I’m working on a project called Injectless — a browser extension that allows websites to explicitly declare which data they are allowed to inject into external sites, fully controlled by the user.

Note: This post was translated to English using AI. My native language is Spanish.

The Problem: Users of SaaS apps (accounting, project management, etc.) often need to repeatedly copy data into external forms (government portals, client systems, etc.). Today this is a tedious, fully manual process.

My Current Solution A browser extension where: - Websites expose an injectless.json declaring which fields they can fill and on which domains - The user explicitly installs the integration (one-click opt-in) - When visiting an allowed site, the extension offers to “paste” each field

The Doubt A friend suggested that instead of a browser extension, this should be a native app (similar to KeePassXC or Espanso) that: - Works in any browser without installing multiple extensions - Pastes sequences of fields using TAB (simpler, more universal) - Works even outside the browser - Avoids extension permissions, CSP issues, Shadow DOM, etc.

My Concerns About a Native App - Mobile: Browser extensions do work on mobile (Safari iOS, Firefox Android). Native apps would face heavy sandboxing restrictions - UX: The extension popup can show exactly which fields are available for the current page. A native app would be more “blind” - Context: The extension knows which page you’re on and can automatically validate allowed domains

The Question What seems more valuable / practical? A) Browser extension (current approach) — more context, mobile support, clearer UX B) Native app like Espanso/KeePassXC — more universal, single install, simpler C) Both — native app as a base + optional extension as a companion for better UX

Has anyone worked on something similar? What trade-offs might I be missing?

Thanks!