Bold or italic in C# or VB documentation comments?

This feature is now available in Visual Studio 2019 version 16.3.0 (release notes).

• You can use the <i> or <em> tags for italic.
• You can use the <b>or <strong> tags for bold.
• From the release notes, a variety of html tags seem to be supported, but the official documentation doesn't seem to be updated with this new feature just yet.

It looks like this: .

OP's note: This was the accepted answer before 2019 Visual Studio update after which I accepted the other answer. This one is still useful and valid for users without that update.

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Not strictly, no. However, Sandcastle (a documentation generator that generates HTML from the documentation) supports to just use HTML in there, so you can use <em> and <strong> just fine if you build it with Sandcastle.

To put it another way: As Jamiec already notes, XML documentation comments are just XML. So you can put any valid XML in there; the compiler will happily write that into the documentation XML file. It all depends on the software that processes that file. Sandcastle just passes anything it doesn't know on as HTML, since that's its output format anyway.

Visual Studio will simply ignore them when displaying the help tooltip:

ReSharper in its Ctrl+Q view will show HTML tags as text which makes things a bit ugly:

Those are usually only of concern to you if you author a library to be used by others, though. But it also means that within the IDE no one can see your emphasis as intended.

I have found actually little need for emphasis when writing API documentation; oftentimes you can write a sentence differently or restructure to have important nodes in a separate paragraph near the end, to not need emphasis at all. Consistent language and phrasing also helps readers to pick up important notes once they're used to it.

Your code probably just was an example, but I think the summary needs emphasis least of all since it only notes – in a short sentence – what a type is or a method does. If anything, use it in the remarks and even then I'd carefully consider whether you actually need it.

There are other ways of adding emphasis:

 - Upper case:    some BOLD text       // you are shouting, but they WILL read it
 - First letter:  some Bold text       // less emphasis
 - Asterisks:     some **bold** text   // 2 asterisks seem to work best
 - Dashes:        some --bold-- text   // less emphasis

Plain text is old-school, but it can be very effective - and works long after the technology has changed.