How to Do a ZIP+4 Lookup with ChatGPT (and Catch Bad Addresses Before You Ship)

Check a customer's address against USPS before you ship. Try TinyFish free. New accounts start with $8 in Wallet funds.

TL;DR

• A ZIP+4 lookup tells you the full nine-digit ZIP Code for an address, plus the address written the way USPS standardizes it.
• With the TinyFish app in ChatGPT or Claude, one prompt opens the official USPS ZIP Code Lookup, enters the address and reads back the result.
• If USPS can't match the address, the agent tells you, which is exactly what you want to know before a package goes out.
• It's read-only and needs no login.

A quick disclosure: I work at TinyFish, which gives ChatGPT and Claude live web access, including a browser agent that can open sites like USPS ZIP Code Lookup for you.

What ZIP+4 is, and why it matters for a small shop

A regular ZIP Code has five digits. A ZIP+4 adds four more after a hyphen, like 12345-6789. USPS explains that the first two of the extra digits point to a sector or a few blocks, and the last two to a segment, such as one side of a street (USPS FAQ: ZIP Code, The Basics). The ZIP+4 was introduced in 1983 so mail could be sorted to a specific group of streets or a high-rise building (USPS).

For a small business, the useful part isn't the extra digits on their own. It's the check that comes with them. When USPS can match an address and return a standardized version with ZIP+4, you know the address exists in its system. When it can't, something is off: a typo, a missing suite number, or an address too new to be listed.

That matters because a bad address costs you twice. USPS returns packages it can't deliver because part of the address is "missing, incomplete, or incorrect", and the sender has to reship with new postage (USPS FAQ: Where is my package?). USPS also notes that improperly labeled mail can move more slowly and may be returned (USPS FAQ). A ten-second check before you print the label is cheaper than a returned order and an unhappy customer.

What you need

• ChatGPT or Claude with the TinyFish app installed. Follow the plugin docs once, then you just ask in plain English. TinyAgent, TinyFish's browser agent, opens the site in a real cloud browser and reports back.
• The address you want to check: street, suite or unit, city and state.

The USPS ZIP Code Lookup is public, so there's no login and no saved profile to set up.

How to do a ZIP+4 lookup with ChatGPT

Here's the tested prompt. Replace the part in brackets with the address.

Use TinyFish to check this address on the USPS ZIP Code Lookup: [street, suite, city, state]. Give me the standardized address with ZIP+4, or tell me if USPS can't find a match.

Filled in for an invented example business, a stationery shop called Paper Lantern Co. checking a wholesale customer's address before shipping (the address is made up too):

Use TinyFish to check this address on the USPS ZIP Code Lookup: 410 north maple ave ste 3b, springfield, il. Give me the standardized address with ZIP+4, or tell me if USPS can't find a match.

Notice the address is typed loosely, all lowercase with abbreviations. That's fine. Getting the tidy USPS version back is the point.

When an order looks odd, add a second step in the same chat:

Compare the standardized USPS address with the address my customer typed at checkout:
[address from the order]. List every difference, such as a missing suite number,
a different street suffix or a different ZIP Code.

Why read-only matters

The prompt only asks the agent to look something up and report. It doesn't sign in, buy postage or change anything. It's safe to run as often as you like, on any address, before you commit to a label.

Watch it run in ChatGPT

Here is the tested prompt running in ChatGPT with the TinyFish app, sped up. You can see TinyFish open the site in a live browser, then ChatGPT write up the answer.

What you get back

For each address you get one of two answers:

• A match: the standardized address as USPS writes it (usually in capitals, with standard abbreviations like AVE and STE), the city and state, and the full ZIP+4.
• No match: a plain statement that USPS couldn't find the address, so you know to check it before shipping.

Example output (invented business):

The first one is ready to ship. The second one gets a quick email to the customer before anything goes in the mail.

Tips

• Include the suite or unit. Apartment and suite numbers are the most common thing missing from checkout forms, and they change the ZIP+4.
• Spell out the city. USPS says city names should be written out completely, since abbreviated city names are often marked unacceptable (USPS FAQ).
• Do one, or a few, at a time. One address per prompt is the most reliable. For a handful of orders, run them one after another and collect the answers in one table.
• Check before Black Friday week. A batch of new customers means a batch of new addresses. Check the ones that look unusual before you print labels.

When it doesn't work

• "USPS can't find a match." That's an answer, not a failure. USPS says this can happen when an address is entered incorrectly, is invalid, or is a new construction address or new development (USPS FAQ). Check the spelling and suite number, then ask your customer.
• It reads what USPS shows, nothing more. The agent doesn't know if your customer has moved, or whether someone is home to receive the package. It only reports what the lookup returns.
• New streets can lag. USPS notes that changes to its national ZIP Code data can take 30 to 60 days to appear in the lookup tool.

Want to see this live? We're running it at TinyFish Small Business Week, a free 45-minute live session on Thu Nov 19, 11 AM ET. Save your seat, and bring the job you want off your plate.

What it costs

New TinyFish accounts start with $8 in Wallet funds, no card needed. Agent runs are billed per step, at $0.016 per agent step. Once the package is on its way, you can track it with ChatGPT too.

Catch bad addresses before they become returned orders. Start free on TinyFish.