diff --git a/.duel.rb b/.duel.rb
new file mode 100644
index 0000000..d02a2c1
--- /dev/null
+++ b/.duel.rb
@@ -0,0 +1,11 @@
+# Duel's configuration: https://github.com/sferik/duel-ruby/blob/main/docs/configuration.md
+#
+# Duel follows conventions, so set only what differs: benchmarks are in
+# duel/**/*_duel.rb, each version's lib/ is first on the load path, a
+# change is compared when it touches lib/ or ext/, and releases are
+# tagged v*.
+Duel.configure do |c|
+  # The library each version's workers require (from the gemspec, unless
+  # this says otherwise).
+  # c.library = "multi_xml"
+end
diff --git a/.github/workflows/perf.yml b/.github/workflows/perf.yml
new file mode 100644
index 0000000..22ffbe0
--- /dev/null
+++ b/.github/workflows/perf.yml
@@ -0,0 +1,64 @@
+name: Perf
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+  schedule:
+    - cron: "0 4 * * *"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: write # to comment on a pull request with the report
+
+jobs:
+  duel:
+    name: Duel
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0 # the baseline comes from history, tags included
+      # (And whatever else your tests need set up: packages, services.)
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "3.4"
+          bundler-cache: true
+      # Against the main branch for a pull request, what was there before
+      # for a push, and the last release on a schedule (slow creep). Duel
+      # adds its report to the job's summary, and writes it to duel.md for
+      # the comment.
+      - name: Compare
+        env:
+          DUEL_BASE: ${{ github.event_name == 'schedule' && 'last-release' || github.event_name == 'push' && github.event.before || '' }}
+          # (Run by hand, it compares anyway: with nothing changed, the code
+          # with itself, which checks the setup.)
+          DUEL_FORCE: ${{ github.event_name == 'workflow_dispatch' && '1' || '' }}
+        run: |
+          # (A branch's first push, or one that rewrote history, has no
+          # commit before it here to compare against.)
+          if [ "$GITHUB_EVENT_NAME" = push ] && ! git cat-file -e "$DUEL_BASE^{commit}" 2>/dev/null; then
+            echo "::notice::No commit before this push to compare against"
+            exit 0
+          fi
+          bundle exec duel --markdown "$RUNNER_TEMP/duel.md"
+      # The report, as a comment on the pull request: one comment, updated
+      # on every push. (A pull request from a fork gets no comment, as its
+      # token can't write one: the job's summary has the report.)
+      - name: Comment on the pull request
+        if: ${{ !cancelled() && github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name == github.repository }}
+        env:
+          GH_TOKEN: ${{ github.token }}
+          PR: ${{ github.event.pull_request.number }}
+        run: |
+          [ -f "$RUNNER_TEMP/duel.md" ] || exit 0
+          marker="<!-- duel -->"
+          { echo "$marker"; cat "$RUNNER_TEMP/duel.md"; } > "$RUNNER_TEMP/comment.md"
+          ids=$(gh api --paginate "repos/$GITHUB_REPOSITORY/issues/$PR/comments" \
+            --jq ".[] | select(.user.login == \"github-actions[bot]\" and (.body | startswith(\"$marker\"))) | .id")
+          if [ -n "$ids" ]; then
+            gh api --method PATCH "repos/$GITHUB_REPOSITORY/issues/comments/${ids%%$'\n'*}" -F body=@"$RUNNER_TEMP/comment.md" > /dev/null
+          else
+            gh api --method POST "repos/$GITHUB_REPOSITORY/issues/$PR/comments" -F body=@"$RUNNER_TEMP/comment.md" > /dev/null
+          fi
diff --git a/.gitignore b/.gitignore
index 991df23..310dbaf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,4 @@ doc/*
 log/*
 measurement/*
 pkg/*
+tmp/*
diff --git a/.rubocop.yml b/.rubocop.yml
index 057479a..c9de647 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -7,8 +7,14 @@ plugins:
   - rubocop-minitest
   - standard-performance
 
+inherit_mode:
+  merge:
+    - Include
+
 AllCops:
   NewCops: enable
+  Include:
+    - .duel.rb
   TargetRubyVersion: 3.2
 
 Layout/ArgumentAlignment:
diff --git a/Gemfile b/Gemfile
index c28e1cf..1317e14 100644
--- a/Gemfile
+++ b/Gemfile
@@ -28,4 +28,10 @@ gem "steep", ">= 2", platforms: :ruby
 gem "yard", ">= 0.9.38"
 gem "yardstick", ">= 0.9.9"
 
+group :development do
+  # Duel requires Ruby 3.4 or later
+  gem "duel" if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.4")
+  gem "stackprof", platforms: :mri
+end
+
 gemspec
diff --git a/README.md b/README.md
index f50ef7b..2b883d2 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,7 @@
 [![Typecheck](https://github.com/sferik/multi_xml/actions/workflows/typecheck.yml/badge.svg)][typecheck]
 [![Docs](https://github.com/sferik/multi_xml/actions/workflows/docs.yml/badge.svg)][docs]
 [![Gem Version](https://badge.fury.io/rb/multi_xml.svg)][gem]
+[![Duel](https://raw.githubusercontent.com/sferik/duel-ruby/main/assets/badge.svg)](https://github.com/sferik/duel-ruby)
 
 Lots of Ruby libraries parse XML and everyone has their favorite XML parser.
