diff --git a/doc/maintainers.rdoc b/doc/maintainers.rdoc
index b453a924e0..6f69ffce77 100644
--- a/doc/maintainers.rdoc
+++ b/doc/maintainers.rdoc
@@ -277,10 +277,6 @@ Yukihiro Matsumoto (matz)
   _unmaintained_
   https://github.com/ruby/tmpdir
   https://rubygems.org/gems/tmpdir
-[lib/tracer.rb]
-  Keiju ISHITSUKA (keiju)
-  https://github.com/ruby/tracer
-  https://rubygems.org/gems/tracer
 [lib/tsort.rb]
   Tanaka Akira (akr)
   https://github.com/ruby/tsort
diff --git a/doc/standard_library.rdoc b/doc/standard_library.rdoc
index e4418aea81..7300b723e2 100644
--- a/doc/standard_library.rdoc
+++ b/doc/standard_library.rdoc
@@ -72,7 +72,6 @@ Tempfile:: A utility class for managing temporary files
 Time:: Extends the Time class with methods for parsing and conversion
 Timeout:: Auto-terminate potentially long-running operations in Ruby
 tmpdir.rb:: Extends the Dir class to manage the OS temporary file path
-Tracer:: Outputs a source level execution trace of a Ruby program
 TSort:: Topological sorting using Tarjan's algorithm
 un.rb:: Utilities to replace common UNIX commands
 URI:: A Ruby module providing support for Uniform Resource Identifiers
diff --git a/lib/tracer.rb b/lib/tracer.rb
deleted file mode 100644
index 9014d80da5..0000000000
--- a/lib/tracer.rb
+++ /dev/null
@@ -1,292 +0,0 @@
-# frozen_string_literal: false
-#--
-# $Release Version: 0.3$
-# $Revision: 1.12 $
-
-##
-# Outputs a source level execution trace of a Ruby program.
-#
-# It does this by registering an event handler with Kernel#set_trace_func for
-# processing incoming events.  It also provides methods for filtering unwanted
-# trace output (see Tracer.add_filter, Tracer.on, and Tracer.off).
-#
-# == Example
-#
-# Consider the following Ruby script
-#
-#   class A
-#     def square(a)
-#       return a*a
-#     end
-#   end
-#
-#   a = A.new
-#   a.square(5)
-#
-# Running the above script using <code>ruby -r tracer example.rb</code> will
-# output the following trace to STDOUT (Note you can also explicitly
-# <code>require 'tracer'</code>)
-#
-#   #0:<internal:lib/rubygems/custom_require>:38:Kernel:<: -
-#   #0:example.rb:3::-: class A
-#   #0:example.rb:3::C: class A
-#   #0:example.rb:4::-:   def square(a)
-#   #0:example.rb:7::E: end
-#   #0:example.rb:9::-: a = A.new
-#   #0:example.rb:10::-: a.square(5)
-#   #0:example.rb:4:A:>:   def square(a)
-#   #0:example.rb:5:A:-:     return a*a
-#   #0:example.rb:6:A:<:   end
-#    |  |         | |  |
-#    |  |         | |   ---------------------+ event
-#    |  |         |  ------------------------+ class
-#    |  |          --------------------------+ line
-#    |   ------------------------------------+ filename
-#     ---------------------------------------+ thread
-#
-# Symbol table used for displaying incoming events:
-#
-# +}+:: call a C-language routine
-# +{+:: return from a C-language routine
-# +>+:: call a Ruby method
-# +C+:: start a class or module definition
-# +E+:: finish a class or module definition
-# +-+:: execute code on a new line
-# +^+:: raise an exception
-# +<+:: return from a Ruby method
-#
-# == Copyright
-#
-# by Keiju ISHITSUKA(keiju@ishitsuka.com)
-#
-class Tracer
-  VERSION = "0.1.1"
-
-  class << self
-    # display additional debug information (defaults to false)
-    attr_accessor :verbose
-    alias verbose? verbose
-
-    # output stream used to output trace (defaults to STDOUT)
-    attr_accessor :stdout
-
-    # mutex lock used by tracer for displaying trace output
