StartupENGINEERING
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Decision skill · FreeProduct Loop

Build on a platform or build custom?

Should your product be built on an existing platform or built custom — and what does each choice lock in?

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Version 1.0 · Plain text · No email required · CC BY-SA 4.0

What this skill does

Hand this file to Claude or ChatGPT. The assistant interviews you, one question at a time, through this decision's determining questions — on your specifics. It then applies the decision rules to your answers and gives you the recommendation plainly, with the conditions under which it would change.

The decision it executes
Build on a platform or build custom? →

Shopify-or-custom, Salesforce-or-custom, wire-together-or-build: what platform choices really cost over two years, and which lock-ins are cheap to escape versus permanent.

The guide is the canonical version: determining questions, paths with dated costs, what I'd do, and limits. It belongs to The Product Loop.

Escalation clause
An honest tool knows its edges.

This decision stops being self-serve — and needs a human with scars in the room — when:

  • The product IS infrastructure (an API, developer tool, or platform itself) — there is nothing to buy; this framework does not apply.
  • A compliance regime (healthcare data, payment-card scope, financial audit requirements) dictates where data lives and how it moves — the compliance analysis decides the architecture, not cost math.
  • The product must integrate deeply with a legacy system a customer or partner already runs — that system's constraints decide what is buildable.
  • The two-year totals across paths are close enough that the decision hinges on technical judgment about the platform's extension limits — that judgment needs a human who has built on that platform.
When this skill revises
Optional. The download never depends on it.

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