Where is this button?: "To search for pages and posts with a particular label or labels, use the Add a filter option at the bottom left of the page and choose Label."

[D Pozega]

This question is in reference to Atlassian Documentation: Confluence Search Syntax

I can find no such button.

[Cathy Rivard]

Just in case you're not sure where to look, the documentation is referring to the "Add a filter" link that appears at the bottom of the left menu on the Search Results page. This is an example from my instance (Cloud version):

Search - Label Filter Added.jpg

When you click "Add a filter", select "Label" from the list:

Search - Add a Filter.jpg

You can also refer to the main Search article: https://confluence.atlassian.com/doc/search-139528.html

[Milo Test]

This is certainly in Confluence Cloud, and if it isn't in Confluence Server 5.9, then it will be in a future version.

[D Pozega]

This appears to be it.  The workaround is using "labelTag:yourlabel" in the search box.

[Cathy Rivard]

I tried that syntax but it didn't work for me. I used "labelText:yourlabel" instead.

This article has all the fields you can search against this way: Confluence Search Fields

The filter I mentioned before is applied against search results. It's handy too!