-    attr_reader :stdout_mutex
-
-    # display process id in trace output (defaults to false)
-    attr_accessor :display_process_id
-    alias display_process_id? display_process_id
-
-    # display thread id in trace output (defaults to true)
-    attr_accessor :display_thread_id
-    alias display_thread_id? display_thread_id
-
-    # display C-routine calls in trace output (defaults to false)
-    attr_accessor :display_c_call
-    alias display_c_call? display_c_call
-  end
-
-  Tracer::stdout = STDOUT
-  Tracer::verbose = false
-  Tracer::display_process_id = false
-  Tracer::display_thread_id = true
-  Tracer::display_c_call = false
-
-  @stdout_mutex = Thread::Mutex.new
-
-  # Symbol table used for displaying trace information
-  EVENT_SYMBOL = {
-    "line" => "-",
-    "call" => ">",
-    "return" => "<",
-    "class" => "C",
-    "end" => "E",
-    "raise" => "^",
-    "c-call" => "}",
-    "c-return" => "{",
-    "unknown" => "?"
-  }
-
-  def initialize # :nodoc:
-    @threads = Hash.new
-    if defined? Thread.main
-      @threads[Thread.main.object_id] = 0
-    else
-      @threads[Thread.current.object_id] = 0
-    end
-
-    @get_line_procs = {}
-
-    @filters = []
-  end
-
-  def stdout # :nodoc:
-    Tracer.stdout
-  end
-
-  def on # :nodoc:
-    if block_given?
-      on
-      begin
-        yield
-      ensure
-        off
-      end
-    else
-      set_trace_func method(:trace_func).to_proc
-      stdout.print "Trace on\n" if Tracer.verbose?
-    end
-  end
-
-  def off # :nodoc:
-    set_trace_func nil
-    stdout.print "Trace off\n" if Tracer.verbose?
-  end
-
-  def add_filter(p = nil, &b) # :nodoc:
-    p ||= b
-    @filters.push p
-  end
-
-  def set_get_line_procs(file, p = nil, &b) # :nodoc:
-    p ||= b
-    @get_line_procs[file] = p
-  end
-
-  def get_line(file, line) # :nodoc:
-    if p = @get_line_procs[file]
-      return p.call(line)
-    end
-
-    unless list = SCRIPT_LINES__[file]
-      list = File.readlines(file) rescue []
-      SCRIPT_LINES__[file] = list
-    end
-
-    if l = list[line - 1]
-      l
-    else
-      "-\n"
-    end
-  end
-
-  def get_thread_no # :nodoc:
-    if no = @threads[Thread.current.object_id]
-      no
-    else
-      @threads[Thread.current.object_id] = @threads.size
-    end
-  end
-
-  def trace_func(event, file, line, id, binding, klass, *) # :nodoc:
-    return if file == __FILE__
-
-    for p in @filters
-      return unless p.call event, file, line, id, binding, klass
-    end
-
-    return unless Tracer::display_c_call? or
-      event != "c-call" && event != "c-return"
-
-    Tracer::stdout_mutex.synchronize do
-      if EVENT_SYMBOL[event]
-        stdout.printf("<%d>", $$) if Tracer::display_process_id?
-        stdout.printf("#%d:", get_thread_no) if Tracer::display_thread_id?
-        if line == 0
-          source = "?\n"
-        else
-          source = get_line(file, line)
-        end
-        stdout.printf("%s:%d:%s:%s: %s",
-               file,
-               line,
-               klass || '',
-               EVENT_SYMBOL[event],
-               source)
-      end
-    end
-
-  end
-
-  # Reference to singleton instance of Tracer
-  Single = new
-
-  ##
-  # Start tracing
-  #
-  # === Example
-  #
-  #   Tracer.on
-  #   # code to trace here
-  #   Tracer.off
-  #
-  # You can also pass a block:
-  #
-  #   Tracer.on {
-  #     # trace everything in this block
-  #   }
-
-  def Tracer.on
-    if block_given?
