The phrase "one's primary tool" refers to the main or most important thing that someone uses to achieve a particular goal or task. It is the key resource or instrument that they rely on the most. Full definition
While trends may change, right now smart phones and QR codes aren't primary tools for recruiters. (robinresumes.com)
However, the use of predictive coding and other advanced forms of technology assisted review (TAR) as primary tools in disclosure reviews remained at reasonably low levels coming into 2016. (newlawjournal.co.uk)
The best sign of how big a problem filing by mail can be in getting your refund quickly comes from the instructions to the IRS's primary tool in telling taxpayers when to expect their checks. (fool.com)