diff --git a/.gitignore b/.gitignore
index b1a41919..4c2a2bf8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,5 @@
 # Auto generated files
-build/*
+build/*
 *.slo
 *.lo
 *.o
@@ -65,4 +65,7 @@ install_manifest.txt
 /tests/logs/*
 
 # idea
-.idea/
\ No newline at end of file
+.idea/
+
+# vscode
+.vscode/
diff --git a/include/spdlog/common.h b/include/spdlog/common.h
index dd9a4785..335975e6 100644
--- a/include/spdlog/common.h
+++ b/include/spdlog/common.h
@@ -80,6 +80,7 @@ using log_clock = std::chrono::system_clock;
 using sink_ptr = std::shared_ptr<sinks::sink>;
 using sinks_init_list = std::initializer_list<sink_ptr>;
 using log_err_handler = std::function<void(const std::string &err_msg)>;
+using log_custom_flags = std::unordered_map<char, std::string>;
 
 // string_view type - either std::string_view or fmt::string_view (pre c++17)
 #if defined(FMT_USE_STD_STRING_VIEW)
diff --git a/include/spdlog/details/log_msg.h b/include/spdlog/details/log_msg.h
index 69422ba3..53cd1a7d 100644
--- a/include/spdlog/details/log_msg.h
+++ b/include/spdlog/details/log_msg.h
@@ -10,15 +10,17 @@
 
 #include <string>
 #include <utility>
+#include <unordered_map>
 
 namespace spdlog {
 namespace details {
 struct log_msg
 {
 
-    log_msg(source_loc loc, const std::string *loggers_name, level::level_enum lvl, string_view_t view)
+    log_msg(source_loc loc, const std::string *loggers_name, level::level_enum lvl, const log_custom_flags *flags, string_view_t view)
         : logger_name(loggers_name)
         , level(lvl)
+        , custom_flags(flags)
 #ifndef SPDLOG_NO_DATETIME
         , time(os::now())
 #endif
@@ -31,8 +33,8 @@ struct log_msg
     {
     }
 
-    log_msg(const std::string *loggers_name, level::level_enum lvl, string_view_t view)
-        : log_msg(source_loc{}, loggers_name, lvl, view)
+    log_msg(const std::string *loggers_name, level::level_enum lvl, const log_custom_flags *flags, string_view_t view)
+        : log_msg(source_loc{}, loggers_name, lvl, flags, view)
     {
     }
 
@@ -40,6 +42,7 @@ struct log_msg
 
     const std::string *logger_name{nullptr};
     level::level_enum level{level::off};
+    const spdlog::log_custom_flags *custom_flags{nullptr};
     log_clock::time_point time;
     size_t thread_id{0};
     size_t msg_id{0};
diff --git a/include/spdlog/details/logger_impl.h b/include/spdlog/details/logger_impl.h
index d44652b5..9dbbd580 100644
--- a/include/spdlog/details/logger_impl.h
+++ b/include/spdlog/details/logger_impl.h
@@ -70,8 +70,9 @@ inline void spdlog::logger::log(source_loc source, level::level_enum lvl, const
         using details::fmt_helper::to_string_view;
         fmt::memory_buffer buf;
         fmt::format_to(buf, fmt, args...);
-        details::log_msg log_msg(source, &name_, lvl, to_string_view(buf));
+        details::log_msg log_msg(source, &name_, lvl, &custom_flags_, to_string_view(buf));
         sink_it_(log_msg);
+
     }
     SPDLOG_CATCH_AND_HANDLE
 }
@@ -91,7 +92,7 @@ inline void spdlog::logger::log(source_loc source, level::level_enum lvl, const
 
