A Dutch startup is launching an app that will allow people to give legal consent to sex via their mobile in an initiative spurred by Sweden's plans to bolster its rape law.

The LegalFling app, which lets users set out which practices they are and are not comfortable with, records sexual consent in a legally binding agreement.

"Sex should not only be fun, but also safe," LegalFling creator Rick Schmitz, chief executive of tech company LegalThings, told the Thomson Reuters Foundation on Thursday.

"You're not going to ask someone to sign a contract before sex; LegalFling is an easy way to clearly set and communicate rules and boundaries before having sex."

Response to #MeToo, legislation

The app's creators said they came up with the idea as a practical response to Sweden's proposal to introduce legislation requiring explicit consent for sexual contact later this year.

The launch — due in three weeks — comes amid heated public debate over issues around consent triggered by the #MeToo social media campaign against sexual harassment and assault which has seen a slew of allegations against Hollywood stars.

"No means no". Always. LegalFling doesn't change that. The app is about setting clear rules and boundaries at forehand and making sure they are followed. <a href="https://t.co/yMKCgPyg8f">pic.twitter.com/yMKCgPyg8f</a> —@livecontracts

The app uses blockchain, the technology behind the cryptocurrency bitcoin, making it impossible for anyone to tamper with the agreement.

Users can stipulate sexual dos and don'ts as well as rules on the use of condoms, disclosure of sexually transmitted diseases and the taking of photos and videos. The app allows both parties to agree on a penalty if footage is shared.

Acts of revenge porn if the relationship broke down would be a breach of contract and easy to take to court, the developers say.

Ethical questions raised

The idea of such an app was ridiculed by actress Catherine Deneuve and other French women in a recent open letter which said the #MeToo campaign had gone too far and Sweden's plans "bordered on ridiculous."

"Next thing you know, two adults wanting to sleep together will have to specify beforehand, via an app ... which practices they do and don't consent to," they wrote, apparently unaware of LegalFling.

Other commentators have raised concerns about the ethics and workability of the app.

Writing on tech site Gizmodo, journalist Melanie Ehrenkranz said consent was not a "one-time checklist" but should occur continually throughout a sexual encounter and could also be withdrawn.

The LegalFling website states users can change their mind and withdraw consent through the app.