Think about when you actually need an API key. You're on a provider's dashboard creating a new key. You're building something locally and need to paste a key into a form or a config file. You're rotating a key and need to update your .env. In almost every case, you're in a browser.
The gap with existing tools: you're in one tab and your key is somewhere else. A password manager requires you to open it, search, find the entry, copy the value — multiple context switches just to grab a credential. A text file requires you to open a different app. Notes apps, Notion, Slack — all require leaving your current context.
A Chrome extension solves this at the right layer. It's in the browser, where the task is happening. It can observe which site you're on and filter the vault automatically. One click, key copied, back to work. That's the workflow improvement that makes a browser-based approach worth it.
The tradeoff is that extensions are Chrome-only (API Locker currently supports Chrome and Chromium-based browsers). But for most developers, Chrome or Brave is their primary development browser — and the productivity gain at that layer outweighs the limitation.