One of Yosuke Kobayashi's biggest headaches has been finding enough workers to build hotels, restaurants and bath houses for his construction company.

That was until the manager at construction company Luckland Co. found Sukedachi, a mobile app that connects contractors and tradespeople. Nowadays, he's hiring carpenters, painters and glaziers with just a few taps on his smartphone.

Japan is in the middle of a building boom, thanks to infrastructure projects, a shortage of hotel rooms and the 2020 Tokyo Olympics around the corner. That's fueling the tightest labor market in a generation, with 4.3 jobs available for every construction worker, according to the labor ministry. The industry is woefully inefficient; workers usually find gigs via referrals, word-of-mouth and printed job listings.