The phrase "indispensable tool" means something that is absolutely necessary or essential for a particular task or purpose. It refers to something you cannot do without because it is crucial and needed. Full definition
Seen as an increasingly indispensable tool for coping with the ever - growing amounts of data which they handle in managing complex tasks, AI has arrived in the legal sector a big way. (barristermagazine.com)
The modern smartphone and, to a lesser extent, the tablet have become indispensable tools in the management of your practice. (blog.ulawpractice.com)
It's an almost indispensable tool that players will undoubtedly use before every mission. (playstationlifestyle.net)