 Instead of choosing a single XML parser and forcing users of your library to
diff --git a/Rakefile b/Rakefile
index 50ed4f6..329493d 100644
--- a/Rakefile
+++ b/Rakefile
@@ -66,3 +66,10 @@ default_tasks = %i[test lint verify_measurements mutant]
 default_tasks << :steep unless RUBY_PLATFORM == "java" || Gem.win_platform?
 
 task default: default_tasks
+
+begin
+  require "duel/rake_task"
+  Duel::RakeTask.new
+rescue LoadError
+  # Duel requires Ruby 3.4 or later
+end
diff --git a/duel/backend_duel.rb b/duel/backend_duel.rb
new file mode 100644
index 0000000..cd13ab8
--- /dev/null
+++ b/duel/backend_duel.rb
@@ -0,0 +1,22 @@
+# The same 20 records through each of the other backends, picked per
+# call with the :parser option. The backend's module is resolved once,
+# untimed, so each iteration times only the parse and the hash-building
+# that MultiXML's own handler for that backend does.
+require_relative "duel_helper"
+
+{
+  "libxml" => :libxml,
+  "libxml SAX" => :libxml_sax,
+  "nokogiri" => :nokogiri,
+  "nokogiri SAX" => :nokogiri_sax,
+  "oga" => :oga,
+  "rexml" => :rexml
+}.each do |label, name|
+  duel "backend: #{label}, 20 records" do
+    once do
+      @parser = MultiXML.with_parser(name) { MultiXML.parser }
+      MultiXML.parse(@xml = record_document(20), parser: @parser)
+    end
+    MultiXML.parse(@xml, parser: @parser)
+  end
+end
diff --git a/duel/boot_duel.rb b/duel/boot_duel.rb
new file mode 100644
index 0000000..7ccb8d5
--- /dev/null
+++ b/duel/boot_duel.rb
@@ -0,0 +1,3 @@
+# How long the library takes to load, with its standard-library
+# dependencies (bigdecimal, date, time, and yaml).
+duel_process "boot: require multi_xml", ruby: %(require "multi_xml")
diff --git a/duel/duel_helper.rb b/duel/duel_helper.rb
new file mode 100644
index 0000000..4263a17
--- /dev/null
+++ b/duel/duel_helper.rb
@@ -0,0 +1,104 @@
+# Shared XML documents for the benchmarks. Every document is built from
+# fixed inputs, so each iteration and each version parses the same bytes.
+# The shapes follow the payloads in benchmark.rb.
+
+# Auto-detection picks the first parser library already loaded, so which
+# one a worker gets would depend on whether a backend benchmark loaded
+# LibXML or Nokogiri before the first parse. Pin Ox, the one detection
+# prefers, so every worker of both versions parses with the same backend.
