Solo Dev Builds 35-Module Household SaaS with Claude — Workflow Deep Dive

A senior engineer with 25 years in engineering leadership launched Kaevo (kaevo.ai), a household operating system covering finances, home maintenance, travel, family records, and estate docs — all built solo over several months using Claude as his engineering partner. The stack: Vite + Netlify + Supabase + Stripe billing, roughly 35 modules. This is a build-story post focusing on the workflow that made it possible.

The Workflow That Worked

Three key patterns emerged:

• Investigation-first, not code-first. The highest-value prompt pattern wasn't "write this function" but "trace how this data flows and tell me where it breaks before proposing anything." In the final pre-launch week, this caught a silent-charge risk in Stripe (abandoned checkouts would have auto-billed at day 14 with no account attached) and data-loss bugs where documents with undefined IDs silently overwrote each other in the document vault. Quick-patch prompting would have missed all of it.
• Test-first on money paths, enforced. Stripe webhooks, subscription state, billing logic — all pure predicates with unit tests written red-first before any I/O. The test suite gates the deploy, so nothing ships on a red build.
• Claude pushed back. More than once Claude Code refused to "fix" something after investigating and finding the bug didn't exist in current code — including a suspected account-deletion cascade that had been fixed months earlier. An agent that fabricates fixes for phantom bugs is worse than useless on a money path.

Division of Labor

• claude.ai drafted specs and triaged
• Claude Code investigated and executed
• Human verified everything on the live site and applied all schema changes manually. Human gate on anything touching production data or money; full autonomy on investigation and test-covered code.

Honest Limitations

• Claude occasionally pattern-matched to the wrong diagnosis before investigating — the discipline of forcing investigation first was the developer's to enforce.
• Long sessions needed deliberate context management.

Net result: what would have taken a small team a year took a few months solo. There's a free interactive demo on the site (no signup needed) if you want to poke at what got built.