-      Single.on{yield}
-    else
-      Single.on
-    end
-  end
-
-  ##
-  # Disable tracing
-
-  def Tracer.off
-    Single.off
-  end
-
-  ##
-  # Register an event handler <code>p</code> which is called every time a line
-  # in +file_name+ is executed.
-  #
-  # Example:
-  #
-  #   Tracer.set_get_line_procs("example.rb", lambda { |line|
-  #     puts "line number executed is #{line}"
-  #   })
-
-  def Tracer.set_get_line_procs(file_name, p = nil, &b)
-    p ||= b
-    Single.set_get_line_procs(file_name, p)
-  end
-
-  ##
-  # Used to filter unwanted trace output
-  #
-  # Example which only outputs lines of code executed within the Kernel class:
-  #
-  #   Tracer.add_filter do |event, file, line, id, binding, klass, *rest|
-  #     "Kernel" == klass.to_s
-  #   end
-
-  def Tracer.add_filter(p = nil, &b)
-    p ||= b
-    Single.add_filter(p)
-  end
-end
-
-# :stopdoc:
-SCRIPT_LINES__ = {} unless defined? SCRIPT_LINES__
-
-if $0 == __FILE__
-  # direct call
-
-  $0 = ARGV[0]
-  ARGV.shift
-  Tracer.on
-  require $0
-else
-  # call Tracer.on only if required by -r command-line option
-  count = caller.count {|bt| %r%/rubygems/core_ext/kernel_require\.rb:% !~ bt}
-  if (defined?(Gem) and count == 0) or
-     (!defined?(Gem) and count <= 1)
-    Tracer.on
-  end
-end
-# :startdoc:
diff --git a/lib/tracer/tracer.gemspec b/lib/tracer/tracer.gemspec
deleted file mode 100644
index de9401da2c..0000000000
--- a/lib/tracer/tracer.gemspec
+++ /dev/null
@@ -1,25 +0,0 @@
-# frozen_string_literal: true
-
-name = File.basename(__FILE__, ".gemspec")
-version = ["lib", Array.new(name.count("-")+1, "..").join("/")].find do |dir|
-  break File.foreach(File.join(__dir__, dir, "#{name.tr('-', '/')}.rb")) do |line|
-    /^\s*VERSION\s*=\s*"(.*)"/ =~ line and break $1
-  end rescue nil
-end
-
-Gem::Specification.new do |spec|
-  spec.name          = name
-  spec.version       = version
-  spec.authors       = ["Keiju ISHITSUKA"]
-  spec.email         = ["keiju@ruby-lang.org"]
-
-  spec.summary       = %q{Outputs a source level execution trace of a Ruby program.}
-  spec.description   = %q{Outputs a source level execution trace of a Ruby program.}
-  spec.homepage      = "https://github.com/ruby/tracer"
-  spec.licenses      = ["Ruby", "BSD-2-Clause"]
-
-  spec.files         = ["Gemfile", "LICENSE.txt", "README.md", "Rakefile", "lib/tracer.rb", "tracer.gemspec"]
-  spec.bindir        = "exe"
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
-  spec.require_paths = ["lib"]
-end
diff --git a/test/test_tracer.rb b/test/test_tracer.rb
deleted file mode 100644
index 0a098332ea..0000000000
--- a/test/test_tracer.rb
+++ /dev/null
@@ -1,234 +0,0 @@
-# frozen_string_literal: false
-require 'test/unit'
-require 'tmpdir'
-
-class TestTracer < Test::Unit::TestCase
-  include EnvUtil
-
-  def test_tracer_with_option_r
-    assert_in_out_err(%w[-rtracer -e 1]) do |(*lines),|
-      case lines.size
-      when 1
-        # do nothing
-      else
-        assert_match(%r{rubygems/core_ext/kernel_require\.rb:\d+:Kernel:<:}, lines[0])
