diff --git a/src/commands.cc b/src/commands.cc
index 46481b9d..6715fd05 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -1499,43 +1499,29 @@ const CommandDesc debug_cmd = {
             auto total = 0;
             write_to_debug_buffer("Memory usage:");
             const ColumnCount column_size = 17;
-            write_to_debug_buffer(format("{} │{} │{} │{} ",
-                                         left_pad("domain", column_size),
-                                         left_pad("bytes", column_size),
-                                         left_pad("active allocs", column_size),
-                                         left_pad("total allocs", column_size)));
+            write_to_debug_buffer(format("{:17} │{:17} │{:17} │{:17} ",
+                                         "domain",
+                                         "bytes",
+                                         "active allocs",
+                                         "total allocs"));
             write_to_debug_buffer(format("{0}┼{0}┼{0}┼{0}", String(Codepoint{0x2500}, column_size + 1)));
 
-            auto group = [](StringView s) {
-                String res;
-                auto pos = 0_byte, len = s.length();
-                if ((pos = len % 3) != 0)
-                    res += s.substr(0, pos);
-                for (; pos != len; pos += 3)
-                {
-                    if (not res.empty())
-                        res += ",";
-                    res += s.substr(pos, 3);
-                }
-                return res;
-            };
-
             for (int domain = 0; domain < (int)MemoryDomain::Count; ++domain)
             {
                 auto& stats = memory_stats[domain];
                 total += stats.allocated_bytes;
-                write_to_debug_buffer(format("{} │{} │{} │{} ",
-                                             left_pad(domain_name((MemoryDomain)domain), column_size),
-                                             left_pad(group(to_string(stats.allocated_bytes)), column_size),
-                                             left_pad(group(to_string(stats.allocation_count)), column_size),
-                                             left_pad(group(to_string(stats.total_allocation_count)), column_size)));
+                write_to_debug_buffer(format("{:17} │{:17} │{:17} │{:17} ",
+                                             domain_name((MemoryDomain)domain),
+                                             grouped(stats.allocated_bytes),
+                                             grouped(stats.allocation_count),
+                                             grouped(stats.total_allocation_count)));
             }
             write_to_debug_buffer({});
-            write_to_debug_buffer(format("  Total: {}", group(to_string(total))));
+            write_to_debug_buffer(format("  Total: {}", grouped(total)));
             #if defined(__GLIBC__) && (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 33))
-            write_to_debug_buffer(format("  Malloced: {}", group(to_string(mallinfo2().uordblks))));
+            write_to_debug_buffer(format("  Malloced: {}", grouped(mallinfo2().uordblks)));
             #elif defined(__GLIBC__) || defined(__CYGWIN__)
-            write_to_debug_buffer(format("  Malloced: {}", group(to_string(mallinfo().uordblks))));
+            write_to_debug_buffer(format("  Malloced: {}", grouped(mallinfo().uordblks)));
             #endif
         }
         else if (parser[0] == "shared-strings")
diff --git a/src/string_utils.cc b/src/string_utils.cc
index 39205d7e..f34bde03 100644
--- a/src/string_utils.cc
+++ b/src/string_utils.cc
@@ -195,6 +195,20 @@ InplaceString<23> to_string(Hex val)
     return to_string_impl<23>(val.val, 16);
 }
 
+InplaceString<23> to_string(Grouped val)
+{
+    auto ungrouped = to_string_impl<23>(val.val);
+
+    InplaceString<23> res;
+    for (int pos = 0, len = ungrouped.m_length; pos != len; ++pos)
+    {
+        if (res.m_length and ((len - pos) % 3) == 0) 
+            res.m_data[res.m_length++] = ',';
+        res.m_data[res.m_length++] = ungrouped.m_data[pos];
+    }
+    return res;
+}
+
 InplaceString<23> to_string(float val)
 {
 #if defined(__cpp_lib_to_chars)
@@ -338,12 +352,19 @@ void format_impl(StringView fmt, ArrayView<const StringView> params, AppendFunc
             if (closing == end)
                 throw runtime_error("format string error, unclosed '{'");
 
-            const int index = (closing == opening + 1) ?
-                implicitIndex : str_to_int({opening+1, closing});
+            auto format = std::find(opening+1, closing, ':');
+            const int index = opening+1 == format ? implicitIndex : str_to_int({opening+1, format});
 
             if (index >= params.size())
                 throw runtime_error("format string parameter index too big");
 
+            if (format != closing)
+            {
+                for (ColumnCount width = str_to_int({format+1, closing}), len = params[index].column_length();
+                     width > len; --width)
+                    append(' ');
+            }
+
             append(params[index]);
             implicitIndex = index+1;
             it = closing+1;
@@ -454,7 +475,7 @@ UnitTest test_string{[]()
     kak_assert(subsequence_match("tchou kanaky", "tchou kanaky"));
     kak_assert(not subsequence_match("tchou kanaky", "tchou  kanaky"));
 
-    kak_assert(format("Youhou {1} {} {0} \\{}", 10, "hehe", 5) == "Youhou hehe 5 10 {}");
+    kak_assert(format("Youhou {1} {} '{0:4}' \\{}", 10, "hehe", 5) == "Youhou hehe 5 '  10' {}");
 
     char buffer[20];
     kak_assert(format_to(buffer, "Hey {}", 15) == "Hey 15");
diff --git a/src/string_utils.hh b/src/string_utils.hh
index b2dc3d30..13d15018 100644
--- a/src/string_utils.hh
+++ b/src/string_utils.hh
@@ -117,19 +117,23 @@ struct InplaceString
     constexpr operator StringView() const { return {m_data, ByteCount{m_length}}; }
     operator String() const { return {m_data, ByteCount{m_length}}; }
 
-    unsigned char m_length;
+    unsigned char m_length{};
     char m_data[N];
 };
 
 struct Hex { size_t val; };
 constexpr Hex hex(size_t val) { return {val}; }
 
+struct Grouped { size_t val; };
+constexpr Grouped grouped(size_t val) { return {val}; }
+
 InplaceString<15> to_string(int val);
 InplaceString<15> to_string(unsigned val);
 InplaceString<23> to_string(long int val);
 InplaceString<23> to_string(unsigned long val);
 InplaceString<23> to_string(long long int val);
 InplaceString<23> to_string(Hex val);
+InplaceString<23> to_string(Grouped val);
 InplaceString<23> to_string(float val);
 InplaceString<7>  to_string(Codepoint c);