diff --git a/app/vmselect/main.go b/app/vmselect/main.go
index af80bd413..a06e1ac35 100644
--- a/app/vmselect/main.go
+++ b/app/vmselect/main.go
@@ -468,7 +468,6 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 		return true
 	case "/metric-relabel-debug":
 		promscrapeMetricRelabelDebugRequests.Inc()
-		httpserver.EnableCORS(w, r)
 		promscrape.WriteMetricRelabelDebug(w, r)
 		return true
 	case "/target-relabel-debug":
diff --git a/app/vmselect/prometheus/expand-with-exprs.qtpl b/app/vmselect/prometheus/expand-with-exprs.qtpl
index 604f10fd0..d65393cb7 100644
--- a/app/vmselect/prometheus/expand-with-exprs.qtpl
+++ b/app/vmselect/prometheus/expand-with-exprs.qtpl
@@ -67,11 +67,11 @@ textarea { margin: 1em }
     {% code expr, err := metricsql.Parse(q) %}
     {% if err != nil %}
         "status": "error",
-        "error": {%q fmt.Sprintf("Cannot parse query: %s", err) %}
+        "error": {%q= fmt.Sprintf("Cannot parse query: %s", err) %}
     {% else %}
         {% code expr = metricsql.Optimize(expr) %}
         "status": "success",
-        "expr": {%qz expr.AppendString(nil) %}
+        "expr": {%qz= expr.AppendString(nil) %}
     {% endif %}
 }
 {% endfunc %}
diff --git a/app/vmselect/prometheus/expand-with-exprs.qtpl.go b/app/vmselect/prometheus/expand-with-exprs.qtpl.go
index 2fd45395b..ca91d957f 100644
--- a/app/vmselect/prometheus/expand-with-exprs.qtpl.go
+++ b/app/vmselect/prometheus/expand-with-exprs.qtpl.go
@@ -145,7 +145,7 @@ func StreamExpandWithExprsJSONResponse(qw422016 *qt422016.Writer, q string) {
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:68
 		qw422016.N().S(`"status": "error","error":`)
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:70
-		qw422016.E().Q(fmt.Sprintf("Cannot parse query: %s", err))
+		qw422016.N().Q(fmt.Sprintf("Cannot parse query: %s", err))
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:71
 	} else {
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:72
@@ -154,7 +154,7 @@ func StreamExpandWithExprsJSONResponse(qw422016 *qt422016.Writer, q string) {
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:72
 		qw422016.N().S(`"status": "success","expr":`)
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:74
-		qw422016.E().QZ(expr.AppendString(nil))
+		qw422016.N().QZ(expr.AppendString(nil))
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:75
 	}
 //line app/vmselect/prometheus/expand-with-exprs.qtpl:75
diff --git a/lib/promrelabel/debug.qtpl b/lib/promrelabel/debug.qtpl
index b015de0ff..0b612a165 100644
--- a/lib/promrelabel/debug.qtpl
+++ b/lib/promrelabel/debug.qtpl
@@ -138,33 +138,33 @@ function submitRelabelDebugForm(e) {
 {% endfunc %}
 
