The decisive variable for tool linkability — citable PUBLIC output, not code quality

Claim: Practitioner analysis stresses that tools built around a public number other writers need to quote earn links, whereas "the overwhelming majority of free calculators published this year will finish their first year with single-digit referring domains."

Source: Link-building vendor analysis. Flagged as vendor-originated but directionally credible precisely because it documents the FAILURE base rate.

Confidence: Single-source / Directional.

Why this matters for Candid: Threshold below which Tier 3 is not worth building — if the tool does not produce a uniquely citable, reusable output that fills a real "citation need," it will not earn links. This matches the existing KB rule R4 — When SEO is part of the case, build for CITATION not just utility — the public quotable number earns the links; the private personal answer does not (the R4 rule from the earlier interactive-tool-mechanisms brief).