     try
     {
-        details::log_msg log_msg(source, &name_, lvl, spdlog::string_view_t(msg));
+        details::log_msg log_msg(source, &name_, lvl, &custom_flags_, spdlog::string_view_t(msg));
         sink_it_(log_msg);
     }
     SPDLOG_CATCH_AND_HANDLE
@@ -117,7 +118,7 @@ inline void spdlog::logger::log(source_loc source, level::level_enum lvl, const
     }
     try
     {
-        details::log_msg log_msg(source, &name_, lvl, msg);
+        details::log_msg log_msg(source, &name_, lvl, &custom_flags_, msg);
         sink_it_(log_msg);
     }
     SPDLOG_CATCH_AND_HANDLE
@@ -135,7 +136,7 @@ inline void spdlog::logger::log(source_loc source, level::level_enum lvl, const
         using details::fmt_helper::to_string_view;
         fmt::memory_buffer buf;
         fmt::format_to(buf, "{}", msg);
-        details::log_msg log_msg(source, &name_, lvl, to_string_view(buf));
+        details::log_msg log_msg(source, &name_, lvl, &custom_flags_, to_string_view(buf));
         sink_it_(log_msg);
     }
     SPDLOG_CATCH_AND_HANDLE
@@ -252,7 +253,7 @@ inline void spdlog::logger::log(source_loc source, level::level_enum lvl, const
         fmt::format_to(wbuf, fmt, args...);
         fmt::memory_buffer buf;
         wbuf_to_utf8buf(wbuf, buf);
-        details::log_msg log_msg(source, &name_, lvl, to_string_view(buf));
+        details::log_msg log_msg(source, &name_, lvl, &custom_flags_, to_string_view(buf));
         sink_it_(log_msg);
     }
     SPDLOG_CATCH_AND_HANDLE
@@ -315,6 +316,30 @@ inline void spdlog::logger::set_level(spdlog::level::level_enum log_level)
     level_.store(log_level);
 }
 
+inline void spdlog::logger::set_custom_flag(char flag, const std::string& value)
+{
+    custom_flags_[flag] = value;
+}
+
+inline const std::string& spdlog::logger::get_custom_flag(char flag) const
+{
+    auto it = custom_flags_.find(flag);
+    if (it != custom_flags_.end())
+    {
+        return it->second;
+    }
+    else
+    {
+        static std::string empty;
+        return empty;
+    }
+}
+
+inline const spdlog::log_custom_flags &spdlog::logger::custom_flags() const
+{
+    return custom_flags_;
+}
+
 inline void spdlog::logger::set_error_handler(spdlog::log_err_handler err_handler)
 {
     err_handler_ = std::move(err_handler);
diff --git a/include/spdlog/details/pattern_formatter.h b/include/spdlog/details/pattern_formatter.h
index c0ad86e8..39bca48b 100644
--- a/include/spdlog/details/pattern_formatter.h
+++ b/include/spdlog/details/pattern_formatter.h
@@ -777,6 +777,38 @@ private:
     char ch_;
 };
 
+class custom_formatter final : public flag_formatter
+{
+public:
+    explicit custom_formatter(padding_info padinfo, char flag)
+        : flag_formatter(padinfo), flag_(flag){};
+
+    void format(const details::log_msg &msg, const std::tm &, fmt::memory_buffer &dest) override
+    {
+        auto it = msg.custom_flags->find(flag_);
+        if (it != msg.custom_flags->end())
+        {
+            if (padinfo_.enabled())
+            {
+                scoped_pad p(it->second.size(), padinfo_, dest);
+                fmt_helper::append_string_view(it->second, dest);
+            }
+            else
+            {
+                fmt_helper::append_string_view(it->second, dest);
+            }
+        }
+        else
+        {
+            dest.push_back('%');
+            dest.push_back(flag_);
+        }
+    }
+
+private:
+    char flag_;
+};
+
 // aggregate user chars to display as is
 class aggregate_formatter final : public flag_formatter
 {
@@ -1241,11 +1273,8 @@ private:
             formatters_.push_back(details::make_unique<details::ch_formatter>('%'));
             break;
 
-        default: // Unknown flag appears as is
-            auto unknown_flag = details::make_unique<details::aggregate_formatter>();
-            unknown_flag->add_ch('%');
-            unknown_flag->add_ch(flag);
-            formatters_.push_back((std::move(unknown_flag)));
+        default: // Unknown flag is either a custom flag or appears as is
+            formatters_.push_back(details::make_unique<details::custom_formatter>(padding, flag));
             break;
         }
     }
diff --git a/include/spdlog/details/registry.h b/include/spdlog/details/registry.h
index ccd53955..1abaf332 100644
--- a/include/spdlog/details/registry.h
+++ b/include/spdlog/details/registry.h
@@ -198,6 +198,28 @@ public:
         default_logger_.reset();
     }
 
