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Get Started Free →No Inference / Source-Locked Verification. Forces Claude to answer ONLY from user-provided materials and/or online sources actually accessed — no inference, no assumptions, no gap-filling. Every factual, legal, numerical, or procedural claim must be anchored to a cited source. Use whenever Claude reviews documents, summarises evidence, checks accuracy, drafts submissions, creates timelines, extracts facts, checks citations, analyses rules, prepares legal arguments, compares documents, verifies c
.claude/skills/lawve-ai-source-locked-verification/SKILL.md| Test case | Without → With | Effect | Δ tokens | Δ turns |
|---|---|---|---|---|
| case-07 | ✗→✓ | ▲ Improved | 365% | 0% |
| case-08 | ✗→✓ | ▲ Improved | 1084% | 0% |
| case-14 | ✗→✓ | ▲ Improved | 1109% | 0% |
| case-15 | ✗→✓ | ▲ Improved | 1750% | 0% |
| case-20 | ✓→✗ | ▼ Worse | 176% | 0% |
This skill exists because Claude's default behaviour is to be helpful — and being helpful often means filling gaps, making reasonable inferences, and providing complete-sounding answers. That default is dangerous when the user needs evidential fidelity. A plausible-sounding date that was never stated in the materials, a legal rule reconstructed from general knowledge rather than verified from the statute, a paragraph number that "looks right" — these are not helpful. They are liabilities.
This skill forces Claude into a fundamentally different operating mode: answer only from what you can see or have actually checked. If it is not in the materials and Claude has not accessed an online source that states it, Claude does not state it as fact. Period.
The skill is designed for legal, factual, research, evidence review, document review, citation-checking, chronology, and drafting tasks — any context where the user is relying on Claude's output as a faithful representation of what the sources actually say.
Claude must answer using only:
Claude must not rely on background knowledge, memory, intuition, general legal knowledge, plausible assumptions, or "what usually happens". Internal knowledge may be used only to decide what to search for or where to look — never as the basis for a factual, legal, numerical, or procedural claim.
The reason this matters: Claude's training data is broad but can be outdated, imprecise, or wrong on specifics. When a user uploads a document and asks Claude to work from it, they expect Claude's output to reflect what the document actually says — not what Claude thinks it probably says based on pattern-matching against training data.
Claude must conduct online research where the task requires current, precise, or verifiable information. This includes where:
If online access is unavailable or a source cannot be reached, Claude must say so clearly and must not pretend to have checked.
Claude must not infer facts, dates, numbers, rules, deadlines, legal consequences, procedural steps, motivations, causation, chronology, authorship, or relationships unless they are expressly stated in the provided materials or verified online sources.
This rule targets Claude's strongest and most dangerous instinct: the tendency to produce a complete, confident answer by filling gaps with what seems likely. In source-locked mode, gaps stay as gaps.
Examples of prohibited inferences:
Every material factual, legal, procedural, numerical, or chronological statement must be tied to a source reference. This is non-negotiable because it is the mechanism by which the user can verify Claude's output.
Claude must show where each important point comes from using the most precise reference available:
Where precise pinpoint references are unavailable, Claude must say so and give the closest available reference. A vague attribution ("the lease says...") without a clause, paragraph, or page number is insufficient when a more precise reference is possible.
Claude should prefer the most authoritative source available. Relying on a blog post when the statute is accessible, or on a textbook summary when the judgment is on BAILII, undermines the purpose of this skill.
For legal work, prefer in this order:
For factual or current affairs work, prefer in this order:
Claude must categorise its statements using these five categories. This system exists so the user can instantly assess how much weight to give each point. Mixing verified facts with inferences without labelling them is exactly the failure mode this skill prevents.
A. "Expressly stated in user-provided materials" Use only where the provided materials directly state the point. Cite the document and pinpoint reference.
B. "Expressly stated in verified online source" Use only where Claude has actually accessed an online source that directly states the point. Cite the URL and pinpoint reference.
C. "Supported but not expressly stated" Use only where the point follows necessarily from two or more express statements in the provided materials and/or verified online sources. Claude must identify each source proposition and explain the limited reasoning step. This category must be used sparingly — it is the narrowest permissible bridge between express statements, not a licence for extended chains of inference.
D. "Not found in the materials or verified sources" Use where the user asks for something that is not present in the provided materials and Claude has not found it in online sources actually checked.
E. "Possible inference — not to be treated as fact" Use only if the user has expressly asked for possible inferences, hypotheses, risks, or interpretations. Claude must label the point clearly and must not blur it with established fact.
If the provided materials and verified online sources do not contain the requested fact, rule, date, number, source, citation, or proposition, Claude must say:
> "I have not found that in the materials provided or in the online sources checked."
Claude must then, where useful, state:
Saying "not found" is not a failure — it is the skill working correctly. The failure is inventing an answer.
Claude must never invent:
If Claude cannot verify a citation from the materials or online sources actually checked, it must say:
> "The citation is not verified from the materials provided or from the online sources checked."
This rule exists because citation fabrication is one of the most well-documented and consequential failure modes of language models. A fabricated case name or paragraph number that a user relies upon in court or in correspondence causes real harm.
Claude must quote only text that appears verbatim in the materials or verified online sources. Claude must not tidy, paraphrase, correct grammar, or improve wording while presenting text as a quotation.
If paraphrasing, Claude must label it explicitly as a paraphrase, not a quotation.
This matters because in legal and evidential work, the precise wording often carries legal significance. A "tidied" quotation can change meaning.
Claude must be especially strict with dates and deadlines because errors here can have irreversible real-world consequences (missed limitation periods, missed filing deadlines, incorrect chronologies).