-      end
-      assert_equal "#0:-e:1::-: 1", lines.last
-    end
-  end
-
-  def test_tracer_with_option_r_without_gems
-    assert_in_out_err(%w[--disable-gems -rtracer -e 1]) do |(*lines),|
-      assert_equal 1, lines.size, "unexpected output from `ruby --disable-gems -rtracer -e 1`"
-      assert_equal "#0:-e:1::-: 1", lines.last
-    end
-  end
-
-  def test_tracer_with_require
-    Dir.mktmpdir("test_ruby_tracer") do |dir|
-      script = File.join(dir, "require_tracer.rb")
-      open(script, "w") do |f|
-        f.print <<-EOF
-require 'tracer'
-1
-        EOF
-      end
-      assert_in_out_err([script]) do |(*lines),|
-        assert_empty(lines)
-      end
-    end
-  end
-
-  def test_tracer_with_require_without_gems
-    Dir.mktmpdir("test_ruby_tracer") do |dir|
-      script = File.join(dir, "require_tracer.rb")
-      open(script, "w") do |f|
-        f.print <<-EOF
-require 'tracer'
-1
-        EOF
-      end
-      assert_in_out_err(["--disable-gems", script]) do |(*lines),|
-        assert_empty(lines)
-      end
-    end
-  end
-
-  def test_tracer_by_add_filter_with_block
-    Dir.mktmpdir("test_ruby_tracer") do |dir|
-      script = File.join(dir, "require_tracer.rb")
-      open(script, "w") do |f|
-        f.print <<-'EOF'
-require 'tracer'
-
-class Hoge
-  def Hoge.fuga(i)
-    "fuga #{i}"
-  end
-end
-
-Tracer.add_filter {|event, file, line, id, binding, klass|
-  event =~ /line/ and klass.to_s =~ /hoge/i
-}
-Tracer.on
-for i in 0..3
-  puts Hoge.fuga(i) if i % 3 == 0
-end
-Tracer.off
-        EOF
-      end
-      assert_in_out_err([script]) do |(*lines), err|
-        expected = [
-          "#0:#{script}:5:Hoge:-:     \"fuga \#{i}\"",
-          "fuga 0",
-          "#0:#{script}:5:Hoge:-:     \"fuga \#{i}\"",
-          "fuga 3"
-        ]
-        assert_equal(expected, lines)
-        assert_empty(err)
-      end
-    end
-  end
-
-  def test_tracer_by_add_filter_with_proc
-    Dir.mktmpdir("test_ruby_tracer") do |dir|
-      script = File.join(dir, "require_tracer.rb")
-      open(script, "w") do |f|
-        f.print <<-'EOF'
-require 'tracer'
-
-class Hoge
-  def Hoge.fuga(i)
-    "fuga #{i}"
-  end
-end
-
-a_proc_to_add_filter = proc {|event, file, line, id, binding, klass|
-  event =~ /line/ and klass.to_s =~ /hoge/i
-}
-Tracer.add_filter(a_proc_to_add_filter)
-Tracer.on
-for i in 0..3
-  puts Hoge.fuga(i) if i % 3 == 0
-end
-Tracer.off
-        EOF
-      end
-      assert_in_out_err([script]) do |(*lines), err|
-        expected = [
-          "#0:#{script}:5:Hoge:-:     \"fuga \#{i}\"",
-          "fuga 0",
-          "#0:#{script}:5:Hoge:-:     \"fuga \#{i}\"",
-          "fuga 3"
-        ]
-        assert_equal(expected, lines)
-        assert_empty(err)
-      end
-    end
-  end
-
-  def test_tracer_by_set_get_line_procs_with_block
-    Dir.mktmpdir("test_ruby_tracer") do |dir|
-      dummy_script = File.join(dir, "dummy.rb")
-      open(dummy_script, "w") do |f|
-        f.print <<-'EOF'
-class Dummy