+MultiXML.parser = :ox
+
+def token(prefix, index, width)
+  base = "#{prefix}_#{index.to_s(36)}_abcdefghijklmnopqrstuvwxyz0123456789"
+  (base * (width.to_f / base.length).ceil)[0, width]
+end
+
+def timestamp(index)
+  Kernel.format("2026-04-%<day>02dT12:%<minute>02d:56Z", day: (index % 28) + 1, minute: index % 60)
+end
+
+def wrap_root(inner) = "<root>#{inner}</root>"
+
+def tiny_document = "<user><name>Erik</name><active>yes</active></user>"
+
+def shallow_document(count)
+  wrap_root(Array.new(count) { |i| "<field#{i}>#{token("node", i, 24)}</field#{i}>" }.join)
+end
+
+def deep_document(depth)
+  open_tags = Array.new(depth) { |i| %(<level#{i} depth="#{i}"><value>#{token("value", i, 24)}</value>) }
+  wrap_root(open_tags.join + Array.new(depth) { |i| "</level#{depth - 1 - i}>" }.join)
+end
+
+def record(index)
+  status = (index % 3).zero? ? "active" : "pending"
+  amount = Kernel.format("%.2f", ((index * 17) % 10_000) / 10.0)
+  %(<record id="#{index}"><title>#{token("title", index, 40)}</title><status>#{status}</status>) +
+    "<created_at>#{timestamp(index)}</created_at><amount>#{amount}</amount>" \
+    "<tags><tag>alpha</tag><tag>beta</tag><tag>#{token("tag", index, 12)}</tag></tags></record>"
+end
+
+def record_document(count) = wrap_root(Array.new(count) { |i| record(i) }.join)
+
+def attribute_document(count)
+  nodes = Array.new(count) do |i|
+    attrs = Array.new(8) { |slot| %(a#{slot}="#{token("attr", i + slot, 14)}") }.join(" ")
+    "<node #{attrs}>#{token("node", i, 18)}</node>"
+  end
+  wrap_root(nodes.join)
+end
+
+def mixed_document(count)
+  sections = Array.new(count) do |i|
+    %(<section id="s#{i}"><title>#{token("title", i, 28)}</title>) +
+      "<p>This #{token("text", i, 18)} text has <em>inline emphasis #{i}</em> and <strong>strong #{i}</strong>.</p>" \
+      "<p>#{token("body", i + 1, 46)} <a href=\"https://example.test/#{i}\">link #{i}</a> #{token("tail", i + 2, 20)}</p></section>"
+  end
+  wrap_root(sections.join)
+end
+
+def feed_document(count)
+  entries = Array.new(count) do |i|
+    %(<atom:entry gd:id="item-#{i}" ex:version="#{i}"><atom:title>#{token("title", i, 34)}</atom:title>) +
+      %(<atom:content type="text">#{token("content", i, 58)}</atom:content><gd:rating value="#{(i % 5) + 1}"/>) +
+      %(<ex:metadata ex:region="us-west-2" ex:trace="trace-#{i}"/></atom:entry>)
+  end
+  namespaces = %(xmlns:atom="http://www.w3.org/2005/Atom" xmlns:gd="http://schemas.google.com/g/2005" xmlns:ex="https://example.test/schema")
+  %(<atom:feed #{namespaces}>#{entries.join}</atom:feed>)
+end
+
+def product(index)
+  [
+    %(<product sku="sku-#{index}" region="us" updated="#{timestamp(index)}"><name>#{token("name", index, 30)}</name>),
+    %(<price currency="USD">#{Kernel.format("%.2f", ((index * 13) % 100_000) / 100.0)}</price>),
+    %(<inventory available="#{index % 2}" warehouse="w#{index % 11}">#{(index * 7) % 400}</inventory>),
+    "<categories><category>hardware</category><category>component</category>",
+    "<category>#{token("category", index, 12)}</category></categories>",
+    product_dimensions(index),
+    "<description>#{token("description", index, 120)}</description></product>"
+  ].join
+end
+
+def product_dimensions(index)
+  "<dimensions><width>#{(index % 100) + 1}</width><height>#{(index % 80) + 1}</height><depth>#{(index % 50) + 1}</depth></dimensions>"
+end
+
+def catalog_document(count) = wrap_root(Array.new(count) { |i| product(i) }.join)
+
+# Records whose values carry type attributes, as Rails' to_xml writes
+# them, so that typecasting converts every one.
