diff --git a/internal/cli/validate.go b/internal/cli/validate.go
index 1adfee5..6f3a623 100644
--- a/internal/cli/validate.go
+++ b/internal/cli/validate.go
@@ -11,16 +11,19 @@ import (
 // NewValidateCmd creates the "burnless validate" command.
 func NewValidateCmd() *cobra.Command {
 	return &cobra.Command{
-		Use:          "validate <file>",
+		Use:          "validate [file]",
 		Short:        "Validate an sre.yaml file",
-		Args:         cobra.ExactArgs(1),
+		Args:         cobra.MaximumNArgs(1),
 		SilenceUsage: true,
 		RunE:         runValidate,
 	}
 }
 
 func runValidate(cmd *cobra.Command, args []string) error {
-	path := args[0]
+	path := "sre.yaml"
+	if len(args) > 0 {
+		path = args[0]
+	}
 
 	cfg, err := config.Load(path)
 	if err != nil {
diff --git a/internal/cli/validate_test.go b/internal/cli/validate_test.go
index 12f8ff2..cdd7d39 100644
--- a/internal/cli/validate_test.go
+++ b/internal/cli/validate_test.go
@@ -51,3 +51,32 @@ func TestRunValidate_MissingFile(t *testing.T) {
 		t.Fatal("expected error for missing file, got nil")
 	}
 }
+
+func TestRunValidate_DefaultFile(t *testing.T) {
+	// change to a temp dir with a valid sre.yaml
+	tmp := t.TempDir()
+	sre := `
+service: payments-api
+slos:
+  - name: availability
+    target: 99.9
+    window: 30d
+`
+	if err := os.WriteFile(filepath.Join(tmp, "sre.yaml"), []byte(sre), 0o644); err != nil {
+		t.Fatalf("failed to write sre.yaml: %v", err)
+	}
+
+	// change working directory to temp dir
+	orig, _ := os.Getwd()
+	defer func() { _ = os.Chdir(orig) }()
+	if err := os.Chdir(tmp); err != nil {
+		t.Fatalf("failed to chdir: %v", err)
+	}
+
+	// run validate with NO arguments — should find sre.yaml automatically
+	cmd := NewValidateCmd()
+	cmd.SetArgs([]string{})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("expected no error with default sre.yaml, got: %v", err)
+	}
+}