MultiXML

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 be stuck with it, you can use MultiXML instead, which will simply choose the fastest available XML parser. Here's how to use it:

require "multi_xml"

MultiXML.parse("<tag>contents</tag>")                         #=> {"tag" => "contents"}
MultiXML.parse("<tag>contents</tag>", symbolize_names: true)  #=> {tag: "contents"}

MultiXML.parse returns {} for empty and whitespace-only inputs instead of raising, so a missing or blank payload is observable as an empty hash rather than an exception. When parsing invalid XML, MultiXML will throw a MultiXML::ParseError.

begin
  MultiXML.parse("<open></close>")
rescue MultiXML::ParseError => exception
  exception.xml    #=> "<open></close>"
  exception.cause  #=> Nokogiri::XML::SyntaxError: ...
end

Deprecated in 0.9.0

The module constant, the primary parse entry point, and the symbolize-keys option were renamed to align MultiXML with MultiJSON and Ruby stdlib JSON.parse. The old names still work in 0.x but now emit a one-time deprecation warning; they will be removed in 1.0.

Deprecated	Use instead
MultiXml (constant)	MultiXML (all-caps)
MultiXML.load(xml)	MultiXML.parse(xml)
symbolize_keys: option	symbolize_names: option

The MultiXml constant (CamelCase) continues to work as a thin delegator; every method call, constant lookup, and rescue clause routes through MultiXML transparently.

ParseError instances expose xml and cause readers. xml contains the input that caused the problem; cause contains the original exception raised by the underlying parser.

Writing a custom parser

A custom parser is any class (or module) that responds to two class methods:

class MyParser
  def self.parse(io, namespaces: :strip)
    # parse the IO-like object into a Hash, raising ParseError on failure
  end

  def self.parse_error
    MyParser::ParseError
  end
end

MultiXML.parser = MyParser

parse_error is required: MultiXML.parse rescues MyParser.parse_error to wrap parse failures in MultiXML::ParseError. The built-in parsers in lib/multi_xml/parsers/ are working examples.

MultiXML tries to have intelligent defaulting. If any supported library is already loaded, MultiXML uses it before attempting to load others. When no backend is preloaded, MultiXML walks its automatic preference list and uses the first one that loads successfully:

1. ox
2. libxml-ruby
3. nokogiri
4. oga
5. rexml

This is the library's built-in default selection order, not a guarantee that the list is globally fastest for every workload. Real-world performance depends on the document shape and the Ruby implementation, and the benchmark suite below also measures SAX backends that are not part of automatic parser detection. REXML is a Ruby default gem, so it's always available as a last-resort fallback on any supported Ruby. If you have a workload where a different backend is faster, set it explicitly with MultiXML.parser = :your_parser.

Benchmarking Parsers

This repo includes a benchmark suite that compares every available built-in backend across multiple XML shapes and sizes instead of relying on a single synthetic document. The workloads cover:

• shallow and wide XML
• deeply nested XML
• record batches with repeated siblings
• attribute-dense elements
• mixed-content sections
• namespace-heavy feeds
• a large catalog-style document

Run the full benchmark with:

bundle exec rake benchmark

You can also run the script directly for shorter runs or Markdown-friendly output:

bundle exec ruby benchmark.rb --quick
bundle exec ruby benchmark.rb --format=markdown

The output includes:

• a single best-overall parser based on the equal-weight geometric mean of per-scenario relative throughput
• an overall ranking table for every parser
• a scenario matrix showing which parser won each workload
• an exclusions table when a parser crashes or produces mismatched output on a valid workload

Allocation efficiency is reported as a secondary metric using allocated Ruby objects per parse so ties on throughput are easier to interpret.

PARSER_PREFERENCE drives auto-detection (see "Configuration" above) and is ordered fastest-first per the benchmark suite. CI re-runs the benchmark on each supported runtime and fails if the observed ranking diverges from this table:

rank	CRuby/MRI	JRuby	TruffleRuby
1	ox	—	—
2	libxml	—	rexml
3	nokogiri	nokogiri	libxml
4	oga	—	oga
5	rexml	rexml	nokogiri

A dash means the parser isn't usable on that runtime. ox has no JRuby build and is filtered out of TruffleRuby auto-detection (its SAX callbacks miscompile under the JIT after warmup); libxml-ruby has no JRuby build; oga 3.x crashes on JRuby 10 (its precompiled Java backend was built against an older JRuby API). TruffleRuby's JIT inverts the FFI-vs-pure-Ruby tradeoff for the remaining backends, so rexml rises to the top and nokogiri falls to last.

Supported Ruby Versions

This library aims to support and is tested against the following Ruby implementations:

• Ruby 3.2
• Ruby 3.3
• Ruby 3.4
• Ruby 4.0
• JRuby 10.0 (targets Ruby 3.4 compatibility)
• TruffleRuby 33.0 (native and JVM)

If something doesn't work in one of these implementations, it's a bug.

This library may inadvertently work (or seem to work) on other Ruby implementations, however support will only be provided for the versions listed above.

If you would like this library to support another Ruby version, you may volunteer to be a maintainer. Being a maintainer entails making sure all tests run and pass on that implementation. When something breaks on your implementation, you will be responsible for providing patches in a timely fashion. If critical issues for a particular implementation exist at the time of a major release, support for that Ruby version may be dropped.

Versioning

This library aims to adhere to Semantic Versioning 2.0.0. Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, that version should be immediately yanked and/or a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions. As a result of this policy, you can (and should) specify a dependency on this gem using the Pessimistic Version Constraint with two digits of precision. For example:

spec.add_dependency "multi_xml", "~> 0.9"

Copyright

Copyright (c) 2010-2026 Erik Berlin. See LICENSE for details.