The USPS API is an address validation API provided by the United States Postal Service. It provides developers of web-based applications access to the complete USPS database of postal address information for the United States.

(You can access a demo of the USPS address validation api data for free.)

In reality, the USPS offers multiple APIs. They are as follows:

  • Address Verification API
  • ZIPCode API
  • Address Standardization API

Each of these APIs perform specific functions such as address validation, address normalization, ZIP+4 appending, and more.

USPS Address Verification API

If you're just looking to use the USPS API itself, here is a list of resources:

USPS Web Tools:


NOTE: A faster and easier way to access the same data of the USPS database is to use any of the SmartyStreets Address Validation APIs instead.

Each of the SmartyStreets APIs:

  • contains all of the data of the USPS database
  • is fully documented
  • has live support
  • is famously easy to integrate.
  • has 100% uptime


Why would we bring up the USPS API status? Because even though the US Postal service database is the official repository of address info for the United States, their API is well-known for its lack of consistent uptime.

It may be free, but it comes at a price: reliability.

Besides being notorious for poor documentation and weak support, the USPS APIs are well known among developers for having chronic downtime issues.

So, if the USPS API system isn't reliable, what's a developer to do? Fortunately, there are a number of available address validations services, in addition to the USPS.

Address Validation Software

When it comes to address validation software, the USPS focuses on putting address data together, NOT on sharing it. Therefore, third-party companies create address validation software that allows you to use the USPS database info in a more effective way than the USPS does. Many of these companies take the data from the USPS and combine it with supplemental information they feel would be helpful to their customers. Most of these providers make this augmented data available through APIs.

What each provider's API does or doesn't do varies, as does its ease of use, uptime, tech support, and so on. Each provider has something to bring to the table, and we've highlighted a few of the most popular ones in this article, discussing the pros and cons of each.

The short version is this: the USPS has the most up-to-date data, Melissa Data provides the most supplemental information, Loqate has the most thorough international data, and SmartyStreets is the fastest and easiest to use address validation software.

Note: Since this article deals with APIs (which are used to validate addresses then give them back to you), it may be helpful to brush up on terms like "uptime" and "documentation."


The proud men and women in blue shorts are the authority when it comes to shipping in the United States. Their data is always up to date because it comes to them first. They keep track of virtually every mailable address in the country—and with 153,900,000 delivery points in the US, that's no small feat. They handle the deliveries, and they keep track of where everything is going.

In short, they do all the hard work.

The USPS has recognized that the information they've aggregated is worth something to the rest of the nation, and they've made it available in a number of ways. For starters, they have a Web Interface that can validate an address for you, free of charge, right on their website. It's a simple little gizmo that lets you enter addresses one-at-a-time, and gives you a quick thumbs-up/thumbs-down for validation. They also have an API that provides address validation services.

The USPS solutions (their Web Interface and their API) would be well suited for anyone with an address validation job that's not system critical, not time sensitive, not high volume, and will result in packages being sent via the USPS (as per their API's license agreement). In other words, if your needs are standard and simple, you can have this done for free.

But if you're reading this article, we have a feeling that your address validation needs are a little more extensive. Maybe you need something easier to use, or something more reliable for your mission-critical applications. Keep reading, and we'll tell you about some companies that make the USPS's blood, sweat, and tears easier to access.

Melissa Data

Melissa Data serves a clientele that is largely composed of big businesses. Because they're a larger organization serving larger companies, they offer a breadth of supplemental information. They go well beyond USPS's "Yes or No" model, offering things like email and name validation, demographics, and even census and weather information on addresses that are processed. Essentially, you hand them what you want validated, and they hand you back an encyclopedia entitled, "Everything you wanted to know about this address, but were afraid to ask."

Their API is fairly straightforward and easy to use, and their uptime is pretty darn great. They have a tech support team to help answer your questions, and their documentation is easier to understand than what the USPS offers.

If you're looking for real in-depth, gotta-know-everything kind of information, Melissa Data is a solid choice.


Loqate's primary selling point is its accuracy—both in domestic and international service. For them, the USPS is only one of many data providers. Their API offers access to insanely accurate addresses and geocodes for more than 240 countries.

Loqate is a good solution for someone who is highly skilled at reading technical documentation and can work well independent of hand-holding from customer service.

Their claim to fame, in a nutshell, is the aforementioned data accuracy. In fact, they're often used as a database by other validators much in the same way that the USPS is, just for foreign addresses. So if you're looking for someone who can get you GPS coordinates accurate enough to find your favorite restaurants from Amsterdam to Zimbabwe, you might consider putting your money on Loqate.


At SmartyStreets, we believe that things should be fast and simple. Kind of like teleportation in sci-fi movies: push a button and—poof!—you're where you want to go. We don't have Scotty to beam us up. But we do have the fastest turnaround times in the address validation industry. Our online APIs and our Command-Line Interface can process hundreds of thousands of addresses in minutes (single-digit minutes) instead of the days of turnaround that some companies take to get your data back to you. At speeds like that, your validation is nearly instantaneous, and with one-at-a-time lookups, it's so close to instantaneous you might think you're using an infinite improbability drive.

Our API is also among the easiest to use. That's our specialty: we take complicated things and make them simple. You can have our API plugged into your own programs in a matter of minutes (single digits again). Operating the API is streamlined and intuitive. Our uptime is also one of the best (there's lots of 9's in the percentage). We also provide a fully self-hosted, on-site, on-premises, local solution available to clients. And in case your redshirts encounter any problems, we have extensive documentation for self-help. There's also a direct phone line to our tech support crew, where real-live human beings are happy to speak with you.

We offer validation and geocoding for US and international addresses, and our prices are easier to stomach than many other companies. Most of all, though, we put a lot of effort into getting you off the ground quickly and keeping you running reliably.

SmartyStreets is despicably reliable, at stomach-turning speeds. We may have a narrow focus, but we can still make the Kessel Run in under 12 parsecs.

Best Address Verification Software?

So which of these companies has the best address verification software? As with many things in life, there's no one-size-fits-all answer here.

This article has included a brief sampling of some of the more prominent address cleansing service providers. There are other, more obscure providers, and if none of us on this list fit your needs, hopefully you can still use our information and examples to hunt down one that does. Each business is going to have areas where they've sacrificed a little to be the best in their particular area of focus.

The best thing to do is visit each provider's demo pages and try out their APIs for yourself.

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