+    void set_custom_flag(char flag, const std::string& value)
+    {
+        std::lock_guard<std::mutex> lock(logger_map_mutex_);
+        for (auto& l : loggers_)
+            l.second->set_custom_flag(flag, value);
+        custom_flags_[flag] = value;
+    }
+
+    const std::string& get_custom_flag(char flag)
+    {
+        auto it = custom_flags_.find(flag);
+        if (it != custom_flags_.end())
+        {
+            return it->second;
+        }
+        else
+        {
+            static std::string empty;
+            return empty;
+        }
+    }
+
     // clean all resources and threads started by the registry
     void shutdown()
     {
@@ -279,6 +301,7 @@ private:
     std::unique_ptr<periodic_worker> periodic_flusher_;
     std::shared_ptr<logger> default_logger_;
     bool automatic_registration_ = true;
+    spdlog::log_custom_flags custom_flags_;
 };
 
 } // namespace details
diff --git a/include/spdlog/details/thread_pool.h b/include/spdlog/details/thread_pool.h
index 35578971..2d747a86 100644
--- a/include/spdlog/details/thread_pool.h
+++ b/include/spdlog/details/thread_pool.h
@@ -104,7 +104,7 @@ struct async_msg
     // copy into log_msg
     log_msg to_log_msg()
     {
-        log_msg msg(&worker_ptr->name(), level, string_view_t(raw.data(), raw.size()));
+        log_msg msg(&worker_ptr->name(), level, &worker_ptr->custom_flags(), string_view_t(raw.data(), raw.size()));
         msg.time = time;
         msg.thread_id = thread_id;
         msg.msg_id = msg_id;
diff --git a/include/spdlog/logger.h b/include/spdlog/logger.h
index ec06828f..ce028074 100644
--- a/include/spdlog/logger.h
+++ b/include/spdlog/logger.h
@@ -1,5 +1,5 @@
 //
-// Copyright(c) 2015-2108 Gabi Melman.
+// Copyright(c) 2015-2019 Gabi Melman.
 // Distributed under the MIT License (http://opensource.org/licenses/MIT)
 //
 
@@ -24,6 +24,7 @@
 
 #include <memory>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 namespace spdlog {
@@ -133,6 +134,11 @@ public:
     void set_level(level::level_enum log_level);
 
     static level::level_enum default_level();
+
+    void set_custom_flag(char flag, const std::string& value);
+    const std::string &get_custom_flag(char flag) const;
+    const log_custom_flags &custom_flags() const;
+
     level::level_enum level() const;
     const std::string &name() const;
 
@@ -177,6 +183,7 @@ protected:
     log_err_handler err_handler_{[this](const std::string &msg) { this->default_err_handler_(msg); }};
     std::atomic<time_t> last_err_time_{0};
     std::atomic<size_t> msg_counter_{1};
+    log_custom_flags custom_flags_;
 };
 } // namespace spdlog
 
diff --git a/include/spdlog/spdlog.h b/include/spdlog/spdlog.h
index 20ff24be..e5280cb4 100644
--- a/include/spdlog/spdlog.h
+++ b/include/spdlog/spdlog.h
@@ -99,6 +99,18 @@ inline void register_logger(std::shared_ptr<logger> logger)
     details::registry::instance().register_logger(std::move(logger));
 }
 
