buy-vs-build

Use when evaluating whether to adopt a specific open-source or commercial dependency (npm/PyPI/etc. package or library) — to research its fit, maintenance and health, security and supply-chain risk, license, and footprint before taking it on.

Use when reviewing a code diff, pull request, or local changes for buy-vs-build mistakes, avoidable custom code, unnecessary dependencies, missed built-ins, missed platform features, or weak decision notes.

Use when choosing between options at the same ownership rung — a transport, API style, data store, job/async mechanism, integration pattern, or cache — and you want the one that fits the requirement's real shape (directionality, volume, latency, consistency, failure mode) rather than the most powerful, popular, or familiar default.

Use when coding, designing an implementation, choosing dependencies, adding features, reviewing diffs for custom code, evaluating whether to use built-ins, standard libraries, native platform features, installed packages, open source libraries, commercial services, or an in-house implementation.

Use when a non-obvious buy-vs-build decision was just made and should be recorded durably, or when a project keeps a docs/decisions/ log of Architecture Decision Records (ADRs) for build/buy/reuse and dependency choices.

Use when choosing between built-ins, standard libraries, native platform features, installed packages, open source libraries, commercial products, or in-house implementation for a feature or technical design.

Use when coding, designing implementations, choosing dependencies, or reviewing whether a task should use built-ins, platform features, installed packages, open source, commercial services, or in-house code.

Use when auditing a repository or subsystem for avoidable in-house implementations, unnecessary dependencies, duplicated platform features, vendor lock-in, maintenance burden, or unclear buy-vs-build ownership decisions.

Use when summarizing Buy vs Build benchmark cases, behavior measurements, expected impact, release notes, or evidence that the ruleset reduces unnecessary code, dependencies, cost, or ownership risk.