Search the Federal Register — the daily journal of US proposed rules, final rules, notices, and presidential documents (1994–present) — filtering by full-text query, document type, agency slug, publication date range, affected CFR title and part, printed docket number, RIN, EO 12866 significance, effective date range, and for presidential documents the executive order number, subtype, president, and signing date range, all combined. A page cite from a CFR source note ("89 FR 49102", with its date) resolves to the documents printed on that page. The primary discovery entry point: results carry the document number (open with regulations_get_document), its citation and page range, each issuing agency with its filterable slug, printed docket numbers, Regulations.gov docket and document IDs, comment count and comment URL, whether the comment period is open, RINs, significance, presidential-document identifiers, and affected CFR parts that chain into the comment and codified-text tools. A query ranks by relevance unless order says otherwise; filter-only browsing lists newest first. The Federal Register caps navigation at 50 pages and the match count at 10,000; when a result set is larger, narrow with published_after/published_before rather than paging deeper.
Fetch one Federal Register document by its FR document number — full metadata (title, type, agencies, abstract, action, effective/comment dates, RINs, EO 12866 significance, and for a presidential document its subtype, number, signing date, and president) plus the cross-source handles that make this a workflow server. The output carries the Regulations.gov docket ID (chain into regulations_get_docket or regulations_find_comments), the docket numbers the Federal Register prints (chain back into regulations_search_rules as docket_id), the comment count and comment URL, and the affected CFR parts (chain into regulations_get_cfr_section). Set include_full_text only when the rule body itself is needed: it returns the plain-text body as a window of up to 64,000 characters (max_chars raises it to 200,000), with the body's total length and, when text remains, the offset to resume from. Short documents return whole; major final rules run past a million characters, so page through with offset rather than reading them in one call.
Explore the codified Code of Federal Regulations via eCFR in three modes. "structure" lists all 50 titles; with a title, that title's top-level divisions (its chapters, or subtitles); and with a title and part, every section and appendix in the part, flattened and paged, each naming the subpart and subject group it sits under — the way to enumerate a part's sections without reading its text. "search" runs a full-text query across the codified CFR and returns matching sections with their hierarchy path and a snippet, one result per section, paged. "versions" lists the dates a part's or one section's text changed, oldest first per section, paged, with the latest amendment date; with changed_since, what changed across a title. Every mode accepts title and part to narrow the scope, and all three feed regulations_get_cfr_section — a version row's `date` reads that version. Every search result reports which corpus answered it — the synced local mirror or the live eCFR index — and what that corpus covers, in `source` and `sourceScope`.
Read the codified text at a CFR location via eCFR — current or as of a past date. Answers "what does 40 CFR 50.1 say today?" and "...as of 2019-01-01?". Three locations: title + part + section for one section; title + part alone for the whole part, with its Authority and Source notes, an index of its sections, and the names of its appendices; title + appendix for one appendix, passing the identifier exactly as regulations_browse_cfr emits it. A section can be written as people cite it — "61", "§ 141.61", "141.61(c)", or the full cite "40 CFR 141.61" in part 141 all read 40 CFR 141.61 — and a part as "Part 141"; the response names the identifier it read. Text comes back as a window of up to 64,000 characters (max_chars raises it to 200,000) with the total length and, when text remains, the offset to resume from; whole parts run to millions of characters, so page with offset or read a single section. eCFR retains historical versions from 2017 through the title's up-to-date date; a date outside that window is rejected with the window named. Current single-section reads are served from a synced local mirror when it holds the title's latest eCFR issue; the source is reported.
Pull a rulemaking docket from Regulations.gov by docket ID (e.g. "EPA-HQ-OAR-2025-0194") — the docket's metadata (title, agency, RIN, abstract) and the documents filed in it (NPRM, final rule, supporting materials) — or read one document by document_id for its file download URLs and attachments, which a docket listing does not carry. Provide exactly one of docket_id / document_id. The docket is the folder holding a rule's whole paper trail; each returned document's objectId feeds regulations_find_comments. A docket often contains hundreds of supporting materials — find one with search_term, or filter document_types to "Proposed Rule"/"Rule" for the rule documents themselves. Requires REGULATIONS_GOV_API_KEY (free at https://api.data.gov/signup/); the Federal Register and eCFR tools work without it.