diff --git a/pkg/inventory/badge.go b/pkg/inventory/badge.go
new file mode 100644
index 0000000..d039330
--- /dev/null
+++ b/pkg/inventory/badge.go
@@ -0,0 +1,51 @@
+package inventory
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+)
+
+// StockReader abstracts the inventory getter for badge rendering.
+type StockReader interface {
+	GetInventory(ctx context.Context, sku SKU, locationID LocationID) (int64, error)
+}
+
+// BadgeHandler returns an http.HandlerFunc that renders an HTML stock badge fragment.
+func BadgeHandler(reader StockReader) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		sku := r.URL.Query().Get("sku")
+		if sku == "" {
+			http.Error(w, "missing sku parameter", http.StatusBadRequest)
+			return
+		}
+
+		locationID := LocationID(r.URL.Query().Get("location_id"))
+		if locationID == "" {
+			locationID = "default"
+		}
+
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Header().Set("Cache-Control", "private, max-age=5")
+
+		qty, err := reader.GetInventory(r.Context(), SKU(sku), locationID)
+		if err != nil {
+			w.WriteHeader(http.StatusOK)
+			w.Write([]byte(`<span class="stock-badge stock-unknown" data-sku="` + sku + `">Availability unavailable</span>`))
+			return
+		}
+
+		var htmlSnippet string
+		switch {
+		case qty > 10:
+			htmlSnippet = fmt.Sprintf(`<span class="stock-badge stock-in-stock" data-sku="%s">✓ In stock</span>`, sku)
+		case qty > 0:
+			htmlSnippet = fmt.Sprintf(`<span class="stock-badge stock-low-stock" data-sku="%s">⚡ Only %d left!</span>`, sku, qty)
+		default:
+			htmlSnippet = fmt.Sprintf(`<span class="stock-badge stock-out-of-stock" data-sku="%s">✕ Out of stock</span>`, sku)
+		}
+
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(htmlSnippet))
+	}
+}
diff --git a/pkg/inventory/badge_test.go b/pkg/inventory/badge_test.go
new file mode 100644
index 0000000..b5fbad6
--- /dev/null
+++ b/pkg/inventory/badge_test.go
@@ -0,0 +1,94 @@
+package inventory
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+type mockStockReader struct {
+	stock map[string]int64
+	err   error
+}
+
+func (m *mockStockReader) GetInventory(ctx context.Context, sku SKU, locationID LocationID) (int64, error) {
+	if m.err != nil {
+		return 0, m.err
+	}
+	qty, ok := m.stock[string(sku)]
+	if !ok {
+		return 0, errors.New("sku not found")
+	}
+	return qty, nil
+}
+
+func TestBadgeHandler(t *testing.T) {
+	mock := &mockStockReader{
+		stock: map[string]int64{
+			"HIGH": 25,
+			"LOW":  3,
+			"OUT":  0,
+		},
+	}
+
+	handler := BadgeHandler(mock)
+
+	tests := []struct {
+		name           string
+		url            string
+		expectedCode   int
+		expectedSubstr string
+	}{
+		{
+			name:           "missing sku",
+			url:            "/inventory/badge",
+			expectedCode:   http.StatusBadRequest,
+			expectedSubstr: "missing sku parameter",
+		},
+		{
+			name:           "high stock",
+			url:            "/inventory/badge?sku=HIGH",
+			expectedCode:   http.StatusOK,
+			expectedSubstr: "stock-in-stock",
+		},
+		{
+			name:           "low stock",
+			url:            "/inventory/badge?sku=LOW",
+			expectedCode:   http.StatusOK,
+			expectedSubstr: "Only 3 left!",
+		},
+		{
+			name:           "out of stock",
+			url:            "/inventory/badge?sku=OUT",
+			expectedCode:   http.StatusOK,
+			expectedSubstr: "stock-out-of-stock",
+		},
+		{
+			name:           "unknown stock / error",
+			url:            "/inventory/badge?sku=UNKNOWN",
+			expectedCode:   http.StatusOK,
+			expectedSubstr: "stock-unknown",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodGet, tt.url, nil)
+			rr := httptest.NewRecorder()
+
+			handler.ServeHTTP(rr, req)
+
+			if rr.Code != tt.expectedCode {
+				t.Errorf("expected status code %d, got %d", tt.expectedCode, rr.Code)
+			}
+
+			body := rr.Body.String()
+			if !strings.Contains(body, tt.expectedSubstr) {
+				t.Errorf("expected body to contain %q, got %q", tt.expectedSubstr, body)
+			}
+		})
+	}
+}