LRN Lookup API Reference

Overview

All endpoints are served over HTTPS. Responses are JSON. Request and response bodies use UTF-8 encoding. Phone numbers must be in E.164 format (e.g., +12125551234).

Authentication

All API requests require an API key passed in the Authorization header as a Bearer token. API keys are issued instantly upon account registration.

Authorization: Bearer YOUR_API_KEY

Endpoint: LRN Lookup

Returns portability and routing information for a single U.S. telephone number.

Path Parameter

Example Request

GET /lrn/+12125551234

Successful Response (200)

{
  "phone_number": "+12125551234",
  "lrn": "2125550000",
  "ported": true,
  "ocn": "1234",
  "carrier_name": "Example Carrier Inc.",
  "rate_center": "NEW YORK",
  "state": "NY",
  "last_updated": "2026-01-12T15:22:31Z"
}

Response Schema

Error Responses

{ "error": "Invalid phone number format. Use E.164." }

{ "error": "Unauthorized" }

{ "error": "Number not found" }

{ "error": "Rate limit exceeded" }

Bulk Lookup Endpoint

Submit up to 10,000 numbers per request. Returns an array of portability results in the same order as the input. For larger batches (up to 1,000,000 numbers), use the async enrichment jobs API.

Request Body

{
  "numbers": [
    "+12125551234",
    "+13105559876"
  ]
}

Response is an array of the same objects as the single lookup endpoint, one per input number. Numbers not found are omitted (no null entries).

Rate Limits

Distributed infrastructure enables horizontal scaling for high-volume environments. Contact us for throughput above 50 req/sec.

Latency Targets

Actual latency varies by geographic proximity to the nearest U.S. replication endpoint. See Distributed LRN Infrastructure for endpoint topology.

Code Examples

curl

curl -H "Authorization: Bearer YOUR_API_KEY" \
  https://api.sipsmart.io/v1/lrn/+12125551234

Node.js

import fetch from "node-fetch";

const response = await fetch(
  "https://api.sipsmart.io/v1/lrn/+12125551234",
  {
    headers: {
      Authorization: "Bearer YOUR_API_KEY"
    }
  }
);

const data = await response.json();
console.log(data);

Python

import requests

headers = {
    "Authorization": "Bearer YOUR_API_KEY"
}

response = requests.get(
    "https://api.sipsmart.io/v1/lrn/+12125551234",
    headers=headers
)

print(response.json())

Data Freshness

Portability data is synchronized continuously using incremental NPAC update streams. Replication nodes are updated automatically to maintain near-real-time portability accuracy. The last_updated field in each response reflects the most recent NPAC event timestamp for that number.

High-Volume Integration Guidance

For predictive dialers and SIP routing platforms:

• 1Normalize numbers to E.164 before querying.
• 2Cache results for short-term re-use where appropriate (check last_updated to validate freshness).
• 3Monitor p95 latency via your observability stack.
• 4Use the bulk endpoint for batch validation workflows.
• 5Use the async jobs endpoint for large enrichment batches (100k–1M numbers).

Infrastructure Model

SIPSmart operates distributed U.S. replication endpoints to reduce round-trip time and eliminate single-region bottlenecks. The 251M-row LRN database uses a covering index — queries read only the index, not full row data, enabling throughput of ~1M lookups/sec per node.

Frequently Asked Questions