We asked Claude Code (opus-4-8) to build the same growing SaaS app three ways, three times each: with Fonderie, with our full skill loaded, and from scratch with no Fonderie knowledge. 36 sessions total.
The from-scratch runs:
- Reinvented auth, billing, and permissions every single time (different schemas, different API shapes)
- Hardcoded a JWT secret in 2 of 3 runs
- Burned ~3× the tokens per turn
The Fonderie runs:
- Reached for pre-built, audited bricks instead of improvising
- Zero hardcoded secrets (the brick throws if env vars are missing)
- ~⅓ the code, ~⅓ the context-window pressure
Fonderie is an open-source backend skill for AI coding assistants. Instead of letting your LLM re-derive auth, Stripe billing, workspaces, and RBAC from scratch every session, you give it a standard mold it already knows.
One command:
npx create-fonderie-app my-saas
Then tell Claude: "Add billing." It installs @fonderie/billing, wires the routes, and moves on to your actual product.
MIT licensed. No seats, no rent. The benchmark harness and raw transcripts are in the repo.
Repo: https://github.com/fonderiejs/fonderie
Docs: https://fonderiejs.com
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