EI-301d · Module 3

Decision Documentation Standards

3 min read

Every build-vs-buy decision should produce a decision record that future teams can reference. The decision record answers: what decision was made, why, what alternatives were considered, what assumptions drove the decision, and what conditions would trigger a re-evaluation. Decision records create institutional memory that prevents the organization from revisiting the same decision every time a new leader arrives or a new vendor appears.

Do This

  • Document the ecosystem trajectory assumptions behind the decision — these are the assumptions most likely to invalidate the decision as the ecosystem evolves
  • Specify re-evaluation triggers: "Re-evaluate if vendor pricing exceeds $X" or "Re-evaluate if open-source alternative reaches Y% parity"
  • Archive the decision record alongside the TCO model and vendor scorecard — future reviewers need the full context

Avoid This

  • Document only the decision without the reasoning — future teams cannot evaluate whether the decision is still valid without understanding why it was made
  • Omit the alternatives considered — future teams may waste time evaluating options that were already rejected for documented reasons
  • Skip documentation for "obvious" decisions — obvious decisions are the ones most likely to be second-guessed later when context has been forgotten

The re-evaluation trigger is the most valuable element of the decision record. It specifies the exact conditions under which the decision should be revisited. "Re-evaluate if inference costs decline below $0.002 per 1K tokens" is a trigger that ecosystem monitoring can automatically track. When the trigger fires, the decision record provides the context for an informed re-evaluation rather than starting from scratch.