diff --git a/pkgs/mruby/.rubocop.yml b/pkgs/mruby/.rubocop.yml
index 2edecbf..47331f5 100644
--- a/pkgs/mruby/.rubocop.yml
+++ b/pkgs/mruby/.rubocop.yml
@@ -25,6 +25,10 @@ Metrics/BlockLength:
     - 'Rakefile'
     - 'test/**/*.rb'
 
+Security/YAMLLoad:
+  Exclude:
+    - 'test/**/*.rb'
+
 Style/AndOr:
   EnforcedStyle: conditionals
 
diff --git a/pkgs/mruby/mrbgem.rake b/pkgs/mruby/mrbgem.rake
index a1dd9c4..59150f6 100644
--- a/pkgs/mruby/mrbgem.rake
+++ b/pkgs/mruby/mrbgem.rake
@@ -11,7 +11,9 @@ MRuby::Gem::Specification.new 'mruby-kernaux' do |spec|
     Binding to libkernaux - auxiliary library for kernel development.
   DESCRIPTION
 
+  spec.add_test_dependency 'mruby-io'
   spec.add_test_dependency 'mruby-random'
+  spec.add_test_dependency 'mruby-yaml'
 
   spec.linker.libraries << 'kernaux'
 end
diff --git a/pkgs/mruby/mrblib/kernaux.rb b/pkgs/mruby/mrblib/kernaux.rb
index ce043f7..3b057e3 100644
--- a/pkgs/mruby/mrblib/kernaux.rb
+++ b/pkgs/mruby/mrblib/kernaux.rb
@@ -1,8 +1,32 @@
+##
+# Binding to [libkernaux](https://github.com/tailix/libkernaux) - auxiliary
+# library for kernel development.
+#
 module KernAux
   DEFAULT_ASSERT_CB = @assert_cb = lambda { |file, line, msg|
     raise AssertError, "#{file}:#{line}:#{msg}"
   }
 
+  SPRINTF1_BUFFER_SIZE = 10_000
+
+  def self.sprintf(*args)
+    args.map do |arg|
+      if arg.is_a? Array
+        sprintf1(*arg)
+      else
+        arg
+      end
+    end.join.freeze
+  end
+
+  def self.sprintf1(format, *args)
+    snprintf1(SPRINTF1_BUFFER_SIZE, format, *args).first
+  end
+
+  def self.snprintf1(_buffer_size, _format, ...)
+    ['', 0]
+  end
+
   class Error < RuntimeError; end
   class AssertError < Error; end
 end
diff --git a/pkgs/mruby/test/sprintf.rb b/pkgs/mruby/test/sprintf.rb
new file mode 100644
index 0000000..94da79b
--- /dev/null
+++ b/pkgs/mruby/test/sprintf.rb
@@ -0,0 +1,25 @@
+# TODO: implement this
+# rubocop:disable Style/BlockComments
+=begin
+assert 'KernAux.sprintf' do
+  [
+    ['',      'using regular tests'],
+    ['_orig', 'using original tests'],
+  ].each do |(suffix, description)|
+    assert description do
+      printf_yml =
+        File.expand_path("../../../../tests/printf#{suffix}.yml", __FILE__)
+
+      YAML.load(File.read(printf_yml)).each do |test|
+        expected = test['result']
+        args     = test['args']
+
+        assert "transforms #{args.inspect} to #{expected.inspect}" do
+          assert_equal expected, KernAux.sprintf(*args)
+        end
+      end
+    end
+  end
+end
+=end
+# rubocop:enable Style/BlockComments
diff --git a/pkgs/ruby/lib/kernaux.rb b/pkgs/ruby/lib/kernaux.rb
index 7a82f0c..69f64f4 100644
--- a/pkgs/ruby/lib/kernaux.rb
+++ b/pkgs/ruby/lib/kernaux.rb
@@ -65,7 +65,7 @@ module KernAux
     ##
     # Typical `printf`.
     #
-    # @param args [Array<String, Array<(String, Object)>>]
+    # @param args [Array<String, Array<(String, Object)>, Array<(String, Integer, Object)>>]
     # @return [String] formatted output
     #
     # @example
@@ -107,7 +107,7 @@ module KernAux
     # @param buffer_size [Integer] buffer size (including terminating null
     #   character)
     # @param format [String] formatting string
-    # @return [String] formatted output
+    # @return [Array<(String, Integer)>] formatted output and it's size
     #
     # @see .sprintf1 Automatic buffer size
     ##