Critical Mistakes in Your Robots.txt Will Break Your Rankings and You Won't Even Know It
Bing's new robots.txt tester can help SEOs identify crawling issues
A Complete Guide to Robots.txt & Why It Matters
A Guide to Robots.txt - Everything SEOs Need to Know - Lumar
GSC's Robots.txt tester can be wrong -
Glenn Gabe on Twitter: "Quick reminder that your robots.txt directives require a user-agent to be specified. If you quickly add a disallow directive w/out it having a user-agent, those urls will not