning and DeepSeek for some refactor grunt work

The surprising result. the model choice mattered less than the workflow

When I went prompt first and asked for a feature in one go. every tool started freelancing. Copilot was fast but sometimes edited files I did not want touched. Claude Code could go deeper but also tried to improve things beyond the ask. Cursor was good at navigating the repo but could still over change stuff if the request was broad

When I went spec first everything got calmer. I wrote a one page spec before any code changes. goal. non goals. files allowed. API contract. acceptance checks. rollback rule. I used Traycer AI to turn my rough idea into that checklist spec so it stayed short and testable. Then Copilot became way more reliable because I could paste the spec and tell it to only implement one acceptance check at a time. Claude Code was best when the spec asked for a bigger refactor or when a bug needed deeper reasoning. Cursor helped when I needed to locate all call sites and do consistent edits across the repo. I used ripgrep and unit tests as the final gate

My take is Copilot is not worse or better than the others. It is just optimized for the edit loop and it needs constraints. If you give it a tight spec and make it work in small diffs it feels very strong. If you ask it to build the whole feature in one shot it becomes a dice roll

How are you all running Copilot in larger projects. Do you keep a spec file in the repo. do you slice specs per feature. and do you prefer Copilot for the implement phase and another tool for planning and review