Comment and Uncomment Code
Ctrl+Alt+/ / Ctrl+Shift+/
With JetBrains Rider, a single keystroke is enough to comment or uncomment code.
Comment and uncomment with line comments
If there is no selection, JetBrains Rider will comment the current line, or uncomment if the line is commented, and moves the caret to the next line.
According to the Don't indent comments started at first column option, the comment will be added with or without the indent. You can configure this option for different languages separately, for example, for C# it is on the page of JetBrains Rider settings Ctrl+Alt+S.
If there is a selection, JetBrains Rider will comment or uncomment all the lines that the selection spans. Even if a line is partly selected, the comment mark is inserted in the beginning of this line.
An alternative way to uncomment any line comment is to set the caret at this line, press Alt+Enter and choose Uncomment.
Comment and uncomment with block comments
If there is no selection, JetBrains Rider will create an empty block comment at the first whitespace that follows the current caret position.
If the caret is within a block comment, the block is uncommented.
If there is a selection, JetBrains Rider will add block comment marks in the beginning and in the end of the selection. The caret is moved to the end of the block comment.
An alternative way to comment any block of code is to select it, press Alt+Enter and choose Comment selection. The same way works for uncommenting code inside a block comment - set the caret anywhere in the block comment, press Alt+Enter and choose Uncomment.