diff --git a/src/matgl/cli.py b/src/matgl/cli.py
index 79ea51fe..3fb551ca 100644
--- a/src/matgl/cli.py
+++ b/src/matgl/cli.py
@@ -57,7 +57,7 @@ def relax_structure(args):
             print("Sites (Fractional coordinates)")
 
             def fmt_fcoords(fc):
-                return np.array2string(fc, formatter={"float_kind": lambda x: "%.5f" % x})
+                return np.array2string(fc, formatter={"float_kind": lambda x: f"{x:.5f}"})
 
             for old_site, new_site in zip(structure, final_structure):
                 print(f"{old_site.species}: {fmt_fcoords(old_site.frac_coords)} -> {fmt_fcoords(new_site.frac_coords)}")