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API Overview

The LexBuild Data API provides programmatic access to over one million structured U.S. legal documents. You can retrieve individual sections, list and filter collections, search across sources, and browse hierarchical structures — all through a standard REST interface.

Base URL: https://lexbuild.dev/api

All endpoints are prefixed with /api/. There is no version prefix in the URL — new sources and fields are added without breaking existing responses.

Supported Sources

The API serves three sources of U.S. federal law:

SourcePath PrefixDescription
U.S. Code (USC)/api/usc/General and permanent federal statutes organized into 54 titles
eCFR/api/ecfr/Continuously updated CFR content organized into 50 titles
Federal Register (FR)/api/fr/Daily journal of the U.S. government: rules, proposed rules, notices, and presidential documents

The API uses ecfr in route prefixes and source filters because the current regulatory corpus comes from the Electronic Code of Federal Regulations. Canonical document identifiers still use the /us/cfr/... namespace because the identifier scheme is keyed to the content type rather than the transport source.

Key Features

  • Content negotiation — Get responses as JSON (default), raw Markdown with YAML frontmatter, or stripped plaintext. Use the Accept header or ?format= query parameter.
  • Pagination — Offset-based pagination with configurable limits, totals, and a next link for easy traversal. Document collection endpoints also support cursor pagination for deep result sets.
  • Filtering and sorting — Source-specific filters (title number, agency, document type, date ranges) and multi-field sorting.
  • Field selection — Request only metadata, only the body, or specific fields to reduce response size.
  • Full-text search — Cross-source search with faceted filtering, highlighting, and relevance ranking.
  • ETag caching — Every document response includes an ETag header. Send If-None-Match to get a 304 Not Modified when the content has not changed.
  • Rate limiting — Tiered rate limits with transparent X-RateLimit-* headers on every response.

Quick Example

Fetch U.S. Code Title 1, Section 1 as JSON:

curl https://lexbuild.dev/api/usc/documents/t1%2Fs1
{
  "data": {
    "id": "us-usc-t1-s1",
    "identifier": "/us/usc/t1/s1",
    "source": "usc",
    "metadata": {
      "identifier": "/us/usc/t1/s1",
      "source": "usc",
      "display_title": "1 U.S.C. 1 - Words denoting number, gender, and so forth",
      "title_number": 1,
      "title_name": "General Provisions",
      "section_number": "1",
      "section_name": "Words denoting number, gender, and so forth",
      "chapter_number": "1",
      "chapter_name": "Rules of Construction",
      "legal_status": "law",
      "positive_law": true,
      "status": "in_force"
    },
    "body": "In determining the meaning of any Act of Congress..."
  },
  "meta": {
    "api_version": "v1",
    "format_version": "1.0",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

When you use cursor pagination on document collection endpoints, pagination.total becomes null because the API skips the expensive count query.

Interactive Documentation

The API includes a built-in interactive reference powered by Scalar. You can browse all endpoints, see request/response schemas, and test requests directly in your browser:

The OpenAPI 3.1 spec can be imported into tools like Postman, Insomnia, or any OpenAPI-compatible client.

Response Envelope

All JSON responses follow a consistent envelope structure:

{
  "data": { },
  "meta": {
    "api_version": "v1",
    "format_version": "1.0",
    "timestamp": "2026-04-04T12:00:00.000Z"
  }
}

Collection endpoints add a pagination object:

{
  "data": [ ],
  "meta": { },
  "pagination": {
    "total": 1542,
    "limit": 20,
    "offset": 0,
    "has_more": true,
    "next": "/api/usc/documents?offset=20&limit=20"
  }
}

Next Steps