Relationships API

BuiltWith Relationships API

Find relationships between websites and website IP and tag history


Get XML and JSON results of relationships between websites that show what sites are linked together, by what and for how long.

The general access method is as follows -[xml|json]?KEY=[YOUR KEY]&LOOKUP=[DOMAIN]


You must provide your API key in each lookup. See the examples for how this works.

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Get Domain Example

XML Get Single Domain[YOUR KEY]&

JSON Get Single Domain[YOUR KEY]&

CSV Get Single Domain[YOUR KEY]&



The following GET parameters can be supplied for lookups

Name Examples Required
KEY 00000000-0000-0000-0000-000000000000
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Domains and sub-domains work with the Relationship API (not internal pages)

Multi-Lookup Option
When doing RAW domain lookups, you can parse up to 16 domains at once as a CSV. For example,, - this dramatically improves throughput.


The Relationship API will respond with a document in the format -


Results is the top level response that identifies the lookup.

Name Example Description
Domain The domain that was looked up.
Identifers Identifier explained below Explained below

Identifiers are the unique codes that are found on the domain and other domains that also have it.

Name Example Description
Type google-analytics The type of identifier See all Types
Value 454517 The value of the identifier - typically the code of the identifier like an IP address or an account id.
First 2013-03-26T13:00:00Z The date we first detected this identifier
Last 2016-04-23T14:00:00Z The date we last detected this identifier
Matches Match explained below Explain below

Matches are other domains that have this identifier.

Name Example Description
Domain The domain name of the match
First 2013-03-26T13:00:00Z The date we first detected this on the matched domain
Last 2016-04-23T14:00:00Z The date we last detected this on the matched domain
Overlap true If this domain used the identifier at the same time as the lookup Domain

Code Examples

JSON/XML have integrations in all modern programming languages. Here's some StackOverflow topics for various languages - Python, C#, Java, PHP, C++, TSQL and Ruby.

Error Codes

Note error messages in this format cannot be guaranteed, your implementation should also consider non-200 response codes as errors. The Lookup property will be null (json) or not provided (xml) if the error is server related. View all potential well-formed error codes.

Terms of Use

Our standard terms cover the use all of our APIs.

In general, you can use the API to enhance your product in many ways. The only limitation is you cannot resell the data as-is or provide duplicate functionality to and its associated services.