Search and retrieve docket documents from the Regulations.gov v4 API and submit a public comment

Steps

1. Obtain a free API key from api.data.gov; the key is passed in the X-Api-Key HTTP request header for all Regulations.gov v4 API calls.
2. Search for dockets using GET https://api.regulations.gov/v4/dockets?filter[searchTerm]={keyword}&api_key=YOUR_API_KEY; parse the docketId from results for subsequent calls.
3. Retrieve documents in a docket via GET https://api.regulations.gov/v4/documents?filter[docketId]={docketId}&api_key=YOUR_API_KEY; filter by documentType (Proposed Rule, Rule, Notice, Supporting Material) using filter[documentType].
4. To submit a public comment, POST to https://api.regulations.gov/v4/comments with a JSON body including commentOnDocumentId, comment text, and submitterType; file attachments require a prior call to retrieve a submission key.
5. For attachments, POST to the fileUpload endpoint to get a presigned URL, upload the file binary, then include the returned fileUploadId in the comment POST body.
6. The comment submission POST endpoint is rate-limited to 500 requests per hour; standard GET requests allow up to 1,000 per hour. Return status 429 with a Retry-After header signals rate exhaustion.