EBay is removing some fees for using APIs (Application Programming Interfaces) in its web services-based eBay Developers Program.

The scheme allows developers to build sites that drive transactions on eBay, and then get paid by eBay. Alternatively, developers can build software that is used by sellers as front ends to eBay, whereupon developers are paid by sellers. About 22 percent of the site's listings are generated through these third-party applications.

Previously, fees have been charged for using APIs to access the scheme. "We really wanted to build on the past success we've had. We tried to identify the barriers to innovation on the eBay platform, and the cost was one of those barriers," said Greg Isaacs, director of the eBay Developers Program.

The free API usage applies to developers using the unified schema eBay announced last February. API calls made using legacy schema will be supported until next June and will continue to be charged at previous call rates. This provides an incentive to move to the unified schema, eBay said.

EBay has charged $1.25 (about 72p) per 1,000 APIs calls as a starting rate, or annual fees starting at $500 (£288). But these no longer apply to unified schema users, as do certification fees paid to eBay employees to verify the efficiency of applications before they go online. Developers can promote their application in the eBay Solutions Directory, for third-party set-ups designed to enhance selling on eBay.

Isaacs would not disclose how much revenue eBay would sacrifice by eliminating these fees, but he pointed out that this revenue has never been important to eBay, and that revenue from buyers and sellers is what counts.

Also on Monday, eBay will launch a contest called the eBay Developer Challenge 2006, intended to inspire developers to build software that supports the eBay marketplace, Isaacs said. To be judged by a panel of the company's employees, the contest will have winners in the individual developer and collaborative development categories. Runners-up will be named as well.

The winner of the individual category will win $500 (£288) and a free trip to the O'Reilly Emerging Technology Conference in San Diego next March.

Begun in 2000, eBay's developer scheme is supported by about 21,000 developers, half of whom have joined in the past year.