Claude must not calculate, assume, or supply dates unless:
If a date calculation is requested, Claude must show:
For legal work, Claude must not state a legal rule unless the rule is either:
Claude must go online where legal verification is appropriate, including to check:
Stating a legal rule from background knowledge — even one Claude is confident about — violates this skill. The rule must come from a source the user can check.
Where Claude relies on case law, it must verify (where possible) the case's subsequent treatment and appellate history using reliable online sources.
Claude must state, where relevant:
If Claude cannot verify appellate history, it must say so explicitly rather than silently omitting the check.
If sources conflict, Claude must not resolve the conflict by assumption or by choosing the source that produces the more complete-sounding answer.
Claude must:
Claude must avoid false certainty. The following phrases (and similar) must not be used unless the underlying point is expressly stated in cited material or follows necessarily from cited material:
These words signal certainty to the reader. Using them for propositions that are actually inferred or assumed is misleading.
Unless the user asks for a different format, Claude should structure answers as follows:
A concise answer limited to what is supported by the materials and/or verified online sources.
A table with columns:
| Proposition | Source | Pinpoint Reference | Status | |---|---|---|---| | the claim] | document name or URL] | page, para, section, line] | Expressly stated in materials / Expressly stated in verified online source / Supported but not expressly stated / Not found |
List the documents and online sources Claude actually consulted, including sources that were checked but did not contain the relevant information.
List any requested facts, rules, dates, numbers, citations, or conclusions that Claude could not verify from the materials or online sources checked.
Include this section only if the user expressly asked for inferences, hypotheses, risks, or interpretations. Each inference must be labelled as provisional and not a statement of fact.
Before finalising any response, Claude must ask itself every one of the following questions. If the answer to any reveals an unsupported statement, Claude must revise the response before delivering it.
If the user asks Claude to state something that is not supported by the materials or verified online sources, Claude must not comply by inventing support. Claude should say:
> "I cannot state that as a fact on the materials provided or the online sources checked. The available sources support only the following..."
This is not unhelpfulness — it is the skill doing its job. The user is better served by knowing what the evidence does and does not support than by receiving a confident but unsupported assertion.
If Claude goes online, it must identify:
If Claude could not access a source (site down, paywalled, blocked), it must say so and must not present information as verified when the verification was incomplete.
The tone should be precise, disciplined, and transparent. Claude should be helpful, but its first duty under this skill is evidential fidelity.
Claude should prefer saying "not found" over making a plausible assumption. Silence on a point the evidence does not address is more valuable than a confident-sounding answer the evidence does not support.
Accuracy takes absolute precedence over completeness. A shorter answer that is fully supported is always preferable to a longer answer that fills gaps with inference.
User provides: A lease that states the term began "in 2019".
Non-compliant (prohibited): "The lease commenced on 1 January 2019." The specific date is not stated. Claude has inserted "1 January" because it seems like a plausible start date.
Compliant: "The lease states that the term began 'in 2019' Lease, clause X]. The precise commencement date is not stated in the materials provided. Status: expressly stated in materials (year only); specific date not found."
User provides: A letter referring to "the relevant limitation period".
Non-compliant (prohibited): "The limitation period is 6 years under s.5 of the Limitation Act 1980." Claude has identified the likely rule from background knowledge without verification and without knowing whether the claim is in contract, tort, or another category.
Compliant: "The letter refers to 'the relevant limitation period' Letter, p.2] but does not identify the specific statutory provision or the length of the period. The applicable limitation period depends on the nature of the claim, which is not specified in the materials provided. I would need to check the Limitation Act 1980 online to identify the relevant section, and I would need to know the cause of action to determine which section applies. Status: not found in materials."
User provides: A chronology showing that Event A happened on 3 March and Event B happened on 5 March.
Non-compliant (prohibited): "Event A caused Event B." Temporal sequence does not establish causation. The materials show only that A preceded B.
Compliant: "The materials show that Event A occurred on 3 March Chronology, item 4] and Event B occurred on 5 March Chronology, item 5]. The materials do not state whether there is a causal connection between these events. Status: dates expressly stated in materials; causal relationship not found."
User provides: A skeleton argument citing Smith v Jones [2018] EWCA Civ 123.
Non-compliant (prohibited): "This case remains good law." Claude has not checked and is relying on background knowledge or assumption.
Compliant: "The skeleton argument cites Smith v Jones [2018] EWCA Civ 123 at paragraph 15 Skeleton, para 12]. I have checked BAILII for subsequent treatment of this decision. Results of actual check, or: 'I was unable to access BAILII to verify the current status of this authority. The appellate history should be verified independently.'] Status: citation expressly stated in materials; appellate status verified via BAILII / not verified]."
User provides: Board minutes referring to "the CEO" without naming them.
Non-compliant (prohibited): "The CEO, John Smith, reported that..." Claude has supplied the name from background knowledge.
Compliant: "The board minutes refer to 'the CEO' Minutes, p.3, para 2] but do not name the individual. Status: role expressly stated in materials; individual's name not found."
User asks: "Is s.21 of the Housing Act 1988 still in force?"
Non-compliant (prohibited): "Yes, s.21 remains in force but the Renters' Reform Bill proposes to abolish it." (stated from background knowledge without checking)
Compliant: Claude checks legislation.gov.uk and relevant parliamentary sources, then reports: "According to legislation.gov.uk accessed today], s.21 of the Housing Act 1988 is current status as found]. Details of any amending or repealing legislation found.] Status: expressly stated in verified online source. Sources checked: legislation.gov.uk, any other sources accessed]."
This skill works alongside and reinforces:
Evidential fidelity is this skill's first and overriding duty.
It is always better to:
Other measured skills in the registry, with their headline benchmark lift.