The only measure that truly matters in this trying rebuild season for the Toronto Blue Jays is in the development of their key young players, the kids being counted on to one day form the core of a contender.

In that vein, the most important points of progress with the all-star break nigh after a long, trying first half:

• Danny Jansen opened the season as the primary catcher and did enough as a defender to ride out a cold spell at the plate to eventually get right;

• Lourdes Gurriel Jr., opened the season as the starting second baseman, was sent down, and returned as a monster-mashing left-fielder;

• Vladimir Guerrero Jr., broke through to great fanfare and while he hasn’t set the world on fire, he’s more than held his own, even through a recent dry spell;

• Cavan Biggio has looked like he belongs almost from the moment he arrived;

• Trent Thornton has the stuff to be a part of this.

Teoscar Hernandez, Rowdy Tellez and Brandon Drury have, thus far, been less consistent. Ryan Borucki, meanwhile, has been injured, although GM Ross Atkins said Saturday that he could be another rehab start or two from returning.

For all of them, 2½ months remain to either cement gains, or alter trajectories, as the jockeying for a place on the 2020 team, and spots on the projected rosters beyond is the ultimate point of this type of season.