M
API Matrix

US Autocomplete API

Data Validation / API Key Intermediate HTTPS CORS
Varies by plan (check documentation)
47 Score
Grade D
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Overview

Smarty's US Autocomplete Pro API provides real-time US address suggestions as users type, returning up to 10 valid USPS-deliverable address candidates per query to reduce data entry errors and speed up checkout flows. It uses USPS data to ensure every suggested address is a real, deliverable location rather than a guess. A free plan is available with a limited number of lookups per month.

💡

Beginner Tip

Sign up at smarty.com for a free API key (embedded key). The endpoint is `https://us-autocomplete-pro.api.smarty.com/lookup?key=YOUR_KEY&search=123+Main`. Pass the partial address as the `search` parameter. Each keystroke query counts as one lookup — debounce your input handler to avoid burning through your free quota quickly.

Available Data

vehicle make and model
year and specifications
fuel economy
VIN decode data

Example Response

JSON Response 
{
  "make": "Toyota",
  "model": "Camry",
  "year": 2025,
  "engine": "2.5L 4-cylinder",
  "fuel_economy": {
    "city_mpg": 28,
    "highway_mpg": 39
  },
  "msrp": 28400
}

Field Reference

suggestions Array of address suggestion objects matching the partial input.
suggestions[].street_line The suggested street address line (e.g., `123 Main St`).
suggestions[].secondary Secondary address info such as apartment or suite number, if applicable.
suggestions[].city City name for the suggested address.
suggestions[].state Two-letter US state abbreviation.
suggestions[].zipcode Five-digit ZIP code for the suggested address.

Implementation Example 

const url = "https://www.smarty.com/docs/cloud/us-autocomplete-pro-api";
// 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 or bad credentials Using a server-side secret key instead of an embedded/browser key, or the key has not been assigned the Autocomplete Pro product.
✓ In your Smarty dashboard, generate an `Embedded Key` specifically for autocomplete. Server-side keys are restricted and require IP whitelisting.
Empty suggestions array for valid addresses Query string is too short (less than 3 characters) or contains only numbers without a street name.
✓ Wait until the user has typed at least 3 characters including part of a street name before making the API call.
Exceeded lookup quota Burning through free lookups by calling the API on every keypress.
✓ Debounce input events to fire only after 300ms of inactivity, and set a minimum query length of 3 characters. Cache repeated identical queries.

Matrix Score Breakdown

🌐 Reachability 0/30
⚡ Speed 15/20
🔒 Security 15/15
🛠 Developer XP 17/20
✓ Reliability 0/15

Partially tested on Apr 5, 2026

Technical Specifications

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

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