-  def initialize
-    @number = 135
-  end
-  attr :number
-end
-        EOF
-      end
-      dummy_script = File.realpath dummy_script
-      script = File.join(dir, "require_tracer.rb")
-      open(script, "w") do |f|
-        f.print <<-EOF
-require 'tracer'
-
-Tracer.set_get_line_procs('#{dummy_script}') { |line|
-  str = %{\\n}
-  str = %{!!\\n} if line >= 3 and line <= 6
-  str
-}
-Tracer.on
-require_relative 'dummy'
-
-dm = Dummy.new
-puts dm.number
-        EOF
-      end
-      assert_in_out_err([script]) do |(*lines), err|
-        expected = [
-          "#0:#{script}:9::-: require_relative 'dummy'",
-          "#0:#{dummy_script}:1::-: ",
-          "#0:#{dummy_script}:1::C: ",
-          "#0:#{dummy_script}:2::-: ",
-          "#0:#{dummy_script}:5::-: !!",
-          "#0:#{dummy_script}:6::E: !!",
-          "#0:#{script}:11::-: dm = Dummy.new",
-          "#0:#{dummy_script}:2:Dummy:>: ",
-          "#0:#{dummy_script}:3:Dummy:-: !!",
-          "#0:#{dummy_script}:4:Dummy:<: !!",
-          "#0:#{script}:12::-: puts dm.number",
-          "135"
-        ]
-        assert_equal(expected, lines)
-        assert_empty(err)
-      end
-    end
-  end
-
-  def test_tracer_by_set_get_line_procs_with_proc
-    Dir.mktmpdir("test_ruby_tracer") do |dir|
-      dummy_script = File.join(dir, "dummy.rb")
-      open(dummy_script, "w") do |f|
-        f.print <<-'EOF'
-class Dummy
-  def initialize
-    @number = 135
-  end
-  attr :number
-end
-        EOF
-      end
-      dummy_script = File.realpath dummy_script
-      script = File.join(dir, "require_tracer.rb")
-      open(script, "w") do |f|
-        f.print <<-EOF
-require 'tracer'
-
-a_proc_to_set_get_line_procs = proc { |line|
-  str = %{\\n}
-  str = %{!!\\n} if line >= 3 and line <= 6
-  str
-}
-Tracer.set_get_line_procs('#{dummy_script}', a_proc_to_set_get_line_procs)
-Tracer.on
-require_relative 'dummy'
-
-dm = Dummy.new
-puts dm.number
-        EOF
-      end
-      assert_in_out_err([script]) do |(*lines), err|
-        expected = [
-          "#0:#{script}:10::-: require_relative 'dummy'",
-          "#0:#{dummy_script}:1::-: ",
-          "#0:#{dummy_script}:1::C: ",
-          "#0:#{dummy_script}:2::-: ",
-          "#0:#{dummy_script}:5::-: !!",
-          "#0:#{dummy_script}:6::E: !!",
-          "#0:#{script}:12::-: dm = Dummy.new",
-          "#0:#{dummy_script}:2:Dummy:>: ",
-          "#0:#{dummy_script}:3:Dummy:-: !!",
-          "#0:#{dummy_script}:4:Dummy:<: !!",
-          "#0:#{script}:13::-: puts dm.number",
-          "135"
-        ]
-        assert_equal(expected, lines)
-        assert_empty(err)
-      end
-    end
-  end
-end
diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index 8afa574ee2..56822d3329 100644
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -29,7 +29,6 @@ REPOSITORIES = {
   matrix: 'ruby/matrix',
   ostruct: 'ruby/ostruct',
   irb: 'ruby/irb',
-  tracer: 'ruby/tracer',
   forwardable: "ruby/forwardable",
   mutex_m: "ruby/mutex_m",
   racc: "ruby/racc",