+ * This script listiner which should be configured on the issue updated event shows how you can have a field to calculate and show the number of labels on an issue. 

+ * "All right, title and interest in this code snippet shall remain the exclusive intellectual property of Adaptavist Group Ltd and its affiliates. Customers with a valid ScriptRunner 

+ * license shall be granted a  non-exclusive, non-transferable, freely revocable right to use this code snippet only within their own instance of Atlassian products. This licensing notice cannot be removed

+ * or amended and must be included in any circumstances where the code snippet is shared by You or a third party." 

+ */

+

+def customFields = get("/rest/api/2/field")

+        .asObject(List)

+        .body

+        .findAll { (it as Map).custom } as List<Map>

+

+// Specify the Name of the custom type field that will out the calcuated value

+def outputCfId = customFields.find { it.name == '<NumberFieldNameHere>' }?.id

+

+// Specify the project where the calculated field will go

+def projectKey = "<ProjectKeyHere>"

+

+if (issue == null || ((Map)issue.fields.project).key != projectKey) {

+    logger.info("Wrong Project \${issue.fields.project.key}")

+    return

+}

+

+// store the number of labels

+def NumberofLabels =  (issue.fields.labels.size)

+int output = NumberofLabels.toInteger()

+

+if (output == (issue.fields[outputCfId] as Integer)) {

+    logger.info("already been updated")

+    return

+}

+

+// Update the issue with the calculated value

+put("/rest/api/2/issue/${issue.key}")

+        .header("Content-Type", "application/json")

+        .body([

+        fields:[

+                (outputCfId): output

+        ]

+])