Not every agency pronouncement is a "rule" subject to the APA's full notice-and-comment process. The APA distinguishes substantive rules — which create new legal obligations or rights with the force of law — from procedural rules governing agency organization or process, interpretive rules that merely clarify existing law, and general statements of policy that announce an agency's future enforcement or discretionary approach without binding effect.

The classification matters enormously in practice: only substantive rules generally require the notice-and-comment process, so an agency that wants to avoid the time and political exposure of public comment has an incentive to characterize a new requirement as merely interpretive or a policy statement. Courts scrutinize this classification by looking past the agency's label to the rule's actual legal effect — a document that in practice binds regulated parties or agency staff as if it had the force of law, leaving no real discretion in application, risks being recharacterized as substantive regardless of how the agency labeled it.

A Juricratic simulation of a challenge to an agency guidance document can model the substantive-versus-interpretive classification as a threshold dial that determines which procedural-defect theories are even available — a matter framed around a document a court is likely to treat as substantive opens up a much larger notice-and-comment-based challenge space than one likely to be treated as genuinely interpretive.

Counsel challenging agency guidance evaluates whether the document functions, in practice, as a binding legal requirement rather than genuine interpretation or discretionary policy, since a strong argument that the agency mislabeled a substantive rule as interpretive or procedural can open a notice-and-comment-based challenge that would otherwise be unavailable.