Do I need a mobile app or a responsive website?

You need a responsive website. You might also need a mobile app, but probably not yet.

A responsive website works on every device with a single codebase. It's indexed by search engines, shareable via URL, doesn't require app store approval, and costs 3-5× less than a native app. For 90% of B2B operators, a fast responsive site handles everything: information, lead capture, customer portals, and even real-time features.

You need a native app when: your users need offline functionality, you require hardware access (camera, GPS, push notifications at system level), you need background processing, or your product IS the app (a game, a tool used 30+ minutes daily). You don't need a native app for a brochure site, a blog, or a lead generation form.

The middle ground is a Progressive Web App (PWA) — a responsive website that can be installed on the home screen, work offline, and send push notifications. PWAs work on both iOS and Android, cost the same as a website to build, and avoid app store gatekeeping.

The build-an-app-first instinct burns more startup capital than any other technical decision. Build the website first. Add the app when usage data proves the investment.