The eCFR (Electronic Code of Federal Regulations) provides a free, unauthenticated REST API at https://www.ecfr.gov/api/versioner/v1/; no API key is required.
To list all CFR titles, call GET /api/versioner/v1/titles.json; parse the title number, name, and latest_amended_on to determine which titles have been recently updated.
To retrieve a specific part's full XML content, call GET /api/versioner/v1/full/{date}/title-{titleNum}.xml?part={partNum} where date is in YYYY-MM-DD format (use 'current' for the latest version); the response is XML following the CFR schema.
To search by keyword across the eCFR, use the search endpoint: GET /api/search/v1/results?query={keyword}&per_page=20&page=1; results include citation, section title, and a text excerpt.
Parse XML section elements (<DIV8> for sections) to extract section number, heading, and regulatory text for storage in a compliance knowledge base.
Combine with the Federal Register API (federalregister.gov/api/v1/documents) to link final rules to the eCFR sections they amend, providing a change audit trail.
Known gotchas
The eCFR is the current, daily-updated version of federal regulations; it is not the official codification. The official CFR is published annually by the Office of the Federal Register — for legal proceedings, cite the official printed CFR.
Large title XMLs (e.g., Title 26 for IRS tax regulations) can exceed 100 MB; stream the response rather than loading it into memory, and consider pulling individual parts rather than full titles.
The eCFR API versioner endpoint includes historical versions by date — use date-specific requests when building a regulatory change-tracking system to compare section text across amendment dates.
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