diff --git a/Libraries/LibCore/Account.cpp b/Libraries/LibCore/Account.cpp
index a3c054557c..928c6d26a9 100644
--- a/Libraries/LibCore/Account.cpp
+++ b/Libraries/LibCore/Account.cpp
@@ -166,16 +166,16 @@ bool Account::sync()
     errno = 0;
     while ((p = getpwent())) {
         if (p->pw_uid == m_uid) {
-            new_passwd_file.appendf("%s:%s:%u:%u:%s:%s:%s\n",
-                m_username.characters(),
-                m_password_hash.characters(),
+            new_passwd_file.appendff("{}:{}:{}:{}:{}:{}:{}\n",
+                m_username,
+                m_password_hash,
                 m_uid, m_gid,
-                m_gecos.characters(),
-                m_home_directory.characters(),
-                m_shell.characters());
+                m_gecos,
+                m_home_directory,
+                m_shell);
 
         } else {
-            new_passwd_file.appendf("%s:%s:%u:%u:%s:%s:%s\n",
+            new_passwd_file.appendff("{}:{}:{}:{}:{}:{}:{}\n",
                 p->pw_name, p->pw_passwd, p->pw_uid,
                 p->pw_gid, p->pw_gecos, p->pw_dir,
                 p->pw_shell);
diff --git a/Libraries/LibCore/ArgsParser.cpp b/Libraries/LibCore/ArgsParser.cpp
index 1e168b4d16..9a66e70195 100644
--- a/Libraries/LibCore/ArgsParser.cpp
+++ b/Libraries/LibCore/ArgsParser.cpp
@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/Format.h>
 #include <AK/StringBuilder.h>
 #include <LibCore/ArgsParser.h>
 #include <getopt.h>
@@ -105,7 +106,7 @@ bool ArgsParser::parse(int argc, char** argv, bool exit_on_failure)
 
         const char* arg = found_option->requires_argument ? optarg : nullptr;
         if (!found_option->accept_value(arg)) {
-            fprintf(stderr, "\033[31mInvalid value for option \033[1m%s\033[22m, dude\033[0m\n", found_option->name_for_display().characters());
+            warnln("\033[31mInvalid value for option \033[1m{}\033[22m, dude\033[0m", found_option->name_for_display());
             print_usage_and_exit();
             return false;
         }
@@ -148,7 +149,7 @@ bool ArgsParser::parse(int argc, char** argv, bool exit_on_failure)
         for (int j = 0; j < num_values_for_arg[i]; j++) {
             const char* value = argv[optind++];
             if (!arg.accept_value(value)) {
-                fprintf(stderr, "Invalid value for argument %s\n", arg.name);
+                warnln("Invalid value for argument {}", arg.name);
                 print_usage_and_exit();
                 return false;
             }
@@ -169,67 +170,67 @@ bool ArgsParser::parse(int argc, char** argv, bool exit_on_failure)
 
 void ArgsParser::print_usage(FILE* file, const char* argv0)
 {
-    fprintf(file, "Usage:\n\t\033[1m%s\033[0m", argv0);
+    new_out(file, "Usage:\n\t\033[1m{}\033[0m", argv0);
 
     for (auto& opt : m_options) {
         if (opt.long_name && !strcmp(opt.long_name, "help"))
             continue;
         if (opt.requires_argument)
-            fprintf(file, " [%s %s]", opt.name_for_display().characters(), opt.value_name);
+            new_out(file, " [{} {}]", opt.name_for_display(), opt.value_name);
         else
-            fprintf(file, " [%s]", opt.name_for_display().characters());
+            new_out(file, " [{}]", opt.name_for_display());
     }
     for (auto& arg : m_positional_args) {
         bool required = arg.min_values > 0;
         bool repeated = arg.max_values > 1;
 
         if (required && repeated)
-            fprintf(file, " <%s...>", arg.name);
+            new_out(file, " <{}...>", arg.name);
         else if (required && !repeated)
-            fprintf(file, " <%s>", arg.name);
+            new_out(file, " <{}>", arg.name);
         else if (!required && repeated)
-            fprintf(file, " [%s...]", arg.name);
+            new_out(file, " [{}...]", arg.name);
         else if (!required && !repeated)
-            fprintf(file, " [%s]", arg.name);
+            new_out(file, " [{}]", arg.name);
     }
+    outln(file);
 
