Fixed and mobile Internet providers must offer free trials of Web filtering tools to block out objectionable sites by the end of next year.

The move is part of the Media Development Authority's (MDA) plan to improve parental controls as the popularity of mobile devices gives the young easier and quick access to dubious websites. The move will also address a "low" awareness of the availability of Web filtering tools, said the MDA.

The one-time free trial will last for six months or half the term of a subscriber's contract, whichever is shorter. Internet service providers (ISPs) must get subscribers' consent before charging them after the trials. The rule comes after a four-week public consultation last year. ISPs typically charge $2 to $5 a month for such a service.

"The duration of the free trial period should give parents enough time to try out and assess the usefulness of the Internet parental controls," said the MDA in a statement released yesterday.

It had earlier proposed a free basic service instead of a free trial.

The decision to go with a free trial would allow ISPs to offer more comprehensive functions - such as monthly reports on the websites visited - to better meet the needs of parents, the MDA said. It will require ISPs to block content containing sexually explicit materials, violence and gore by default.

Since February 2012, it has been compulsory for ISPs such as Singtel, StarHub and M1 to actively promote Internet filtering tools to new or repeat subscribers of fixed broadband plans.

It was extended to mobile subscriptions in June that year.

ISPs which flout the rules can be fined, suspended or have their class licence cancelled by the MDA. So far, none has been warned or punished.

Subscriptions to these tools are still described by the MDA as low - only 100,000. Some parents contacted by The Straits Times welcomed the new rules, but others were concerned that the fee for the filtering service would go up.

Realtor Eelaine Ng, 40, whose two sons aged four and six have chanced on dirty dancing videos on the YouTube portal, said: "I hope the ISPs don't raise prices after the trials are over."

But there are limits to what basic filters can do. For instance, they may not be able to filter objectionable videos, games and apps on valid sites like YouTube or Google Play. IT firm director Michael Tan, 45, said: "The effort has to come from parents and caregivers to educate the kids on what they should or should not view."