"That is at the top of our list of things we care about," he told venture capitalist Jamie Montgomery during an on-stage conversation at the Montgomery Summit technology conference in Santa Monica late Wednesday afternoon.
Snapchat, he said, has aimed for workers to feel comfortable even when barraged by feedback that's potentially hurtful.
"It's not enough to not be mean," he said. "You've got to really, really try to be kind .... If you don't have that environment of kindness, there's just no way you can expect people to grow at the rate they need to cope with a business that's changing quickly."
Beside kindness, Spiegel pointed to hard work and creativity as "baseline" traits needed to work at Los Angeles' most valuable technology start-up.
Following what a source said on Wednesday was a $200-million investment from Chinese Internet giant Alibaba, Snapchat is now valued at an estimated $15 billion. Montgomery told the audience he wouldn't ask Spiegel about the funding.