diff --git a/lib/roast/cogs/agent/providers/claude/tool_use.rb b/lib/roast/cogs/agent/providers/claude/tool_use.rb
index 0d6404a5..f6354f2d 100644
--- a/lib/roast/cogs/agent/providers/claude/tool_use.rb
+++ b/lib/roast/cogs/agent/providers/claude/tool_use.rb
@@ -166,6 +166,33 @@ def format_write
               "WRITE #{file_path} \"#{preview}\" (+#{count} #{line_label})"
             end
 
+            # Formats an Edit tool-use line.
+            #
+            # Input fields:
+            #   :file_path   (String) – absolute path to edit    [required]
+            #   :old_string  (String) – text being replaced      [required]
+            #   :new_string  (String) – replacement text         [required]
+            #   :replace_all (bool)   – replace every occurrence [optional]
+            #
+            # Output: "EDIT <file_path> (-<old> +<new> lines)", where <old> and
+            # <new> are the line counts of :old_string and :new_string. The
+            # count is always labeled " lines"; " · replace all" is appended
+            # when :replace_all is set.
+            #
+            # Examples:
+            #   EDIT /app/models/user.rb (-6 +6 lines)
+            #   EDIT /config/routes.rb (-1 +2 lines · replace all)
+            #
+            #: () -> String
+            def format_edit
+              file_path, old_string, new_string = input.values_at(:file_path, :old_string, :new_string)
+              old_count = old_string.to_s.lines.length
+              new_count = new_string.to_s.lines.length
+              details = "-#{old_count} +#{new_count} lines"
+              details = "#{details} · replace all" if input[:replace_all]
+              "EDIT #{file_path} (#{details})"
+            end
+
             #: () -> String
             def format_unknown
               "UNKNOWN [#{name}] #{input.inspect}"
diff --git a/test/roast/cogs/agent/providers/claude/tool_use_test.rb b/test/roast/cogs/agent/providers/claude/tool_use_test.rb
index 905ac5a6..1af18b43 100644
--- a/test/roast/cogs/agent/providers/claude/tool_use_test.rb
+++ b/test/roast/cogs/agent/providers/claude/tool_use_test.rb
@@ -193,6 +193,41 @@ class ToolUseTest < ActiveSupport::TestCase
               assert_equal "WRITE /a.rb \"#{truncated}\" (+1 line)", output
             end
 
+            # format_edit
+
+            test "format_edit shows the line counts of a single-line replacement" do
+              tool_use = ToolUse.new(name: :edit, input: { file_path: "/a.rb", old_string: "foo", new_string: "bar" })
+
+              output = tool_use.format
+
+              assert_equal "EDIT /a.rb (-1 +1 lines)", output
+            end
+
+            test "format_edit counts the lines spanned by each string" do
+              tool_use = ToolUse.new(name: :edit, input: { file_path: "/a.rb", old_string: "a\nb", new_string: "x" })
+
+              output = tool_use.format
+
+              assert_equal "EDIT /a.rb (-2 +1 lines)", output
+            end
+
+            test "format_edit appends replace all when the flag is set" do
+              input = { file_path: "/a.rb", old_string: "foo", new_string: "bar", replace_all: true }
+              tool_use = ToolUse.new(name: :edit, input: input)
+
+              output = tool_use.format
+
+              assert_equal "EDIT /a.rb (-1 +1 lines · replace all)", output
+            end
+
+            test "format_edit shows zero counts when the strings are absent" do
+              tool_use = ToolUse.new(name: :edit, input: { file_path: "/a.rb" })
+
+              output = tool_use.format
+
+              assert_equal "EDIT /a.rb (-0 +0 lines)", output
+            end
+
             test "format calls format_unknown for unknown tool" do
               tool_use = ToolUse.new(name: :unknown_tool, input: { arg: "value" })