     if (!m_options.is_empty())
-        fprintf(file, "\nOptions:\n");
-
+        outln(file, "\nOptions:");
     for (auto& opt : m_options) {
         auto print_argument = [&]() {
             if (opt.value_name) {
                 if (opt.requires_argument)
-                    fprintf(file, " %s", opt.value_name);
+                    new_out(file, " {}", opt.value_name);
                 else
-                    fprintf(file, " [%s]", opt.value_name);
+                    new_out(file, " [{}]", opt.value_name);
             }
         };
-        fprintf(file, "\t");
+        new_out(file, "\t");
         if (opt.short_name) {
-            fprintf(file, "\033[1m-%c\033[0m", opt.short_name);
+            new_out(file, "\033[1m-{}\033[0m", opt.short_name);
             print_argument();
         }
         if (opt.short_name && opt.long_name)
-            fprintf(file, ", ");
+            new_out(file, ", ");
         if (opt.long_name) {
-            fprintf(file, "\033[1m--%s\033[0m", opt.long_name);
+            new_out(file, "\033[1m--{}\033[0m", opt.long_name);
             print_argument();
         }
 
         if (opt.help_string)
-            fprintf(file, "\t%s", opt.help_string);
-        fprintf(file, "\n");
+            new_out(file, "\t{}", opt.help_string);
+        outln(file);
     }
 
     if (!m_positional_args.is_empty())
-        fprintf(file, "\nArguments:\n");
+        outln(file, "\nArguments:");
 
     for (auto& arg : m_positional_args) {
-        fprintf(file, "\t\033[1m%s\033[0m", arg.name);
+        new_out(file, "\t\033[1m{}\033[0m", arg.name);
         if (arg.help_string)
-            fprintf(file, "\t%s", arg.help_string);
-        fprintf(file, "\n");
+            new_out(file, "\t{}", arg.help_string);
+        outln(file);
     }
 }
 
diff --git a/Libraries/LibCore/Command.cpp b/Libraries/LibCore/Command.cpp
index 019f6c0e98..5ecc5d940d 100644
--- a/Libraries/LibCore/Command.cpp
+++ b/Libraries/LibCore/Command.cpp
@@ -110,7 +110,7 @@ String command(const String& program, const Vector<String>& arguments, Optional<
 
     if (WEXITSTATUS(wstatus) != 0) {
 #    ifdef DBG_FAILED_COMMANDS
-        dbg() << "command failed. stderr: " << read_all_from_pipe(stderr_pipe);
+        dbgln("command failed. stderr: {}", read_all_from_pipe(stderr_pipe));
 #    endif
         return {};
     }
diff --git a/Libraries/LibCore/ConfigFile.cpp b/Libraries/LibCore/ConfigFile.cpp
index 267513e9da..c004a38dcb 100644
--- a/Libraries/LibCore/ConfigFile.cpp
+++ b/Libraries/LibCore/ConfigFile.cpp
@@ -37,7 +37,7 @@ namespace Core {
 NonnullRefPtr<ConfigFile> ConfigFile::get_for_lib(const String& lib_name)
 {
     String directory = StandardPaths::config_directory();
-    auto path = String::format("%s/lib/%s.ini", directory.characters(), lib_name.characters());
+    auto path = String::formatted("{}/lib/{}.ini", directory, lib_name);
 
     return adopt(*new ConfigFile(path));
 }
@@ -45,13 +45,13 @@ NonnullRefPtr<ConfigFile> ConfigFile::get_for_lib(const String& lib_name)
 NonnullRefPtr<ConfigFile> ConfigFile::get_for_app(const String& app_name)
 {
     String directory = StandardPaths::config_directory();
-    auto path = String::format("%s/%s.ini", directory.characters(), app_name.characters());
+    auto path = String::formatted("{}/{}.ini", directory, app_name);
     return adopt(*new ConfigFile(path));
 }
 
 NonnullRefPtr<ConfigFile> ConfigFile::get_for_system(const String& app_name)
 {
-    auto path = String::format("/etc/%s.ini", app_name.characters());
+    auto path = String::formatted("/etc/{}.ini", app_name);
     return adopt(*new ConfigFile(path));
 }
 
@@ -162,7 +162,7 @@ void ConfigFile::write_bool_entry(const String& group, const String& key, bool v
 }
 void ConfigFile::write_color_entry(const String& group, const String& key, Color value)
 {
-    write_entry(group, key, String::format("%d,%d,%d,%d", value.red(), value.green(), value.blue(), value.alpha()));
+    write_entry(group, key, String::formatted("{},{},{},{}", value.red(), value.green(), value.blue(), value.alpha()));
 }
 
 bool ConfigFile::sync()
@@ -175,10 +175,10 @@ bool ConfigFile::sync()
         return false;
 
     for (auto& it : m_groups) {
-        fprintf(fp, "[%s]\n", it.key.characters());
+        outln(fp, "[{}]", it.key);
         for (auto& jt : it.value)
-            fprintf(fp, "%s=%s\n", jt.key.characters(), jt.value.characters());
-        fprintf(fp, "\n");
+            outln(fp, "{}={}", jt.key, jt.value);
+        outln(fp);
     }
 
