The term “number lookup API” can cover at least five different products that return five various things, and selecting the wrong one is a common reason a phone data project underdelivers. This guide breaks down what each type of number lookup API returns, and what kind of information you’ll receive from each.
What is a Number Lookup API? #
A number lookup API is an endpoint that takes a phone number as input and returns structured data about that phone number. Depending on the product, that data can include whether the number is valid and assigned to a carrier, the line type, the carrier name, the name and address of the subscriber, or a score describing recent activity on the line.
The term is used loosely. A carrier lookup, a reverse phone lookup, a CNAM lookup, and a phone validation check are all “number lookup APIs,” but they query different data and cost different amounts per API call. For example, our Phone Validation API returns metadata and activity insights, Reverse Phone API for comprehensive identity enrichment, and Caller Identification API to find the single best identity.
How Does a Phone Number Lookup API Work? #
You send a phone number to an HTTPS endpoint with your API key. The provider resolves the number against their data, then returns JSON.
Our Reverse Phone API request looks like this:
GET https://api.trestleiq.com/3.2/phone?phone=[insert_phone_number]Optional hints help narrow down the result, including phone.name_hint, phone.postal_code_hint, and phone.country_hint. These let you tell the API what you already believe about the record so we can rank owners accordingly.
If you would rather not write code, our APIs are also available through Batch Upload for CSV processing, and through partner integrations such as HubSpot, Clay, Snowflake, and ActiveProspect.
Which Number Lookup API Should You Use? #
Match the product you select to the decision you’re making.
| Goal | Product | What’s Included in the Response |
| Confirm a number is real and reachable. | Phone Validation API | Validity, carrier, line type, Phone Activity Score. |
| Know who owns a number, plus address and demographics. | Reverse Phone API | Phone metadata, owner names, demographics, and current address. |
| Know the person behind the inbound call. | Caller Identification API | Phone metadata, single best name, demographics, current address. |
| Verify whether a person’s name, phone, address, email, and IP belong together and if they can be contacted. | Real Contact API | Verification of phone, email, address, IP, and Contact Grades. |
How Do You Test a Number Lookup API Before You Commit? #
Test against known outcomes. Here are some good rules of thumb:
- Pull a real sample, not a clean one. Use records straight out of the source you buy or collect from, including the bad ones. A hand-picked list of numbers you know are good will make every vendor look identical.
- Size the sample so the results mean something. Small files product swings that have nothing to do with vendor quality.
- Score coverage and accuracy separately. Count how often you got a value, then count how often that value matched your truth set. Averaging them can hide the results you care about.
- Test an attribute you’ll actually create rules for. If you need to determine whether to call or text certain numbers, benchmark line type. Name coverage is irrelevant to that decision.
- Run it against your disposition data. Connected calls, returned leads, and bounced records are the only truth set that reflects your business.
How Do You Start Using a Number Lookup API? #
If you know which attribute your decision depends on, select the product that returns it and test your own file. If you’re not sure yet, Reverse Phone API returns the widest set and lets you narrow it down from there.