I’ve been shipping Ja-ti, a small product that tracks follower changes on X: who followed, who left, and the messy middle (suspended accounts, “gone” profiles, that sort of thing). The pitch fits on a line — know who arrives, know who leaves — but the implementation is where it gets interesting, because “compare two follower lists” sounds trivial until you’re doing it repeatedly, fairly across subscribers, within API and platform limits, and with billing that matches how expensive an account actually is to track.
At a high level, Ja-ti takes the accounts you care about and checks them on a cadence you choose (within feasibility rules driven by audience size — you can’t promise a 15-minute sweep on a seven-figure follower count and mean it). It stores snapshots and diffs so you see history, not just a one-off delta. It sends digest email when something changed: new follows, unfollows, VIP-tier movements, account-status shifts — with tier-aware truncation so the entry experience doesn’t pretend every account gets a novel.
Billing is usage-shaped: list price scales with follower-count bands, there’s a card-required trial, and manual checks are gated differently from automatic runs so power users don’t accidentally erode margin. None of that needs a manifesto; it’s the boring truth of consumer infra products — the price has to track the cost, and the UX has to fail loudly when someone asks for the impossible.
