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A section lookup tells you what one provision says. These four routes answer the questions you ask next, each starting from an actId you already hold. All four are GET, all sit under https://api.vaquill.ai/api/v1/us/statutes, and all refund a call that cannot answer. Each carries a note explaining an empty answer that is not a real zero, so an empty result with note: null is a genuine “nothing here”.

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Changes: what has moved

GET /us/statutes/section/{actId}/changes returns every change our refreshes have observed to one section: when it was added, each time its text was replaced, and whether it has since been removed. 1 credit.
Each event carries changeKind, detectedAt, displayCitation, hasDiff and the corpusType board it was captured on.
These are OBSERVED changes. detectedAt is when our refresh saw the difference, an upper bound on when it took effect, never the effective date itself. For the publisher’s own dates read amendmentHistory on GET /us/statutes/section/{actId}.Coverage is bounded by capture, not by the age of the law. Change capture began long after the corpus did, runs per source, and events are swept at 24 months. An empty changes list means no captured change, not never amended. The coverage field on the response says so in prose. Surface it rather than rendering an empty list as “unchanged”.
A removed as the newest change means the section is gone from the corpus, so section comes back null. That is a successful, charged response rather than a 404: learning that a provision was repealed is the point.

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Cited-by: the reverse index

GET /us/statutes/section/{actId}/cited-by returns the sections whose text cross-references the one you asked about. 2 credits. A section lookup already tells you what a section cites. This is the other direction, and it is the one you cannot get by reading the section: which provisions elsewhere depend on this one. That is the question behind “if this changes, what else is affected”.
Results are one row per citing section, in statutory order, never one row per matching chunk. total is the size of citers on this page, not a corpus-wide count. Scope: USC and CFR. State codes and Federal Register rules carry no section-level cross-reference index, so a section from either returns an empty list with a note and is refunded.
This reads references as the publisher wrote them. A citation the source never recorded in machine-readable form cannot appear here, so treat a result as evidence of a citation rather than proof there are no others.

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Definitions: the terms that govern a section

GET /us/statutes/section/{actId}/definitions returns the defined terms that apply to a section, parsed from its chapter’s definitions section. 4 credits. No parameters. Statutes do not use ordinary English. “Person” routinely includes corporations, “employee” routinely excludes independent contractors, and the section you are reading almost never says so: the definition lives in a separate section elsewhere in the chapter. Reading a provision without it is how a clause gets misread.
Each entry in terms carries the term as the statute writes it, the definition verbatim, and the marker it sits under where the source numbers its definitions. definitionsSection names where the terms came from, so a definition can be quoted and cited to the provision that actually carries it. Scope: strongest on the U.S. Code, where a chapter’s definitions section is conventionally structured and parses reliably. CFR and state codes are best-effort, because publishers format definitions inconsistently. A definitions section we can locate but not parse returns empty with a note and is refunded, with definitionsSection still populated so you can fetch its text from /section/{actId}/body and read it yourself.

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Cross-state: the same rule elsewhere

GET /us/statutes/section/{actId}/cross-state returns provisions in other states that address the same subject as a state statute section. 6 credits. Answering “how does this rule differ across the states we operate in” normally means running the same search 50 times and reconciling by hand, because every state words and numbers its provisions differently. This starts from one section you already have.
At most one provision per state, most similar first, so the response reads as a jurisdiction comparison rather than a relevance list. statesCovered says how many distinct states are represented. Fewer than you asked for means no provision in the remaining states cleared the similarity floor, not that those states are missing from the corpus. Scope: state statute sections. USC, CFR, regulations and court rules return empty with a note, refunded, since a federal section has no state analogue by definition.
similarity is a retrieval score between 0 and 1 describing how closely two provisions read. It is not a legal opinion.A high score means the provisions cover the same ground, never that they impose the same obligation, and the differences are usually the point. Treat this as the shortlist to read, not the answer.

Section Identifiers

Where an actId comes from, and what to do when one misses.

Status & Currency

Whether the section you are analysing is still good law.

Response Fields

Point-in-time text with asOf, and which fields each corpus populates.

Law Change Alerts

Be told about future changes instead of polling a section’s history.
Last modified on September 6, 2026