diff --git a/cmd/mt-index-cat/main.go b/cmd/mt-index-cat/main.go
index 8076b0e4e2..e46a35eba7 100644
--- a/cmd/mt-index-cat/main.go
+++ b/cmd/mt-index-cat/main.go
@@ -26,6 +26,7 @@ func main() {
 	var addr string
 	var prefix string
 	var substr string
+	var tags string
 	var from string
 	var maxAge string
 	var verbose bool
@@ -35,6 +36,7 @@ func main() {
 	globalFlags.StringVar(&addr, "addr", "http://localhost:6060", "graphite/metrictank address")
 	globalFlags.StringVar(&prefix, "prefix", "", "only show metrics that have this prefix")
 	globalFlags.StringVar(&substr, "substr", "", "only show metrics that have this substring")
+	globalFlags.StringVar(&tags, "tags", "", "tag filter. empty (default), 'some', 'none', 'valid', or 'invalid'")
 	globalFlags.StringVar(&from, "from", "30min", "for vegeta outputs, will generate requests for data starting from now minus... eg '30min', '5h', '14d', etc. or a unix timestamp")
 	globalFlags.StringVar(&maxAge, "max-age", "6h30min", "max age (last update diff with now) of metricdefs.  use 0 to disable")
 	globalFlags.IntVar(&limit, "limit", 0, "only show this many metrics.  use 0 to disable")
@@ -55,6 +57,13 @@ func main() {
 		fmt.Printf("global config flags:\n\n")
 		globalFlags.PrintDefaults()
 		fmt.Println()
+		fmt.Println("tags filter:")
+		fmt.Println("     ''        no filtering based on tags")
+		fmt.Println("     'none'    only show metrics that have no tags")
+		fmt.Println("     'some'    only show metrics that have one or more tags")
+		fmt.Println("     'valid'   only show metrics whose tags (if any) are valid")
+		fmt.Println("     'invalid' only show metrics that have one or more invalid tags")
+		fmt.Println()
 		fmt.Printf("idxtype: only 'cass' supported for now\n\n")
 		fmt.Printf("cass config flags:\n\n")
 		cassFlags.PrintDefaults()
@@ -111,6 +120,12 @@ func main() {
 		os.Exit(1)
 	}
 
+	if tags != "" && tags != "valid" && tags != "invalid" && tags != "some" && tags != "none" {
+		log.Println("invalid tags filter")
+		flag.Usage()
+		os.Exit(1)
+	}
+
 	globalFlags.Parse(os.Args[1:cassI])
 	cassFlags.Parse(os.Args[cassI+1 : len(os.Args)-1])
 	cassandra.Enabled = true
@@ -155,15 +170,33 @@ func main() {
 	shown := 0
 
 	for _, d := range defs {
-		if prefix == "" || strings.HasPrefix(d.Metric, prefix) {
-			if substr == "" || strings.Contains(d.Metric, substr) {
-				show(d)
-				shown += 1
-				if shown == limit {
-					break
-				}
+		// note that prefix and substr can be "", meaning filter disabled.
+		// the conditions handle this fine as well.
+		if !strings.HasPrefix(d.Metric, prefix) {
+			continue
+		}
+		if !strings.Contains(d.Metric, substr) {
+			continue
+		}
+		if tags == "none" && len(d.Tags) != 0 {
+			continue
+		}
+		if tags == "some" && len(d.Tags) == 0 {
+			continue
+		}
+		if tags == "valid" || tags == "invalid" {
+			valid := schema.ValidateTags(d.Tags)
+
+			// skip the metric if the validation result is not what we want
+			if valid != (tags == "valid") {
+				continue
 			}
 		}
+		show(d)
+		shown += 1
+		if shown == limit {
+			break
+		}
 	}
 
 	if verbose {
diff --git a/docs/tools.md b/docs/tools.md
index 9b368cd6f9..d25713b445 100644
--- a/docs/tools.md
+++ b/docs/tools.md
@@ -70,9 +70,18 @@ global config flags:
     	only show metrics that have this prefix
   -substr string
     	only show metrics that have this substring
+  -tags string
+    	tag filter. empty (default), 'some', 'none', 'valid', or 'invalid'
   -verbose
     	print stats to stderr
 
+tags filter:
+     ''        no filtering based on tags
+     'none'    only show metrics that have no tags
+     'some'    only show metrics that have one or more tags
+     'valid'   only show metrics whose tags (if any) are valid
+     'invalid' only show metrics that have one or more invalid tags
+
 idxtype: only 'cass' supported for now
 
 cass config flags:
diff --git a/vendor/gopkg.in/raintank/schema.v1/metric.go b/vendor/gopkg.in/raintank/schema.v1/metric.go
index 1de6dd1d1f..e00403b1a2 100644
--- a/vendor/gopkg.in/raintank/schema.v1/metric.go
+++ b/vendor/gopkg.in/raintank/schema.v1/metric.go
@@ -62,7 +62,7 @@ func (m *MetricData) Validate() error {
 	if m.Mtype == "" || (m.Mtype != "gauge" && m.Mtype != "rate" && m.Mtype != "count" && m.Mtype != "counter" && m.Mtype != "timestamp") {
 		return errInvalidMtype
 	}
-	if !validateTags(m.Tags) {
+	if !ValidateTags(m.Tags) {
 		return errInvalidTagFormat
 	}
 	return nil
@@ -208,7 +208,7 @@ func (m *MetricDefinition) Validate() error {
 	if m.Mtype == "" || (m.Mtype != "gauge" && m.Mtype != "rate" && m.Mtype != "count" && m.Mtype != "counter" && m.Mtype != "timestamp") {
 		return errInvalidMtype
 	}
-	if !validateTags(m.Tags) {
+	if !ValidateTags(m.Tags) {
 		return errInvalidTagFormat
 	}
 	return nil
@@ -263,36 +263,33 @@ func MetricDefinitionFromMetricData(d *MetricData) *MetricDefinition {
 	return md
 }
 
-// validateTags verifies that all the tags are of a valid format. If one or more
-// are invalid it returns false, otherwise true.
-// a valid format is anything that looks like key=value, the length of key and
-// value must be >0 and both must not contain the ; character.
-func validateTags(tags []string) bool {
+// ValidateTags returns whether all tags are in a valid format.
+// a valid format is anything that looks like key=value,
+// the length of key and value must be >0 and both must not contain the ; character.
+func ValidateTags(tags []string) bool {
 	for _, t := range tags {
 		if len(t) == 0 {
 			return false
 		}
 
-		// any = must not be the first character
-		if t[0] == 61 {
+		if t[0] == '=' {
 			return false
 		}
 
 		foundEqual := false
 		for pos := 0; pos < len(t); pos++ {
-			// no ; allowed
-			if t[pos] == 59 {
+			if t[pos] == ';' {
 				return false
 			}
 
 			if !foundEqual {
 				// no ! allowed in key
-				if t[pos] == 33 {
+				if t[pos] == '!' {
 					return false
 				}
 
 				// found the first =, so this will be the separator between key & value
-				if t[pos] == 61 {
+				if t[pos] == '=' {
 					// first equal sign must not be the last character
 					if pos == len(t)-1 {
 						return false