Developer quickstart

Ship cited compliance in one afternoon.

X3 API is simple REST + JSON. Authenticate with a key, then call three core endpoints — search the verified 49 CFR, ask a grounded agent, or pull a carrier by USDOT. Every answer is cited.

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1 · Authenticate

Send your key on every request.

Pass your key in the Authorization header as a bearer token. Keys are scoped per project; the free developer tier includes 1,000 calls a month.

Authorization header

curl https://x3api.com/api/search?q=hours+of+service \
  -H "Authorization: Bearer YOUR_API_KEY"

2 · Call an endpoint

Three endpoints do most of the work.

POST https://x3api.com/api/ask — grounded agent answer

{
  "question": "What are the HOS 14-hour rule limits?",
  "domain": "hos"
}
→ 200 OK
{
  "answer": "The 14-hour limit under §395.3(a)(2) ...",
  "citations": ["49 CFR 395.3"],
  "grounded": true
}

GET https://x3api.com/api/search?q=... — verified CFR / corpus search

GET /api/search?q=drug+testing+pool&limit=6
→ 200 OK
{
  "results": [
    { "section": "49 CFR 382.305",
      "title": "Random testing",
      "text": "Every employer shall ..." }
  ]
}

POST https://x3api.com/api/carrier — carrier safety by USDOT

{ "dot": "1000001" }
→ 200 OK
{
  "legal_name": "SAMPLE CARRIER LLC",
  "authority": "Active",
  "safety_rating": "Satisfactory",
  "basics": [ { "name": "Unsafe Driving", "percentile": 42 } ]
}

3 · Handle responses

Predictable status codes.

200 OK

Success. JSON body with the fields shown above.

401 Unauthorized

Missing or invalid key — check your Authorization header.

429 Too Many Requests

Rate limit reached. Back off and retry, or upgrade your plan.

400 / 500

Bad input or a transient server error — retry with backoff.

Decision support, not legal advice. X3 API returns cited, regulation-grounded information from published sources. It is not legal advice and is not affiliated with FMCSA or USDOT. Verify against the current controlling regulation.

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