As charities increasingly deal with donors who expect more control over how their money is spent, a large humanitarian relief organization has developed a new online tool to give supporters a bigger say.

Direct Relief, which concentrates on medical aid for emergencies and poverty-stricken regions, is testing a new online donor site, as the annual year-end giving season approaches.

Currently, the group's donation Web page allows donors to choose from one of two broad options. They can click to let Direct Relief use their gift where it is "needed most." Or, they can use a drop-down menu to have their donation directed to one of several program areas, including efforts focusing on Hurricane Matthew, the Zika virus and the Syrian refugee crisis.

Under the new system, donors can use a slider tool to apportion their gift among several options with greater specificity. The tool will set a suggested allocation, but donors can change it as they wish. For instance, if donors give $25, they could choose to have it all go to "emergency preparedness" or another broad category. Or, they may choose to divide it up into smaller chunks: $10 to Hurricane Matthew, $10 to Zika and $5 to "improving health in vulnerable communities." (Donors can still click to have money go where it's "needed most.")

The new tool also has a line item for "fundraising," said Tony Morain, a Direct Relief spokesman who helped oversee its development, with the default donation set at zero.

The new system is expected to be fully operating by early December. Initially, some visitors to the site will see the new page, while others will still be directed to the current donor page, so Direct Relief can assess donor preferences and fine-tune the tool, Morain said.

The approach is part of a larger trend toward greater flexibility and transparency at nonprofit groups, driven by new technology as well as wariness by donors. In recent years, some major charities have faced criticism for using donations collected after major disasters for other purposes, or spending too much on fundraising and overhead costs.

"We're hopeful it will instill more trust," and so increase financial support over the long term, said Thomas Tighe, chief executive of Direct Relief. "Fingers crossed."

Sandra Miniutti, vice president of marketing at the nonprofit evaluation site Charity Navigator, said Direct Relief was one of its most highly rated charities. She said she hadn't seen its new donor tool, but she couldn't think of another site offering such detailed online options for donors.

But Miniutti cautioned that setting the default donation for fundraising costs at zero might give the impression that fundraising was unimportant.

While donors may prefer to have their money go directly to specific programs, she said, the reality is that all charities have to raise money, pay employees and cover mundane costs like electricity bills. If you have researched a charity and are comfortable making a donation, she said, it's best to give without restrictions, to allow the charity as much flexibility as possible.

Morain said Direct Relief was able to try different strategies with its donor page because it currently had a bequest to cover its fundraising budget. "It's a bit of an experiment," he said.

Ann Carrns writes for the New York Times.