The phrase "a mighty tool" is correct and usable in written English.
It can be used to describe something that is powerful or effective in achieving a particular purpose or task.
Example: "The new software is a mighty tool for improving productivity in the workplace."
Alternatives: "a powerful instrument" or "an effective resource."
This is a mighty tool that has room for creative ideas to manifest themselves into the next Angry Birds or Instagram.
Technology is a mighty tool with great possibilities, but, at present, it is often poorly used and serves more to stifle intellectual curiosity than to promote it.
"In a world that is torn by wars, fanaticism, and devastation, art is a mighty tool that helps us fight extremism," so said Jimmy Keyrouz '16SOA, whose MFA thesis film Nocturne in Black, produced by Felecia Hunter '16SOA, received the Student Academy Award from the Academy of Motion Picture Arts and Sciences.
No one (read as I didn't do research) knows why this soup is such a mighty tool in the fight against world-enders but it is.
New Straits Times, 1 November 2007 The pen's a mighty tool to combat illiteracy KUALA LUMPUR: More than 115 million children worldwide, mostly in developing countries, will remain locked in the cycle of poverty because they can't read and write.
In the numerical scale of power devised by Thad Beyle, a political scientist at the University of North Carolina, only Massachusetts' governor has a mightier tool kit.
The tax deduction has been a mighty powerful tool in getting people to be generous.
A lightbox is a mighty handy tool.
The Internet may be, as one Texas judge said, "a mighty powerful tool".
The wonderful thing about the digital revolution is that Trump has no monopoly on this vast and mighty tool; it is in everyone's pocket.
"See how he is able to take stone away from me with just a few blows of his mighty tools.
