Developers will pay a minimum monthly subscription fee of US$40, Microsoft said. It will collect the fee through the Windows Azure Marketplace, where the API will be hosted. All users will move to the pay-per-use regime within a few months, it said.

The Bing API allows developers to incorporate Bing search results into their applications. Microsoft said the changes will give them "fresher results, improved relevancy and more opportunities to monetize their usage of the Search API."

The change will involve "a new API end point, moderate changes to the request and response schemas, and a new security requirement," Microsoft said.

Bing's share of the search market recently hovered at around 15 percent, according to comScore. Google, which gets a dominant 66 percent of all search queries, already developers who make more than 100 queries a day to its search API.

The IDG News Service