ZTag is a utility that works in conjunction with ZMap and ZGrab and allows annotating raw scan data with additional metadata (e.g., device models and vulnerabilities) and transforming records. ZTag is used extensively within Censys (https://www.censys.io) to produce the data present in the search engine. However, it can also be run independently with ZMap and ZGrab.
ZTag consumes the JSON output from ZGrab scanner and then produces its own JSON output. Most simply, these JSON documents can be piped into ztag. For example, when processing an HTTP ZGrab Scan:
cat http.json | ztag -p 80 -P http -S get
There is a long list of protocol/subprotocol combinations that exist but are not particularly well documented.