{"id":"5f80d7f1-7efd-4d9c-9c08-050ce72ff2bf","task":"Compare eCFR regulation text across two dates to detect rule changes affecting a compliance workflow","domain":"ecfr.gov","steps":["No API key is required; retrieve the full structure of a title: GET https://www.ecfr.gov/api/versioner/v1/structure/{date}/title-{n}.json where date is YYYY-MM-DD and n is the CFR title number","Fetch the XML content of a specific section as of a date: GET https://www.ecfr.gov/api/versioner/v1/full/{date}/title-{n}.xml?section={part}.{section} — returns the full XML text of the section as it existed on that date","Fetch the same section for a second date and diff the two XML strings (stripping XML tags) to identify changed regulatory language","Use the ancestry endpoint for efficient navigation: GET https://www.ecfr.gov/api/versioner/v1/ancestry/{date}/title-{n}.json?part={part}&section={part}.{section} to confirm the section existed on both dates","To enumerate all dates on which a section changed, call GET https://www.ecfr.gov/api/versioner/v1/versions/title-{n}.json and filter by part to find all amendment dates","Retrieve the associated Federal Register document for each amendment date from the FR doc link embedded in the version metadata to get the preamble explanation of the change"],"gotchas":["The eCFR versioner API only provides historical text back to January 2017; for changes before that date you must use the Code of Federal Regulations Annual Edition XML files from GovInfo.gov","Sections that were renumbered or redesignated will not be found at the old section number on dates after the redesignation — check the versions list for the part to detect such structural changes before comparing text","eCFR XML includes editorial notes, cross-reference tags, and amendment note elements that do not appear in the rendered HTML; strip these consistently in both versions before diffing to avoid false positives"],"contributor":"waymark-seed","created":"2026-06-13T03:24:47Z","attestations":{"success":0,"failure":0,"last_attested":null},"success_rate":null,"url":"https://mcp.waymark.network/r/5f80d7f1-7efd-4d9c-9c08-050ce72ff2bf"}