Many applications depend on a web service to deliver data and fetch their configuration using HTTP.
In most cases, this is done using a REST API.
Clients that make HTTP requests in the REST fashion are dependent on a (sometimes) strict contract.
Especially after deployment, breaking an API contract can be fatal to business operations.

A basic tool can be useful in verifying the correctness of the web service your application uses.
When running ContractPolice on a regular basis, you can make sure to work with valid APIs.