You're a solo founder or small team and your signup count could jump overnight — a front-page Hacker News or Product Hunt day.
Tools billed per contact, per lead, or per email turn a good launch into a bigger invoice, and some waitlist APIs are gated behind a paid tier entirely.
Pricing is capacity, not throughput — signups stored, not signups per month. Nothing is metered on any tier, including free, so a spike changes nothing about the bill.
A real API key, the MCP server, and signup emails — no credit card.