How do you estimate the supply/demand of your career?

For me, to plan one's career, they need to know what rules/skills/tools are becoming in high demand, and also what roles/skills/tools are becoming easy and commoditized so there is a huge supply/competition, One can check Linkedin/Indeed/etc manually to gauge demand, but I am sure there are better ways, also how do people check what skills are becoming crowded to run away from?