diff --git a/lib/bmg/writer.rb b/lib/bmg/writer.rb
index 02446cf..8fd229c 100644
--- a/lib/bmg/writer.rb
+++ b/lib/bmg/writer.rb
@@ -12,6 +12,23 @@ def infer_headers(from)
       attrlist ? output_preferences.order_attrlist(attrlist) : nil
     end
 
+    def infer_formats(relation, headers)
+      relation
+        .page([], 1, page_size: 100)
+        .summarize([], headers.each_with_object({}){|h,memo|
+          memo[h] = Summarizer.multiple({
+            :count => Summarizer.count,
+            :min => Summarizer.min(h.to_sym),
+            :max => Summarizer.max(h.to_sym),
+            :distinct => Summarizer.distinct(h.to_sym),
+            :types => Summarizer.by_proc{|t,memo| ((memo || []) << t[h.to_sym].class).uniq },
+            :length_80 => Summarizer.percentile(80){|t| t[h.to_sym].to_s.size }
+          })
+          memo
+        })
+        .tap{|r| puts JSON.pretty_generate(r.one) }
+    end
+
   end # module Writer
 end # module Bmg
 require_relative 'writer/csv'
diff --git a/lib/bmg/writer/xlsx.rb b/lib/bmg/writer/xlsx.rb
index 0789b03..626ddc3 100644
--- a/lib/bmg/writer/xlsx.rb
+++ b/lib/bmg/writer/xlsx.rb
@@ -24,9 +24,10 @@ def _call(relation, path)
         @workbook = WriteXLSX.new(path)
         @worksheet = workbook.add_worksheet
 
-        headers = infer_headers(relation.type)
+        headers, formats = infer_headers(relation.type), nil
         relation.each_with_index do |tuple,i|
           headers = infer_headers(tuple) if headers.nil?
+          formats = infer_formats(relation, headers) if formats.nil?
           headers.each_with_index do |h,i|
             worksheet.write_string(0, i, h)
           end if i == 0
diff --git a/spec/unit/writer/test_xlsx.rb b/spec/unit/writer/test_xlsx.rb
index 7096217..2cf6dbc 100644
--- a/spec/unit/writer/test_xlsx.rb
+++ b/spec/unit/writer/test_xlsx.rb
@@ -14,7 +14,8 @@ module Writer
       let(:relation) {
         Relation.new [
           { id: 1, name: "Bernard", nonnum: "1", when: date },
-          { id: 2, name: "Yoann",   nonnum: "2", when: date }
+          { id: 2, name: "Yoann",   nonnum: "2", when: date },
+          { id: 3, name: "Louis",   nonnum: "1", when: date+10 }
         ]
       }