I built my own AI reply system for Twitter & LinkedIn (and ended up turning it into a SaaS starter kit)

A few weeks ago I wanted something simple: an AI tool that could help me generate replies on Twitter and LinkedIn.

But I didn't want to rely on random SaaS tools or send my data to third‑party services.

So I built a small system for myself:

• A browser extension to generate replies

• A Node.js backend to handle AI calls

• A writing persona engine so responses stay consistent

• Redis + MongoDB for caching and storage

Over time it turned into a full stack setup:

Extension → Backend → AI Provider

I also added:

• TXT based writing style profiles
• User onboarding preferences
• Support for Twitter and LinkedIn reply generation
• A small dashboard to manage persona settings

The funny part is that I still run it locally on my machine.

A few dev friends asked if I could share the code, so I packaged it into a starter kit for anyone building AI tools or extensions.

Curious what others here would build with something like this.