I use them successfully on larger project all the time.
"Here's some example JavaScript code that sends an email through the SendGrid REST API. Write me a python function for sending an email that accepts an email address, subject, path to a Jinja template and a dictionary of template context. It should return true or false for if the email was sent without errors, and log any error messages to stderr"
That prompt is equally effective for a project that's 500 lines or 5,000,000 lines of code.
I also use them for code spelunking - you can pipe quite a lot of code into Gemini and ask questions like "which modules handle incoming API request validation?" - that's why I built https://github.com/simonw/files-to-prompt
"Here's some example JavaScript code that sends an email through the SendGrid REST API. Write me a python function for sending an email that accepts an email address, subject, path to a Jinja template and a dictionary of template context. It should return true or false for if the email was sent without errors, and log any error messages to stderr"
That prompt is equally effective for a project that's 500 lines or 5,000,000 lines of code.
I also use them for code spelunking - you can pipe quite a lot of code into Gemini and ask questions like "which modules handle incoming API request validation?" - that's why I built https://github.com/simonw/files-to-prompt