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corpusType chooses which body of law a search runs against. It is the single most important filter in the API: it decides whether you get a statute, a regulation, a court rule, agency guidance or a decided case.
Pass one token or a list. This page is the query vocabulary: what each token means and how to scope it. For how much data sits behind each one and what is deliberately excluded, see API Coverage.

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Scoping rules

1

A federal token needs only corpusType

2

A state token needs corpusType and state

Omit state on a state-scoped token and the search spans every jurisdiction that has that corpus ingested, which is rarely what you want and always costs the same.
state also accepts a list, so one call can cover several jurisdictions.
3

Narrow further with source, where a token folds in several bodies

titleNumber is only valid alongside corpusType USC or CFR. Sending it with any other token returns a 422.

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The 22 tokens

Sizes are distinct sections, measured 2026-10-13 from GET /us/statutes/coverage. Call GET /us/statutes/coverage for a live figure and for which tokens have data in which jurisdiction. The OpenAPI enum also accepts USC_ANNUAL, GPO’s retired annual edition of the US Code, which is kept only so a past date can be answered from a printed edition. It is not a token to search.

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Federal-scoped

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State-scoped

Each of these requires state, or spans every jurisdiction holding that corpus. State session laws have no corpusType. They are served by /us/session-laws, not /us/statutes. SESSION_LAW is the federal Statutes at Large only.

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STATE_REGISTER in particular

A state’s official register prints each proposed, adopted or emergency rule as a notice on a date. STATE_REGISTER holds those notices, one document per printed item, cited by register volume and page (36 Pa. Bull. 510).
A register notice is not the law. The codified rule under REGULATION is the operative text, and a register page often prints a rule that was later withdrawn, amended or never adopted. Every item is served with goodLawStatus: "unknown", year is the year of the issue it was printed in, and it is never given the priority that binding law gets in search ranking. Name the token when you want register notices, and do not read one as the rule in force.
Cite a register item by its register citation; see Register citations. The states loaded are listed on State and territory coverage.

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STATE_AG_OPINION in particular

A formal written opinion in which a state’s chief legal officer construes that state’s own statutes, constitution and regulations for a state officer, legislator or local government who asked.
An AG opinion is persuasive authority, not binding law. Officials follow them in practice, and an AG opinion is very often the only interpretive authority that exists for a provision no court has reached — which is the reason to hold the corpus at all. But it does not bind a court, and it must not be read as the rule.Every section in this corpus is served with goodLawStatus: "unknown". That is by construction, not an omission: only three of the 52 jurisdictions publish any supersession signal at all, so we will not certify an opinion as still standing. See Status and currency.
Where a jurisdiction runs more than one series, the series field carries the publisher’s own label, so you can filter Washington’s formal AGO apart from its AGLO letter opinions, or Georgia’s Official from its Unofficial opinions. The series is also part of the actId, which is what makes the field trustworthy rather than derived from a title.

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Choosing between tokens that look alike

Five pairs are routinely confused, and picking the wrong one returns a confident answer to a different question. For asking any corpus what it said on a past date, see Point-in-time law. SESSION_LAW and STATUTE_COMPILATION both carry goodLawStatus: "unknown" by design: they are historical records, not statements of current law.

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Filtering to one named source

AGENCY_GUIDANCE, AGENCY_ADJUDICATION, FEDERAL_RULES, CFR, US_TAX_TREATY and STATE_AGENCY_GUIDANCE each fold several independently filterable bodies into one token. Every result carries a source field naming which one it came from; pass that value back as the source filter to scope to it.
source accepts a single value or a list, so source: ["frcp", "sct"] searches both in one call. An unrecognized value is rejected with 422 and the error names every valid code, so the API itself is the authoritative list.
The far and dfars sources split existing Title 48 data by chapter. They are not a separate ingest and do not add sections to the CFR total.

API Coverage

How much sits behind each token, and what each corpus deliberately excludes.

Jurisdictions and state codes

The 56 jurisdictions and how to discover live coverage.
Last modified on October 13, 2026