M
API Matrix

Lob.com API

Data Validation / API Key Intermediate HTTPS
Varies by plan (check documentation)
82 Score
Grade A
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Overview

Lob.com provides a US Address Verification API that validates, standardizes, and geocodes US mailing addresses using USPS data, ensuring mail deliverability and cleaning up address databases. It also supports international address verification, address autocomplete, and physical mail sending (postcards, letters, checks) via API. The free test mode allows unlimited verifications against a sandbox environment.

💡

Beginner Tip

Create an account at lob.com and use the test API key (prefixed with `test_`) for free sandbox verification. The verification endpoint is `https://api.lob.com/v1/us_verifications`. Authentication uses HTTP Basic Auth — set the API key as the username with an empty password. Test keys return standardized results but do not charge credits.

Available Data

Use case: Integrate us address verification data into web and mobile applications
Lob.com data via REST API
JSON-formatted response data
Requires API key authentication

Example Response

JSON Response 
{
  "status": "success",
  "data": {
    "result": "Data from Lob.com",
    "description": "US Address Verification",
    "timestamp": "2025-01-15T10:00:00Z"
  }
}

Field Reference

deliverability USPS deliverability status: `deliverable`, `deliverable_unnecessary_unit`, `deliverable_incorrect_unit`, `deliverable_missing_unit`, or `undeliverable`.
primary_line The standardized first line of the address (street number and name).
last_line The standardized city, state, and ZIP+4 code on the last line.
components Parsed address components including street number, street name, city, state, zip code, and zip+4.
urbanization Urbanization code used for Puerto Rico addresses; empty for continental US addresses.

Implementation Example 

const url = "https://lob.com/";
// Replace headers or query params with the values required by this API.
const response = await fetch(url, {
  headers: {
  "X-API-Key": "YOUR_API_KEY"
  }
});
if (!response.ok) throw new Error(`Request failed: ${response.status}`);
const data = await response.json();
console.log(data);

What Can You Build?

Note: These code examples are AI-generated and unverified. Always refer to the official API documentation for accurate usage.

Common Errors & Troubleshooting

401 Unauthorized Incorrect Basic Auth format. Lob requires the API key as the HTTP Basic username, not a Bearer token.
✓ Use `curl -u 'YOUR_API_KEY:' https://api.lob.com/v1/us_verifications` — note the colon after the key indicating an empty password.
deliverability: undeliverable for a real address Address input is malformed, using abbreviations that USPS cannot parse, or missing a zip code.
✓ Provide `primary_line`, `city`, `state`, and `zip_code` as separate fields. Avoid concatenated strings. Use the autocomplete endpoint to pre-clean inputs.
Exceeded free tier verifications in live mode Live API keys consume verification credits which are not free.
✓ Use the test key (`test_*`) for development and testing — it runs all verifications against a sandbox at no cost.

Matrix Score Breakdown

🌐 Reachability 30/30
⚡ Speed 15/20
🔒 Security 15/15
🛠 Developer XP 12/20
✓ Reliability 10/15

Partially tested on Apr 5, 2026

Technical Specifications

Auth API Key
HTTPS REQUIRED
CORS UNKNOWN
Category Data Validation
Difficulty Intermediate
Verified: 2026-04-07

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