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Use the developer tools in the Develop menu in Safari on Mac
If you’re a web developer, the Safari Develop menu provides tools you can use to make sure your website works well with all standards-based web browsers.
If you don’t see the Develop menu in the menu bar, choose Safari > Preferences, click Advanced, then select “Show Develop menu in menu bar.”
For a description of the commands in the Develop menu, see Safari Developer Help.
See alsoSafari for Developers