Most notably, the contracts also will punish time-honored tactics that bloggers have used to avoid censorship, like disguising comments on censored topics by using homonyms (where two different Chinese characters have nearly identical sounds), puns and other dodges.

To evade censors, bloggers have referred to the dissident artist Ai Weiwei by using the Chinese characters for “love the future,” a rough homonym of his name. Such ploys would be punished with a loss of points under the new rules.

Sina officials left unclear how many points a user would lose for a specific violation. But they said that microbloggers could increase their score to 100 points by supporting unspecified promotional activities, and would receive “low credit” warnings should their total fall below 60 points.

The restrictions are not new by themselves. Government censors already control what appears on the Internet, and corporate minders at Sina Weibo and other sites have long complied with their orders, deleting offensive comments, sly homonyms and other posts that rile the government’s sensibilities.

The point system, however, appears to be a muted effort to extend that control by warning users when they approach the boundaries of official tolerance. Internet companies like Sina that are privately operated tread a thin line between too-lax censorship that might draw government punishment and overly strict rules that would quash the lively debates that make the services popular.