at one's fingertips

Definition 
Ready, instantly available; at one's command. The term refers to both cognizance and competence—that is, it can mean either knowledge or the ability to carry out a task. Presumably it is based on something being as close at hand and familiar as one's own fingers. Its roots may lie in an ancient Roman proverb, "To know as well as one's fingers and toes," which in English became one's fingers' ends (in the proverb collections of John Heywood, John Ray, and others). Fingertips appears to have originated in the United States in the nineteenth century.