Sydney - Head coach Jacco Verhaeren wants a hard competitive edge from Australia's swimmers at Budapest's World Championships as his team looks to rebound from last year's under-performing Rio Olympics. 

The 'Dolphins' want to up their game when the world championships start on Sunday after winning three gold medals, four silver and three bronze in Rio, but well under their tally projections after going into the Olympics with eight world ones. 

Not one of those top rankings was converted into an Olympic gold medal as world leaders including Cate Campbell and Cameron McEvoy succumbed to the crushing weight of home expectations.

Australia finished second on the swimming medal tally, but was a distant 23 medals away from the dominant United States with their 16 gold, eight silver and nine bronze. 

Olympic 400-metre freestyle champion Mack Horton is back to renew his feisty rivalry with Chinese superstar Sun Yang and Emily Seebohm, Mitch Larkin and Bronte Campbell will be defending their world crowns in Hungary. 

But Rio 100m freestyle gold medallist Kyle Chalmers is recovering from heart surgery and is missing along with team elders Cate Campbell and James Magnussen, who are taking time out.

Dutchman Verhaeren has switched Australian swimming's approach to international competition with important lead-up meets scheduled closer to the bigger events in a bid to toughen up his swimmers. 

"We certainly had some great wins (in Rio), but we also had some losses, undoubtedly," Verhaeren said. 

"That's why it's very important to approach every tournament we go to - this year's world championships, next year's Commonwealth Games and Pan Pacs - in the most serious way to be able to step up on the big stage. 

"Although it's not an Olympic year, the goal for the team, and most certainly for the individuals, is always to try and show your peak form at a major event. 

"Performing under pressure, dealing with those circumstances, is most welcome." 

Horton, who became one of the biggest stories of last year's Rio Games when he called out Sun Yang as a "drug cheat" before their 400m freestyle final, will hold much of Australia's hopes in Budapest. 

"Mack is looking forward to it," Swimming Australia chief executive Mark Anderson said. 

"He's in good form. Not only in the 400m but the 1500m. There will be great entertainment in both of those races and the swimming world will be watching with interest." 

Horton claimed a rare treble at the Australian nationals, winning the 200m, 400m and 1500m freestyle to match Grant Hackett's effort from 2008 and is looking to swim the events at the worlds.

"I am keen to do it in Budapest, it will be like taking it back to the (2013) junior worlds, so there's no need to over-complicate it," Horton said. 

"I don't think I was prepared for it in Rio, but now I feel like I am." 

After an underwhelming Rio Games, McEvoy is chasing his first world title and snatched his fourth national crown from Olympic champion Chalmers back in April. 

There are 13 rookies on the Australian team, which has an average age of 21. 

Ariarne Titmus, a 16-year-old from Tasmania, completed the 400-800m freestyle double at the nationals, and finished runner-up behind Emma McKeon in the 200m, earning herself three individual swims in Budapest. 

"From a rookie point of view it's very exciting for us," Verhaeren said. "They qualified with excellent times. The qualifying standard is pretty tough here in Australia."

It will be backstroker Seebohm's sixth world championships, while breaststroker Larkin will compete at his fourth worlds. 

Most of the Australians have been racing in grand prix events in Europe ahead of the Budapest showpiece as part of a new approach to major meets set in motion after the Rio Olympics.