Sustainability-linked bonds (SLBs) embed sustainability commitments directly into debt contracts, but the credibility of these commitments depends on how penalties, reporting obligations, and verification requirements are written and enforced. We construct bond-level measures of contractual enforceability and target precision from SLB frameworks, prospectuses, and performance-target documentation for 915 SLBs, and link them to secondary-market Z-spreads and to matched conventional bonds from the same issuer or corporate parent. Three findings emerge. First, the basic contractual architecture has become nearly universal: 92% of SLBs contain penalty-activation, reporting, and external-assurance provisions. […]