The Source-Locked Verification skill forces Claude into a strict evidential-fidelity mode where it can only answer from two sources: materials you provide, and online sources it has actually accessed during the task. It cannot infer, assume, estimate, generalise, or fill gaps — if something isn’t expressly stated in the evidence or a verified source, Claude must say so rather than fabricate a plausible-sounding answer.

The skill is built around 19 mandatory rules covering the full range of ways Claude might otherwise drift from the evidence. The core rules prohibit unsupported inferences (if a document says “April”, Claude cannot say “1 April”), invented citations (no fabricated case names, paragraph numbers, dates, or quotations), and false confidence language (“clearly”, “obviously”, “it follows that”) unless the point is expressly sourced. Every material claim must be anchored to a pinpoint reference — document name plus page, paragraph, clause, URL, or quoted excerpt.

The skill requires Claude to categorise every statement into one of five tiers: expressly stated in your materials, expressly stated in a verified online source, supported but not expressly stated (used sparingly, with reasoning shown), not found, or possible inference (only if you’ve asked for inferences). This lets you instantly assess how much weight to give each point.

For legal work specifically, the skill enforces a source hierarchy prioritising legislation.gov.uk, BAILII, official court and regulator sources, and primary authorities over secondary commentary. It requires Claude to verify appellate history, check whether legislation is still in force, and confirm procedural rules online rather than stating them from background knowledge. When sources conflict, Claude must flag the conflict rather than resolve it by assumption.

The skill includes a structured answer template (answer, source basis table, sources checked, points not found, and limited inferences if requested), a 12-point self-check checklist Claude must run before delivering any response, and a refusal protocol — if you ask Claude to state something the evidence doesn’t support, it will tell you what the evidence does support instead of inventing backing.

It’s designed for legal, factual, research, evidence review, document review, citation-checking, chronology, and drafting tasks — anything where you’re relying on Claude’s output as a faithful representation of what the sources actually say.