     fclose(fp);
@@ -190,10 +190,10 @@ bool ConfigFile::sync()
 void ConfigFile::dump() const
 {
     for (auto& it : m_groups) {
-        printf("[%s]\n", it.key.characters());
+        outln("[{}]", it.key);
         for (auto& jt : it.value)
-            printf("%s=%s\n", jt.key.characters(), jt.value.characters());
-        printf("\n");
+            outln("{}={}", jt.key, jt.value);
+        outln();
     }
 }
 
diff --git a/Libraries/LibCore/DateTime.cpp b/Libraries/LibCore/DateTime.cpp
index 58f914a629..804abac3de 100644
--- a/Libraries/LibCore/DateTime.cpp
+++ b/Libraries/LibCore/DateTime.cpp
@@ -251,7 +251,7 @@ String DateTime::to_string(const String& format) const
 
 bool DateTime::is_before(const String& other) const
 {
-    auto now_string = String::format("%04d%02d%02d%02d%02d%02dZ", year(), month(), weekday(), hour(), minute(), second());
+    auto now_string = String::formatted("{:04}{:02}{:02}{:02}{:02}{:02}Z", year(), month(), weekday(), hour(), minute(), second());
     return __builtin_strcasecmp(now_string.characters(), other.characters()) < 0;
 }
 
@@ -259,4 +259,5 @@ const LogStream& operator<<(const LogStream& stream, const DateTime& value)
 {
     return stream << value.to_string();
 }
+
 }
diff --git a/Libraries/LibCore/DirIterator.cpp b/Libraries/LibCore/DirIterator.cpp
index 73f7426976..3dbeecf24f 100644
--- a/Libraries/LibCore/DirIterator.cpp
+++ b/Libraries/LibCore/DirIterator.cpp
@@ -96,7 +96,7 @@ String DirIterator::next_path()
 
 String DirIterator::next_full_path()
 {
-    return String::format("%s/%s", m_path.characters(), next_path().characters());
+    return String::formatted("{}/{}", m_path, next_path());
 }
 
 String find_executable_in_path(String filename)
@@ -109,7 +109,7 @@ String find_executable_in_path(String filename)
     }
 
     for (auto directory : String { getenv("PATH") }.split(':')) {
-        auto fullpath = String::format("%s/%s", directory.characters(), filename.characters());
+        auto fullpath = String::formatted("{}/{}", directory, filename);
 
         if (access(fullpath.characters(), X_OK) == 0)
             return fullpath;
diff --git a/Libraries/LibCore/EventLoop.cpp b/Libraries/LibCore/EventLoop.cpp
index 28b1f553da..97a9ce26bc 100644
--- a/Libraries/LibCore/EventLoop.cpp
+++ b/Libraries/LibCore/EventLoop.cpp
@@ -102,7 +102,7 @@ public:
             int nread = m_socket->read((u8*)&length, sizeof(length));
             if (nread == 0) {
 #ifdef EVENTLOOP_DEBUG
-                dbg() << "RPC client disconnected";
+                dbgln("RPC client disconnected");
 #endif
                 shutdown();
                 return;
@@ -112,7 +112,7 @@ public:
 
             auto request_json = JsonValue::from_string(request);
             if (!request_json.has_value() || !request_json.value().is_object()) {
-                dbg() << "RPC client sent invalid request";
+                dbgln("RPC client sent invalid request");
                 shutdown();
                 return;
             }
@@ -139,7 +139,7 @@ public:
         auto type = request.get("type").as_string_or({});
 
         if (type.is_null()) {
-            dbg() << "RPC client sent request without type field";
+            dbgln("RPC client sent request without type field");
             return;
         }
 
@@ -245,12 +245,12 @@ EventLoop::EventLoop()
 
         if (!s_rpc_server) {
             if (!start_rpc_server())
-                dbg() << "Core::EventLoop: Failed to start an RPC server";
+                dbgln("Core::EventLoop: Failed to start an RPC server");
         }
     }
 
 #ifdef EVENTLOOP_DEBUG
-    dbg() << getpid() << " Core::EventLoop constructed :)";
+    dbgln("{} Core::EventLoop constructed :)", getpid());
 #endif
 }
 
