Retrieve public comments from the Regulations.gov API

Steps

1. Register for a Regulations.gov API key at api.regulations.gov; the API key is required for all calls and must be included as the api_key query parameter.
2. Identify the docket or document you are interested in by querying https://api.regulations.gov/v4/documents?filter[agencyId]={AGENCY}&filter[documentType]=Proposed%20Rule&api_key=your_api_key to find documents open for comment.
3. Retrieve comments for a specific document using the objectId returned from the document response: GET https://api.regulations.gov/v4/comments?filter[commentOnId]={objectId}&api_key=your_api_key.
4. Paginate through results: the default page size is 25, the maximum is 250 (set with page[size]=250), and the API caps total results at 5,000 per query; for dockets with more than 5,000 comments use date range filters (filter[postedDate][ge] and filter[postedDate][le]) to break up the query.
5. To retrieve the full text and attachments for a specific comment, call GET https://api.regulations.gov/v4/comments/{commentId}?include=attachments&api_key=your_api_key; attachments are returned as download URLs.
6. Note that date filter formats differ: postedDate filters use YYYY-MM-DD but lastModifiedDate filters use YYYY-MM-DD HH24:MI:SS in Eastern time.