What is the test for a pro se pleading in a civil rights case?

While plaintiff alleges defendants violated his rights, he provides no factual context stating how defendants violated his rights. He fails to state facts showing when these incidents occurred, what occurred, and how each named defendant participated in the alleged deprivations. Although pro se pleadings are liberally construed, Haines v. Kerner, 404 U.S. 519 (1972), conclusory and vague allegations will not support a cause of action. Ivey v. Board of Regents of the Univ. of Alaska, 673 F.2d 266 (9th Cir. 1982). Even a liberal interpretation of a civil rights complaint may not supply essential elements of the claim that were not initially pled. Id. at 268.