eCFR API - US Code of Federal Regulations

Base URL: https://www.ecfr.gov

Admin Service

GET /api/admin/v1/agencies.json

Returns all agencies with their CFR references.

Parameters: None

Response fields: name, short_name, display_name, sortable_name, slug, children[], cfr_references[{title, chapter}]

GET /api/admin/v1/corrections.json

Returns all eCFR corrections.

Parameters:

Name	Type	Description
date	string (query)	Restricts to corrections on/before this date AND corrected on/after. Format: YYYY-MM-DD
title	string (query)	Title number: '1', '2', '50', etc
error_corrected_date	string (query)	Only corrections corrected on this date. Format: YYYY-MM-DD

Response fields: ecfr_corrections[{id, cfr_references[], corrective_action, error_corrected, error_occurred, fr_citation, position, display_in_toc, title, year, last_modified}]

GET /api/admin/v1/corrections/title/{title}.json

Returns corrections for a specific title.

Parameters:

Name	Type	Required	Description
title	string (path)	Yes	Title number: '1', '2', '50', etc

Search Service

All search endpoints share these common parameters:

Name	Type	Description
query	string (query)	Search term; searches headings and full text
agency_slugs[]	array[string] (query)	Limit to agencies (get slugs from agencies endpoint)
date	string (query)	Limit to content present on this date (YYYY-MM-DD)
last_modified_after	string (query)	Content modified after this date (YYYY-MM-DD)
last_modified_on_or_after	string (query)	Content modified on or after this date (YYYY-MM-DD)
last_modified_before	string (query)	Content modified before this date (YYYY-MM-DD)
last_modified_on_or_before	string (query)	Content modified on or before this date (YYYY-MM-DD)

GET /api/search/v1/results

Search results with pagination.

Additional parameters:

Name	Type	Description
per_page	integer (query)	Results per page (max 1000)
page	integer (query)	Page number (can't paginate beyond 10,000 total results)
order	string (query)	Order of results
paginate_by	string (query)	'date' groups results by date on same page (requires last_modified_* param)

Response: {results[], meta: {description, current_page, total_count, total_pages, max_score, min_date, max_date}}

GET /api/search/v1/count

Returns count of matching results.

GET /api/search/v1/summary

Returns search summary details.

GET /api/search/v1/counts/daily

Returns result counts grouped by date.

GET /api/search/v1/counts/titles

Returns result counts grouped by CFR title.

GET /api/search/v1/counts/hierarchy

Returns result counts grouped by hierarchy level.

GET /api/search/v1/suggestions

Returns search suggestions/autocomplete.

Versioner Service

GET /api/versioner/v1/titles.json

Summary information about each title.

Parameters: None

Response: {titles[{number, name, latest_amended_on, latest_issue_date, up_to_date_as_of, reserved, processing_in_progress?}], meta: {date, import_in_progress}}

GET /api/versioner/v1/structure/{date}/title-{title}.json

Complete structure of a title as JSON (no content, just hierarchy).

Parameters:

Name	Type	Required	Description
date	string (path)	Yes	YYYY-MM-DD (use 'current' for latest)
title	string (path)	Yes	Title number: '1', '2', '50', etc

Response: Nested structure with {type, label, label_level, label_description, identifier, reserved?, children[], section_range?}

GET /api/versioner/v1/full/{date}/title-{title}.xml

Source XML for a title or subset. Returns downloadable XML for full titles, processed XML for subsets.

Parameters:

Name	Type	Required	Description
date	string (path)	Yes	YYYY-MM-DD
title	string (path)	Yes	Title number: '1', '2', '50', etc
subtitle	string (query)	No	Uppercase letter: 'A', 'B', 'C'
chapter	string (query)	No	Roman numerals or digits: 'I', 'X', '1'
subchapter	string (query)	No	Requires chapter. Uppercase letters: 'A', 'B', 'I'
part	string (query)	No	Part identifier
subpart	string (query)	No	Requires part. Generally uppercase letter: 'A', 'B', 'C'
section	string (query)	No	Requires part. Format: '121.1', '13.4', '1.9'
appendix	string (query)	No	Requires subtitle, chapter, or part. Formats: 'A', 'III', 'App. A'

GET /api/versioner/v1/ancestry/{date}/title-{title}.json

Returns complete hierarchy path from leaf node to title root.

Parameters: Same as full XML endpoint above.

Response: Array of ancestors from title down to requested node, each with {type, label, label_level, label_description, identifier, reserved?, section_range?}

GET /api/versioner/v1/versions/title-{title}.json

Returns all sections and appendices in a title with version history.

Parameters:

Name	Type	Required	Description
title	string (path)	Yes	Title number: '1', '2', '50', etc
issue_date[on]	string (query)	No	Content added on this issue date
issue_date[lte]	string (query)	No	Content added on or before this date
issue_date[gte]	string (query)	No	Content added on or after this date
subtitle	string (query)	No	Uppercase letter: 'A', 'B', 'C'
chapter	string (query)	No	Roman numerals or digits: 'I', 'X', '1'
subchapter	string (query)	No	Requires chapter.
part	string (query)	No	Part identifier
subpart	string (query)	No	Requires part.
section	string (query)	No	Requires part.
appendix	string (query)	No	Requires subtitle, chapter, or part.

Response: {content_versions[{date, amendment_date, issue_date, identifier, name, part, substantive, removed, subpart, title, type}], meta: {title, result_count, issue_date, latest_amendment_date, latest_issue_date}}

Error codes: 400 (bad request with message), 503 (title being processed, check Retry-After header)

CFR Title Reference

#	Subject
1	General Provisions
2	Federal Financial Assistance
3	The President
7	Agriculture
10	Energy
12	Banks and Banking
14	Aeronautics and Space
17	Commodity and Securities Exchanges
20	Employees' Benefits
21	Food and Drugs
26	Internal Revenue
29	Labor
40	Protection of Environment
42	Public Health
45	Public Welfare
47	Telecommunication
49	Transportation
50	Wildlife and Fisheries

Hierarchy Dependency Rules

•subchapter requires chapter
•subpart requires part
•section requires part
•appendix requires subtitle, chapter, or part