 {% func RelabelDebugStepsJSON(targetURL, targetID string, dss []DebugStep, metric, relabelConfigs string, err error) %}
-    {
-       {% if err != nil %}
-                "status": "error",
-                "error": {%q= fmt.Sprintf("Error: %s", err) %}
-        {% else %}
-                "status": "success",
-                {% if len(dss) > 0 %}
-                    "originalLabels": {%q= string(mustFormatLabels(dss[0].In)) %},
-                    "resultingLabels": {%q= string(mustFormatLabels(dss[len(dss)-1].Out)) %},
-                {% endif %}
-                "steps": [
-                    {% for i, ds := range dss %}
-                        {% code
-                            inLabels := promutils.MustNewLabelsFromString(ds.In)
-                            outLabels := promutils.MustNewLabelsFromString(ds.Out)
-                            changedLabels := getChangedLabelNames(inLabels, outLabels)
-                        %}
-                        {
-                            "inLabels": {%q= labelsWithHighlight(inLabels, changedLabels, "red") %},
-                            "outLabels": {%q= labelsWithHighlight(outLabels, changedLabels, "blue") %},
-                            "rule": {%q= ds.Rule %}
-                        }
-                        {% if i != len(dss)-1 %},{% endif %}
-                    {% endfor %}
-                ]
+{
+    {% if err != nil %}
+        "status": "error",
+        "error": {%q= fmt.Sprintf("Error: %s", err) %}
+    {% else %}
+        "status": "success",
+        {% if len(dss) > 0 %}
+            "originalLabels": {%q= mustFormatLabels(dss[0].In) %},
+            "resultingLabels": {%q= mustFormatLabels(dss[len(dss)-1].Out) %},
         {% endif %}
-    }
+        "steps": [
+            {% for i, ds := range dss %}
+                {% code
+                    inLabels := promutils.MustNewLabelsFromString(ds.In)
+                    outLabels := promutils.MustNewLabelsFromString(ds.Out)
+                    changedLabels := getChangedLabelNames(inLabels, outLabels)
+                %}
+                {
+                    "inLabels": {%q= labelsWithHighlight(inLabels, changedLabels, "red") %},
+                    "outLabels": {%q= labelsWithHighlight(outLabels, changedLabels, "blue") %},
+                    "rule": {%q= ds.Rule %}
+                }
+                {% if i != len(dss)-1 %},{% endif %}
+            {% endfor %}
+        ]
+    {% endif %}
+}
 {% endfunc %}
 
 {% func labelsWithHighlight(labels *promutils.Labels, highlight map[string]struct{}, color string) %}
diff --git a/lib/promrelabel/debug.qtpl.go b/lib/promrelabel/debug.qtpl.go
index fcca1f40b..40f29ec89 100644
--- a/lib/promrelabel/debug.qtpl.go
+++ b/lib/promrelabel/debug.qtpl.go
@@ -354,11 +354,11 @@ func StreamRelabelDebugStepsJSON(qw422016 *qt422016.Writer, targetURL, targetID
 //line lib/promrelabel/debug.qtpl:147
 			qw422016.N().S(`"originalLabels":`)
 //line lib/promrelabel/debug.qtpl:148
-			qw422016.N().Q(string(mustFormatLabels(dss[0].In)))
+			qw422016.N().Q(mustFormatLabels(dss[0].In))
 //line lib/promrelabel/debug.qtpl:148
 			qw422016.N().S(`,"resultingLabels":`)
 //line lib/promrelabel/debug.qtpl:149
-			qw422016.N().Q(string(mustFormatLabels(dss[len(dss)-1].Out)))
+			qw422016.N().Q(mustFormatLabels(dss[len(dss)-1].Out))
 //line lib/promrelabel/debug.qtpl:149
 			qw422016.N().S(`,`)
 //line lib/promrelabel/debug.qtpl:150
diff --git a/lib/promscrape/relabel_debug.go b/lib/promscrape/relabel_debug.go
index cc119a671..627bf68f6 100644
--- a/lib/promscrape/relabel_debug.go
+++ b/lib/promscrape/relabel_debug.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promrelabel"
 )
 
@@ -15,10 +16,6 @@ func WriteMetricRelabelDebug(w http.ResponseWriter, r *http.Request) {
 	format := r.FormValue("format")
 	var err error
 
-	if format == "json" {
-		w.Header().Set("Content-Type", "application/json")
-	}
-
 	if metric == "" && relabelConfigs == "" && targetID != "" {
 		pcs, labels, ok := getMetricRelabelContextByTargetID(targetID)
 		if !ok {
@@ -29,6 +26,10 @@ func WriteMetricRelabelDebug(w http.ResponseWriter, r *http.Request) {
 			relabelConfigs = pcs.String()
 		}
 	}
+	if format == "json" {
+		httpserver.EnableCORS(w, r)
+		w.Header().Set("Content-Type", "application/json")
+	}
 	promrelabel.WriteMetricRelabelDebug(w, targetID, metric, relabelConfigs, format, err)
 }
 
@@ -50,5 +51,9 @@ func WriteTargetRelabelDebug(w http.ResponseWriter, r *http.Request) {
 			relabelConfigs = pcs.String()
 		}
 	}
+	if format == "json" {
+		httpserver.EnableCORS(w, r)
+		w.Header().Set("Content-Type", "application/json")
+	}
 	promrelabel.WriteTargetRelabelDebug(w, targetID, metric, relabelConfigs, format, err)
 }