Each API contract should possess one or more tags providing words and phrases that accurately represent the purpose and intent of an API contract. As with other contract metadata, the tags should reflect the contract level, and not each individual API within the contract.
Ideally the tags you apply to the contract are defined as part of an overall vocabulary that is defined as part of the contract, but likely applied across many API contracts. Having a program level vocabulary helps organize contracts by domain, line of business, or other meaningful bounded context.
API contract tags help make contracts more discoverable and able to be organized and reported upon in useful ways. Taking the time to make sure each contract has tags that represent the contract, APIs, but also stakeholders is how you begin to do the work to tame the sprawl that exists across the average enterprise.