Which search syntax restricts an "alert" tag to the "host" field?

The syntax that restricts an "alert" tag specifically to the "host" field is represented correctly in the selections provided as 'tag::host=alert'. This format uses the double colon operator, which denotes that the tag is being filtered down to a specific field—in this case, the "host" field.

Using this search syntax allows you to focus the retrieval of events that are both marked with the 'alert' tag and belong to the specified "host". It effectively narrows down the results to those that are relevant to both conditions, making your searches more precise and efficient in Splunk.

The other options would not serve to restrict the tag to the host field in the same way. For instance, simply using 'tag=alert' without the field specification would retrieve all events that have the 'alert' tag across all hosts, which might not be what you want if you're looking for data from a specific host. Similarly, variations with confusing punctuation or incorrect syntax, like those that include 'host::tag::alert' or 'tag==alert,' do not adhere to the correct search command syntax used in Splunk and would either produce errors or yield broader, unintended results.