@@ -304,7 +304,7 @@ EventLoop& EventLoop::current()
 void EventLoop::quit(int code)
 {
 #ifdef EVENTLOOP_DEBUG
-    dbg() << "Core::EventLoop::quit(" << code << ")";
+    dbgln("Core::EventLoop::quit({})", code);
 #endif
     m_exit_requested = true;
     m_exit_code = code;
@@ -313,7 +313,7 @@ void EventLoop::quit(int code)
 void EventLoop::unquit()
 {
 #ifdef EVENTLOOP_DEBUG
-    dbg() << "Core::EventLoop::unquit()";
+    dbgln("Core::EventLoop::unquit()");
 #endif
     m_exit_requested = false;
     m_exit_code = 0;
@@ -368,7 +368,7 @@ void EventLoop::pump(WaitMode mode)
         auto& event = *queued_event.event;
 #ifdef EVENTLOOP_DEBUG
         if (receiver)
-            dbg() << "Core::EventLoop: " << *receiver << " event " << (int)event.type();
+            dbgln("Core::EventLoop: {} event {}", *receiver, event.type());
 #endif
         if (!receiver) {
             switch (event.type()) {
@@ -377,13 +377,13 @@ void EventLoop::pump(WaitMode mode)
                 return;
             default:
 #ifdef EVENTLOOP_DEBUG
-                dbg() << "Event type " << event.type() << " with no receiver :(";
+                dbgln("Event type {} with no receiver :(", event.type());
 #endif
                 break;
             }
         } else if (event.type() == Event::Type::DeferredInvoke) {
 #ifdef DEFERRED_INVOKE_DEBUG
-            dbg() << "DeferredInvoke: receiver = " << receiver->class_name() << "{" << receiver << "}";
+            dbgln("DeferredInvoke: receiver = {}", *receiver);
 #endif
             static_cast<DeferredInvocationEvent&>(event).m_invokee(*receiver);
         } else {
@@ -394,7 +394,7 @@ void EventLoop::pump(WaitMode mode)
         if (m_exit_requested) {
             LOCKER(m_private->lock);
 #ifdef EVENTLOOP_DEBUG
-            dbg() << "Core::EventLoop: Exit requested. Rejigging " << (events.size() - i) << " events.";
+            dbgln("Core::EventLoop: Exit requested. Rejigging {} events.", events.size() - i);
 #endif
             decltype(m_queued_events) new_event_queue;
             new_event_queue.ensure_capacity(m_queued_events.size() + events.size());
@@ -411,7 +411,7 @@ void EventLoop::post_event(Object& receiver, NonnullOwnPtr<Event>&& event)
 {
     LOCKER(m_private->lock);
 #ifdef EVENTLOOP_DEBUG
-    dbg() << "Core::EventLoop::post_event: {" << m_queued_events.size() << "} << receiver=" << receiver << ", event=" << event;
+    dbgln("Core::EventLoop::post_event: ({}) << receivier={}, event={}", m_queued_events.size(), receiver, event);
 #endif
     m_queued_events.empend(receiver, move(event));
 }
@@ -421,7 +421,7 @@ EventLoop::SignalHandlers::SignalHandlers(int signo)
     , m_original_handler(signal(signo, EventLoop::handle_signal))
 {
 #ifdef EVENTLOOP_DEBUG
-    dbg() << "Core::EventLoop: Registered handler for signal " << m_signo;
+    dbgln("Core::EventLoop: Registered handler for signal {}", m_signo);
 #endif
 }
 
@@ -429,7 +429,7 @@ EventLoop::SignalHandlers::~SignalHandlers()
 {
     if (m_valid) {
 #ifdef EVENTLOOP_DEBUG
-        dbg() << "Core::EventLoop: Unregistering handler for signal " << m_signo;
+        dbgln("Core::EventLoop: Unregistering handler for signal {}", m_signo);
 #endif
         signal(m_signo, m_original_handler);
     }
@@ -461,7 +461,7 @@ void EventLoop::dispatch_signal(int signo)
     auto handlers = s_signal_handlers.find(signo);
     if (handlers != s_signal_handlers.end()) {
 #ifdef EVENTLOOP_DEBUG
-        dbg() << "Core::EventLoop: dispatching signal " << signo;
+        dbgln("Core::EventLoop: dispatching signal {}", signo);
 #endif
         handlers->value.dispatch();
     }
@@ -602,7 +602,7 @@ try_select_again:
             goto try_select_again;
         }
 #ifdef EVENTLOOP_DEBUG
-        dbg() << "Core::EventLoop::wait_for_event: " << marked_fd_count << " (" << saved_errno << ": " << strerror(saved_errno) << ")";
+        dbgln("Core::EventLoop::wait_for_event: {} ({}: {})", marked_fd_count, saved_errno, strerror(saved_errno));
 #endif
         // Blow up, similar to Core::safe_syscall.
         ASSERT_NOT_REACHED();
@@ -645,7 +645,7 @@ try_select_again:
             continue;
         }
 #ifdef EVENTLOOP_DEBUG
-        dbg() << "Core::EventLoop: Timer " << timer.timer_id << " has expired, sending Core::TimerEvent to " << timer.owner;
+        dbgln("Core::EventLoop: Timer {} has expired, sending Core::TimerEvent to {}", timer.timer_id, timer.owner);
 #endif
         post_event(*timer.owner, make<TimerEvent>(timer.timer_id));
         if (timer.should_reload) {