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API marketplace

Zevium

Backend systems for an API marketplace, from a payment migration to a credit-based usage system built for heavy writes.

The Zevium landing page in dark mode, explaining pay-per-call APIs.
Buys 10,000 credits for pay-per-call APIs
$1
Of each charge goes to the API publisher
95%
Charges for failed calls; credits are spent only on success
0
Role
Backend engineer
Period
Nov 2025 – Apr 2026
Stack
TanStack Start, TypeScript, Cloudflare Workers, Redis, SQLite
Live
zevium.dev ↗ (opens in a new tab)

Overview

Zevium is an API marketplace where developers and agents pay per call. I built its backend systems.

Payments and credits

I migrated the payment flow from Autumn to Polar and integrated secure billing. On top of it, I designed a credit-based usage system: users buy credits and spend them as they call marketplace APIs.

The write problem

Usage produces far more writes than reads, because every call is a transaction to record.

  1. 01API call
  2. 02Redis (real time)
  3. 03Worker cron
  4. 04SQLite (batched)

Transactions are recorded in Redis as they happen. A Cloudflare Worker cron job then persists them to SQLite in batches, which keeps the serverless setup cost-efficient as usage grows.

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