diff --git a/lib/prism/helpers/output_safety.rb b/lib/prism/helpers/output_safety.rb
new file mode 100644
index 0000000..6e739c5
--- /dev/null
+++ b/lib/prism/helpers/output_safety.rb
@@ -0,0 +1,100 @@
+require 'cgi'
+
+module Prism
+  module Helpers
+    class SafeString < String
+      def html_safe?
+        true
+      end
+
+      def html_safe
+        self
+      end
+
+      def to_s
+        self
+      end
+
+      def to_str
+        String.new(self)
+      end
+
+      def <<(other)
+        super(coerce(other))
+      end
+      alias_method :concat, :<<
+
+      def +(other)
+        dup.concat(other)
+      end
+
+      def *(times)
+        self.class.new(String.instance_method(:*).bind_call(self, times))
+      end
+
+      private
+
+      def coerce(other)
+        other.is_a?(SafeString) ? other.to_str : CGI.escapeHTML(other.to_s)
+      end
+    end
+
+    class SafeBuffer < SafeString
+      def append(other)
+        self << other
+        self
+      end
+    end
+
+    module OutputSafety
+      ENCODING_MAP = {
+        '&' => '&amp;',
+        '>' => '&gt;',
+        '<' => '&lt;',
+        '"' => '&quot;',
+        "'" => '&#39;'
+      }.freeze
+
+      module_function
+
+      def html_safe(value)
+        value.is_a?(SafeString) ? value : SafeString.new(value.to_s)
+      end
+
+      def html_escape(value)
+        return value if value.is_a?(SafeString)
+        SafeString.new(CGI.escapeHTML(value.to_s))
+      end
+
+      def escape_once(value)
+        return value if value.is_a?(SafeString)
+        escaped = value.to_s.gsub(/["><']|&(?!([a-zA-Z]+|(#\d+)|(#x[0-9a-fA-F]+));)/, ENCODING_MAP)
+        SafeString.new(escaped)
+      end
+
+      def safe?(value)
+        value.is_a?(SafeString)
+      end
+
+      def safe_join(parts, separator = '')
+        safe_separator = html_escape(separator).to_str
+        joined = Array(parts).flatten.map { |part| html_escape(part).to_str }.join(safe_separator)
+        SafeString.new(joined)
+      end
+    end
+  end
+end
+
+class String
+  unless method_defined?(:html_safe?)
+    def html_safe?
+      false
+    end
+  end
+
+  unless method_defined?(:html_safe)
+    def html_safe
+      Prism::Helpers::SafeString.new(self)
+    end
+  end
+end