Building a Shopify app with Claude Code — spec-driven development and pricing design

This is part 3 of a series on building MetaBulkify, a Shopify app for bulk editing metaobjects via CSV. Part 1: Excel data corruption and GID/handle resolution Part 2: Shopify platform traps (scopes, throttling, dev store billing) This post is about two things: how I build software as a solo developer with AI, and how I designed pricing to let users try the app properly before committing. How I actually build things I have a day job. I code side projects on evenings and weekends. Time is the scarcest resource. My workflow: I write detailed spec documents, then delegate implementation to Claude Code. Not prompts. Not “build me an app.” Actual specs — 200+ line instruction documents covering data models, edge cases, error handling, security considerations. Then Claude Code writes the code, and I review every line. This is not “AI wrote my app.” I make every architecture decision: Which GraphQL mutations to use How billing works Where to put the usage tracking table What happens when Cloud Tasks retries a failed job Whether to fail-open or fail-closed on API errors Claude Code is a fast pair programmer who never gets tired and never pushes back when I ask for a third rewrite. What a spec doc looks like For the billing system, my spec included: A plan comparison table (Free vs Pro, exact limits) Prisma schema for the usage tracking table The exact GraphQL query for subscription detection Error handling rules (fail-closed, count attempts not successes) Idempotency requirements (Cloud…

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