diff --git a/pipeline/outputs/gelf.md b/pipeline/outputs/gelf.md
index ee115ec10..d5a4c848e 100644
--- a/pipeline/outputs/gelf.md
+++ b/pipeline/outputs/gelf.md
@@ -14,6 +14,7 @@ According to [GELF Payload Specification](https://go2docs.graylog.org/5-0/gettin
 | Host                   | IP address or hostname of the target Graylog server                                                                                                                         | 127.0.0.1     |
 | Port                   | The port that your Graylog GELF input is listening on                                                                                                                       | 12201         |
 | Mode                   | The protocol to use (`tls`, `tcp` or `udp`)                                                                                                                                 | udp           |
+| Gelf\_Tag\_Key         | Key to be used for tag. (_Optional in GELF_)  |               |
 | Gelf_Short_Message_Key | A short descriptive message (**MUST be set in GELF**)                                                                                                                       | short_message |
 | Gelf_Timestamp_Key     | Your log timestamp (_SHOULD be set in GELF_)                                                                                                                                | timestamp     |
 | Gelf_Host_Key          | Key which its value is used as the name of the host, source or application that sent this message. (**MUST be set in GELF**)                                                | host          |