+// Set custom flag
+inline void set_custom_flag(char flag, const std::string value)
+{
+    details::registry::instance().set_custom_flag(flag, std::move(value));
+}
+
+// Get custom flag
+inline const std::string &get_custom_flag(char flag)
+{
+    return details::registry::instance().get_custom_flag(flag);
+}
+
 // Apply a user defined function on all registered loggers
 // Example:
 // spdlog::apply_all([&](std::shared_ptr<spdlog::logger> l) {l->flush();});
diff --git a/tests/test_pattern_formatter.cpp b/tests/test_pattern_formatter.cpp
index fb6f75da..8e66413f 100644
--- a/tests/test_pattern_formatter.cpp
+++ b/tests/test_pattern_formatter.cpp
@@ -60,12 +60,12 @@ TEST_CASE("date MM/DD/YY ", "[pattern_formatter]")
 TEST_CASE("color range test1", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("%^%v%$", spdlog::pattern_time_type::local, "\n");
-
     fmt::memory_buffer buf;
     fmt::format_to(buf, "Hello");
     fmt::memory_buffer formatted;
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, spdlog::string_view_t(buf.data(), buf.size()));
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, spdlog::string_view_t(buf.data(), buf.size()));
     formatter->format(msg, formatted);
     REQUIRE(msg.color_range_start == 0);
     REQUIRE(msg.color_range_end == 5);
@@ -76,7 +76,8 @@ TEST_CASE("color range test2", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("%^%$", spdlog::pattern_time_type::local, "\n");
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "");
     fmt::memory_buffer formatted;
     formatter->format(msg, formatted);
     REQUIRE(msg.color_range_start == 0);
@@ -88,7 +89,8 @@ TEST_CASE("color range test3", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("%^***%$");
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "ignored");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "ignored");
     fmt::memory_buffer formatted;
     formatter->format(msg, formatted);
     REQUIRE(msg.color_range_start == 0);
@@ -99,8 +101,8 @@ TEST_CASE("color range test4", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("XX%^YYY%$", spdlog::pattern_time_type::local, "\n");
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "ignored");
-
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "ignored");
     fmt::memory_buffer formatted;
     formatter->format(msg, formatted);
     REQUIRE(msg.color_range_start == 2);
@@ -112,7 +114,8 @@ TEST_CASE("color range test5", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("**%^");
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "ignored");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "ignored");
     fmt::memory_buffer formatted;
     formatter->format(msg, formatted);
     REQUIRE(msg.color_range_start == 2);
@@ -123,13 +126,26 @@ TEST_CASE("color range test6", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("**%$");
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "ignored");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "ignored");
     fmt::memory_buffer formatted;
     formatter->format(msg, formatted);
     REQUIRE(msg.color_range_start == 0);
     REQUIRE(msg.color_range_end == 2);
 }
 
+TEST_CASE("custom tag test with padding", "[pattern_formatter]")
+{
+    std::ostringstream oss;
+    auto oss_sink = std::make_shared<spdlog::sinks::ostream_sink_mt>(oss);
+    spdlog::logger oss_logger("pattern_tester", oss_sink);
+    oss_logger.set_level(spdlog::level::info);
+    oss_logger.set_formatter(std::unique_ptr<spdlog::formatter>(new spdlog::pattern_formatter("[%10q] %o %v", spdlog::pattern_time_type::local, "\n")));
+    oss_logger.set_custom_flag('q', "custom");
+    oss_logger.info("hello, world");
+    REQUIRE(oss.str() == "[    custom] %o hello, world\n");
+}
+
 //
 // Test padding
 //
@@ -200,7 +216,8 @@ TEST_CASE("clone-default-formatter", "[pattern_formatter]")
     auto formatter_1 = std::make_shared<spdlog::pattern_formatter>();
     auto formatter_2 = formatter_1->clone();
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "some message");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "some message");
 
     fmt::memory_buffer formatted_1;
     fmt::memory_buffer formatted_2;
@@ -215,7 +232,8 @@ TEST_CASE("clone-default-formatter2", "[pattern_formatter]")
     auto formatter_1 = std::make_shared<spdlog::pattern_formatter>("%+");
     auto formatter_2 = formatter_1->clone();
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "some message");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "some message");
 
     fmt::memory_buffer formatted_1;
     fmt::memory_buffer formatted_2;
@@ -230,7 +248,8 @@ TEST_CASE("clone-formatter", "[pattern_formatter]")
     auto formatter_1 = std::make_shared<spdlog::pattern_formatter>("%D %X [%] [%n] %v");
     auto formatter_2 = formatter_1->clone();
     std::string logger_name = "test";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "some message");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "some message");
 
     fmt::memory_buffer formatted_1;
     fmt::memory_buffer formatted_2;
@@ -245,7 +264,8 @@ TEST_CASE("clone-formatter-2", "[pattern_formatter]")
     auto formatter_1 = std::make_shared<spdlog::pattern_formatter>("%D %X [%] [%n] %v", pattern_time_type::utc, "xxxxxx\n");
     auto formatter_2 = formatter_1->clone();
     std::string logger_name = "test2";
-    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, "some message");
+    spdlog::log_custom_flags flags;
+    spdlog::details::log_msg msg(&logger_name, spdlog::level::info, &flags, "some message");
 
     fmt::memory_buffer formatted_1;
     fmt::memory_buffer formatted_2;