diff --git a/internal/exporter/html.go b/internal/exporter/html.go
index 752aee9..292ed2e 100644
--- a/internal/exporter/html.go
+++ b/internal/exporter/html.go
@@ -1,7 +1,6 @@
 package exporter
 
 import (
-	"encoding/json"
 	"fmt"
 	"html"
 	"html/template"
@@ -18,7 +17,6 @@ type htmlData struct {
 	Format     string
 	Iterations []htmlIteration
 	Summary    htmlSummary
-	DataJSON   template.JS
 }
 
 type htmlIteration struct {
@@ -117,9 +115,6 @@ func buildHTMLData(t *trace.Trace) htmlData {
 		}
 	}
 
-	jsonBytes, _ := json.Marshal(d.Iterations)
-	d.DataJSON = template.JS(string(jsonBytes))
-
 	return d
 }
 
diff --git a/internal/exporter/html_test.go b/internal/exporter/html_test.go
new file mode 100644
index 0000000..ac6f2d3
--- /dev/null
+++ b/internal/exporter/html_test.go
@@ -0,0 +1,82 @@
+package exporter
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/loop-eng/looprelay/internal/trace"
+)
+
+func TestExportHTML_NoDeadDataJSON(t *testing.T) {
+	tr := trace.New([]trace.Iteration{
+		{
+			Number:  1,
+			Phase:   trace.PhaseAct,
+			Action:  trace.Action{Type: "Edit", Target: "main.go", Diff: "+package main\n"},
+			Tokens:  trace.TokenUsage{InputTokens: 10, OutputTokens: 5},
+			Context: trace.ContextState{FillPct: 42, Compactions: 1},
+			CostUSD: 0.01,
+		},
+		{
+			Number:       2,
+			Phase:        trace.PhaseVerify,
+			Verification: &trace.Verification{Status: "success", Output: "ok"},
+			Tokens:       trace.TokenUsage{InputTokens: 8, OutputTokens: 2},
+			CostUSD:      0.005,
+		},
+	})
+	tr.SourceFile = "demo.ltf"
+	tr.SourceFormat = "ltf"
+	tr.SessionID = "sess-1"
+	tr.Agent = "claude"
+
+	out := filepath.Join(t.TempDir(), "replay.html")
+	if err := ExportHTML(tr, out); err != nil {
+		t.Fatalf("ExportHTML: %v", err)
+	}
+
+	raw, err := os.ReadFile(out)
+	if err != nil {
+		t.Fatalf("read output: %v", err)
+	}
+	html := string(raw)
+
+	if !strings.Contains(html, "Iteration 1") {
+		t.Error("expected iteration 1 in HTML")
+	}
+	if !strings.Contains(html, "Iteration 2") {
+		t.Error("expected iteration 2 in HTML")
+	}
+	if !strings.Contains(html, `const total = 2`) {
+		t.Error("expected JS total from summary")
+	}
+	// Regression: unused DataJSON must not be reintroduced into the page.
+	if strings.Contains(html, "DataJSON") {
+		t.Error("HTML must not reference unused DataJSON")
+	}
+	// Marshal of iterations used to inject a raw JSON blob into the page; ensure gone.
+	if strings.Contains(html, `"ActionType"`) || strings.Contains(html, `"PhaseClass"`) {
+		t.Error("HTML must not embed marshaled htmlIteration JSON (former DataJSON)")
+	}
+}
+
+func TestBuildHTMLData_OmitsDataJSONComputation(t *testing.T) {
+	tr := trace.New([]trace.Iteration{
+		{Number: 1, Phase: trace.PhasePlan, CostUSD: 0.02},
+	})
+	tr.SourceFile = "x.ltf"
+	tr.SourceFormat = "ltf"
+
+	d := buildHTMLData(tr)
+	if len(d.Iterations) != 1 {
+		t.Fatalf("expected 1 iteration, got %d", len(d.Iterations))
+	}
+	if d.Iterations[0].Phase != "plan" {
+		t.Errorf("expected plan phase, got %q", d.Iterations[0].Phase)
+	}
+	if d.Summary.TotalIterations != 1 {
+		t.Errorf("expected summary total 1, got %d", d.Summary.TotalIterations)
+	}
+}