diff --git a/main.go b/main.go
index ce425f8..4139a98 100644
--- a/main.go
+++ b/main.go
@@ -42,6 +42,9 @@ func root() *cobra.Command {
 			if err != nil {
 				return fmt.Errorf("parse coder URL: %w", err)
 			}
+			if parsedURL.Scheme != "http" && parsedURL.Scheme != "https" {
+				return fmt.Errorf("CODER_URL must include http:// or https:// scheme, got: %q", coderURL)
+			}
 
 			if len(kubeConfig) > 0 && kubeConfig[0] == '~' {
 				home, err := os.UserHomeDir()
diff --git a/main_test.go b/main_test.go
new file mode 100644
index 0000000..151cd56
--- /dev/null
+++ b/main_test.go
@@ -0,0 +1,50 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestRootCommand_URLValidation(t *testing.T) {
+	tests := []struct {
+		name      string
+		coderURL  string
+		wantError string
+	}{
+		{
+			name:      "missing scheme",
+			coderURL:  "coder.example.com",
+			wantError: "CODER_URL must include http:// or https:// scheme",
+		},
+		{
+			name:      "empty scheme with path",
+			coderURL:  "//coder.example.com",
+			wantError: "CODER_URL must include http:// or https:// scheme",
+		},
+		{
+			name:      "ftp scheme",
+			coderURL:  "ftp://coder.example.com",
+			wantError: "CODER_URL must include http:// or https:// scheme",
+		},
+		{
+			name:      "empty URL",
+			coderURL:  "",
+			wantError: "--coder-url is required",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cmd := root()
+			cmd.SetArgs([]string{"--coder-url", tt.coderURL})
+
+			err := cmd.Execute()
+
+			if err == nil {
+				t.Errorf("expected error containing %q, got nil", tt.wantError)
+			} else if !strings.Contains(err.Error(), tt.wantError) {
+				t.Errorf("expected error containing %q, got %q", tt.wantError, err.Error())
+			}
+		})
+	}
+}