Microsoft has some documentation here: Code Search Results - Fetch Code Search Results
However, for the "filters" in the "Request Body" section, the only thing mentioned is: "filters object Filters to be applied. Set it to null if there are no filters to be applied."
There is an example that includes some filters, but there must be a comprehensive list of available filters somewhere. Is there documentation somewhere on filters? Or access to the CodeSearch marketplace installable source code to check to see what is supported (I checked GitHub, but no luck - the PowerShell/SQL admin scripts are there, but could not find anything else)?
Specifically, I would like to know if there is a "Tag" or "Tags" filter available. Testing in Postman indicates that there is no "Tag" filter. But there is a "Branch" filter, but no "Tag" filter. Git implements branches with "refs" - likewise, Git implements tags with "refs". Therefore, it should be simple to support a "Tag" filter in the Code Search API - since this support exists for the "Branch" filter. (I have tested with Postman and can confirm that the "Branch" filter works, but no permutation of "Tag" is supported)
Used Postman to POST to the Azure DevOps REST API for codesearchresults with the payload containing the "filters" for a valid "Branch" name. This works as advertised, but using a filter name of "Tag" or "Tags" or "[Tt]ag" returns an error: "message": "Unknown filter [Tag] found."
The tag/tags filter is not supported on Code Search, and it also is not supported even when manually doing the Code Search on the web UI of Azure DevOps.
If your projects really need this feature, I recommend you try to report a feature request on Developer Community. This will make it more convenient for the engineer teams to receive and understand your ideas. And your feedback also could be helpful for improving the Azure DevOps products.