Hierarchy Endpoints

Hierarchy endpoints let you browse the organizational structure of each source. USC and eCFR are organized by title and chapter in the hierarchy endpoints. The Federal Register is organized by year and month.

U.S. Code Titles

List All USC Titles

GET /api/usc/titles

Returns all 54 USC titles with document counts and chapter counts.

curl https://lexbuild.dev/api/usc/titles

{
  "data": [
    {
      "title_number": 1,
      "title_name": "General Provisions",
      "document_count": 10,
      "chapter_count": 3,
      "positive_law": true,
      "url": "/api/usc/titles/1"
    },
    {
      "title_number": 2,
      "title_name": "The Congress",
      "document_count": 1437,
      "chapter_count": 65,
      "positive_law": false,
      "url": "/api/usc/titles/2"
    }
  ],
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

Get USC Title Detail

GET /api/usc/titles/{number}

Returns metadata for a single title along with its chapter listing.

curl https://lexbuild.dev/api/usc/titles/17

{
  "data": {
    "title_number": 17,
    "title_name": "Copyrights",
    "document_count": 463,
    "positive_law": true,
    "chapters": [
      {
        "chapter_number": "1",
        "chapter_name": "Subject Matter and Scope of Copyright",
        "document_count": 26
      },
      {
        "chapter_number": "2",
        "chapter_name": "Copyright Ownership and Transfer",
        "document_count": 12
      }
    ]
  },
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

If the title does not exist, the API returns a 404 error.

eCFR Titles

List All eCFR Titles

GET /api/ecfr/titles

Returns all 50 eCFR titles with document and chapter counts. The response shape is identical to the USC title listing.

curl https://lexbuild.dev/api/ecfr/titles

{
  "data": [
    {
      "title_number": 1,
      "title_name": "General Provisions",
      "document_count": 134,
      "chapter_count": 4,
      "positive_law": false,
      "url": "/api/ecfr/titles/1"
    }
  ],
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

Get eCFR Title Detail

GET /api/ecfr/titles/{number}

Returns an eCFR title with its chapter breakdown.

curl https://lexbuild.dev/api/ecfr/titles/40

{
  "data": {
    "title_number": 40,
    "title_name": "Protection of Environment",
    "document_count": 8432,
    "positive_law": false,
    "chapters": [
      {
        "chapter_number": "I",
        "chapter_name": "Environmental Protection Agency",
        "document_count": 7891
      }
    ]
  },
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

Federal Register Years

The Federal Register uses a date-based hierarchy instead of titles.

List All Years

GET /api/fr/years

Returns all publication years with document counts, sorted in reverse chronological order.

curl https://lexbuild.dev/api/fr/years

{
  "data": [
    {
      "year": 2026,
      "document_count": 8234,
      "url": "/api/fr/years/2026"
    },
    {
      "year": 2025,
      "document_count": 28451,
      "url": "/api/fr/years/2025"
    },
    {
      "year": 2024,
      "document_count": 29102,
      "url": "/api/fr/years/2024"
    }
  ],
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

Get Year Detail

GET /api/fr/years/{year}

Returns month-by-month breakdown for a given year.

curl https://lexbuild.dev/api/fr/years/2026

{
  "data": {
    "year": 2026,
    "document_count": 8234,
    "months": [
      {
        "month": 1,
        "document_count": 2891,
        "url": "/api/fr/years/2026/01"
      },
      {
        "month": 2,
        "document_count": 2654,
        "url": "/api/fr/years/2026/02"
      },
      {
        "month": 3,
        "document_count": 2689,
        "url": "/api/fr/years/2026/03"
      }
    ]
  },
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

Get Month Documents

GET /api/fr/years/{year}/{month}

Returns a paginated list of documents published in a specific month. The month parameter accepts one or two digits (for example, 3 or 03 for March).

Query parameters:

curl https://lexbuild.dev/api/fr/years/2026/03

{
  "data": {
    "year": 2026,
    "month": 3,
    "document_count": 2689,
    "documents": [
      {
        "id": "fr-2026-05001",
        "identifier": "/us/fr/2026-05001",
        "document_number": "2026-05001",
        "display_title": "Air Quality Standards for Ozone",
        "document_type": "rule",
        "publication_date": "2026-03-01",
        "agency": "Environmental Protection Agency"
      },
      {
        "id": "fr-2026-05002",
        "identifier": "/us/fr/2026-05002",
        "document_number": "2026-05002",
        "display_title": "Request for Comments on Proposed Banking Regulations",
        "document_type": "notice",
        "publication_date": "2026-03-01",
        "agency": "Federal Deposit Insurance Corporation"
      }
    ]
  },
  "meta": {
    "api_version": "v1",
    "timestamp": "2026-04-04T12:00:00.000Z"
  },
  "pagination": {
    "total": 2689,
    "limit": 100,
    "offset": 0,
    "has_more": true,
    "next": "/api/fr/years/2026/03?limit=100&offset=100"
  }
}

If no documents exist for the requested year or month, the API returns a 404 error.

Combining Hierarchy and Document Endpoints

The hierarchy endpoints are useful for discovery and navigation. Once you know the structure, use the document endpoints to retrieve content:

# 1. Browse USC titles
curl https://lexbuild.dev/api/usc/titles

# 2. See chapters in Title 42
curl https://lexbuild.dev/api/usc/titles/42

# 3. List sections in that title
curl "https://lexbuild.dev/api/usc/documents?title_number=42&limit=50"

# 4. Retrieve a specific section
curl https://lexbuild.dev/api/usc/documents/t42%2Fs1983