+def typed_record(index)
+  [
+    %(<user><id type="integer">#{index}</id><name>#{token("name", index, 20)}</name>),
+    %(<score type="float">#{index}.5</score><balance type="decimal">#{index}.25</balance>),
+    %(<admin type="boolean">#{index.even?}</admin><born-on type="date">2001-02-#{(index % 28) + 1}</born-on>),
+    %(<updated-at type="dateTime">#{timestamp(index)}</updated-at><nickname nil="true"/>),
+    %(<roles type="array"><role>reader</role><role>writer</role></roles></user>)
+  ].join
+end
+
+def typed_document(count) = %(<users type="array">#{Array.new(count) { |i| typed_record(i) }.join}</users>)
+
+def dashed_document(count)
+  wrap_root(Array.new(count) { |i| "<first-name-#{i}>#{token("first", i, 16)}</first-name-#{i}>" }.join)
+end
diff --git a/duel/parse_duel.rb b/duel/parse_duel.rb
new file mode 100644
index 0000000..57a8b5d
--- /dev/null
+++ b/duel/parse_duel.rb
@@ -0,0 +1,76 @@
+# MultiXML.parse with the default parser (Ox, pinned in duel_helper.rb)
+# and default options: typecasting on, and namespaces stripped. Each
+# document is built and parsed once, untimed, so the parser is detected
+# and loaded before anything is measured.
+require_relative "duel_helper"
+
+duel "parse: a tiny document" do
+  once { MultiXML.parse(@xml = tiny_document) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: 10 records" do
+  once { MultiXML.parse(@xml = record_document(10)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: 120 records" do
+  once { MultiXML.parse(@xml = record_document(120)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: a large catalog" do
+  once { MultiXML.parse(@xml = catalog_document(100)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: 450 shallow fields" do
+  once { MultiXML.parse(@xml = shallow_document(450)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: a tree 180 levels deep" do
+  once { MultiXML.parse(@xml = deep_document(180)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: attribute-dense nodes" do
+  once { MultiXML.parse(@xml = attribute_document(100)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: mixed content" do
+  once { MultiXML.parse(@xml = mixed_document(60)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: a feed, namespaces stripped" do
+  once { MultiXML.parse(@xml = feed_document(60)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: a feed, namespaces preserved" do
+  once { MultiXML.parse(@xml = feed_document(60), namespaces: :preserve) }
+  MultiXML.parse(@xml, namespaces: :preserve)
+end
+
+duel "parse: dashed keys" do
+  once { MultiXML.parse(@xml = dashed_document(100)) }
+  MultiXML.parse(@xml)
+end
+
+duel "parse: 120 records, symbolized names" do
+  once { MultiXML.parse(@xml = record_document(120), symbolize_names: true) }
+  MultiXML.parse(@xml, symbolize_names: true)
+end
+
+duel "parse: 120 records, no typecasting" do
+  once { MultiXML.parse(@xml = record_document(120), typecast_xml_value: false) }
+  MultiXML.parse(@xml, typecast_xml_value: false)
+end
+
+duel "parse: 10 records from an IO" do
+  once { MultiXML.parse(@io = StringIO.new(record_document(10))) }
+  @io.rewind
+  MultiXML.parse(@io)
+end
diff --git a/duel/typecast_duel.rb b/duel/typecast_duel.rb
new file mode 100644
index 0000000..98242ba
--- /dev/null
+++ b/duel/typecast_duel.rb
@@ -0,0 +1,13 @@
+# Typecasting values by their type attributes (integer, float, decimal,
+# boolean, date, dateTime, nil, and array), as Rails' to_xml writes them.
+require_relative "duel_helper"
+
+duel "typecast: one typed record" do
+  once { MultiXML.parse(@xml = typed_document(1)) }
+  MultiXML.parse(@xml)
+end
+
+duel "typecast: 50 typed records" do
+  once { MultiXML.parse(@xml = typed_document(50)) }
+  MultiXML.parse(@xml)
+end
diff --git a/multi_xml.gemspec b/multi_xml.gemspec
index 6dff6a0..af43ae4 100644
--- a/multi_xml.gemspec
+++ b/multi_xml.gemspec
@@ -26,7 +26,7 @@ Gem::Specification.new do |spec|
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
   spec.files = Dir.chdir(__dir__) do
     `git ls-files -z`.split("\x0").reject do |f|
-      (File.expand_path(f) == __FILE__) || f.start_with?(*%w[bin/ test/ spec/ features/ .git .circleci appveyor])
+      (File.expand_path(f) == __FILE__) || f.start_with?(*%w[bin/ test/ spec/ features/ duel/ .duel.rb .git .circleci appveyor])
     end
   end
   spec.bindir = "exe"