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SgmlReader is a .NET library that is handy for converting SGML content (like HTML and OFX) into well formed XML via XmlReader, XmlDocument, XDocument or XPathDocument. It runs on Windows and Linux using Mono.

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SgmlReader - Convert (almost) any HTML to valid XML

SgmlReader is a versatile C# .NET library written by Chris Lovett for parsing SGML files using the XmlReader API including HTML and OFX data. A command line utility is also provided which outputs the well formed XML result.

MindTouch uses the SgmlReader library extensively. They have also made many improvements to it.

SgmlReaderDll API

The SgmlReader is an implementation of the XmlReader API. So the only thing you really need to know is how to construct it. SgmlReader has a default constructor, then you need to set some of the properties. To load a DTD you must specify DocType="HTML" or you must provide a SystemLiteral. To specify the SGML document you must provide either the InputStream or Href. Everything else is optional. Then you can read from this reader like any other XmlReader class.

Nuget Package

This code is packaged and published at for your convenience. Using Visual Studio, Manage Nuget Packages simply search for the online package named "Microsoft.Xml.SgmlReader" add it to your project and you are good to go.

Sample Usage

// setup SgmlReader
Sgml.SgmlReader sgmlReader = new Sgml.SgmlReader()
    DocType = "HTML",
    WhitespaceHandling = WhitespaceHandling.All,
    CaseFolding = Sgml.CaseFolding.ToLower,
    InputStream = reader

// create document
XmlDocument doc = new XmlDocument()
    PreserveWhitespace = true,
    XmlResolver = null
return doc;

SgmlReader Properties

Property Name Description
SgmlDtd Dtd Specify the SgmlDtd object directly. This allows you to cache the Dtd and share it across multiple SgmlReaders. To load a DTD from a URL use the SystemLiteral property.
string DocType The name of root element specified in the DOCTYPE tag. If you specify "HTML" then the SgmlReader will use the built-in HTML DTD. In this case you do not need to specify the SystemLiteral property.
string PublicIdentifier The PUBLIC identifier in the DOCTYPE tag. This is optional.
string SystemLiteral The SYSTEM literal in the DOCTYPE tag identifying the location of the DTD.
string InternalSubset The DTD internal subset in the DOCTYPE tag. This is optional.
TextReader InputStream The input stream containing SGML data to parse. You must specify this property or the Href property before calling Read().
string Href Specify the location of the input SGML document as a URL.
string WebProxy Sometimes you need to specify a proxy server in order to load data via HTTP from outside the firewall. For example: "itgproxy:80".
string BaseUri The base Uri is used to resolve relative Uri's like the SystemLiteral and Href properties.
TextWriter ErrorLog DTD validation errors are written to this stream.
string ErrorLogFile DTD validation errors are written to this log file.

SgmlReader.exe Command Line Tool

Included in the .nuget package under the tools folder which you will find in %USERPROFILE%\.nuget\packages\microsoft.xmlsgmlreader\1.8.22\tools is a command line utility named SgmlReader.exe.


The command line executable version has the following options:

sgmlreader <options> [InputUri] [OutputFile]
Argument Name Description
-help Print the list of command-line options.
-e "file" Specifies a file to write error output to. The default is to generate no errors. Use the value "$stderr" to redirect errors to stderr.
-proxy server Specifies the proxy server to use to fetch DTDs through the firewall.
-html Specifies that the input is HTML.
-dtd "uri" Specifies some other SGML DTD.
-base Add an HTML base tag to the output.
-pretty Pretty print the output.
-encoding name Specify an encoding for the output file (default UTF-8).
-nobom Prevents the output of the BOM when using UTF-8.
-noxml Stops generation of XML declaration in output.
-doctype Copy <!DOCTYPE tag to the output.
-f Produce indented formatted output
-trimtext SGML #text nodes will be trimmed of outer whitespace.
InputUri The input file name or URL. Default is stdin. If this is a local file name then it also supports wildcards.
OutputFile The optional output file name. Default is stdout. If the InputUri contains wildcards then this just specifies the output file extension, the default being ".xml".


Converts all .htm files to corresponding .xml files using the built in HTML DTD.

sgmlreader -html *.htm *.xml

Converts all the MSN home page to XML storing the result in the local file msn.xml.

sgmlreader -html -proxy myproxy:80 msn.xml

Converts the given OFX file to XML using the SGML DTD "ofx160.dtd" specified in the test.ofx file.

sgmlreader -dtd ofx160.dtd test.ofx ofx.xml


SgmlReaderUniversal provides a custom EntityResolver named UniversalEntityResolver which allows resolving resources using the UWP Windows.Storage API's. You will need to provide this resolver by setting the Resolver property on the SgmlReader.

// setup SgmlReader
Sgml.SgmlReader sgmlReader = new Sgml.SgmlReader() {
    Resolver = new UniversalEntityResolver()


If you have questions, please post them on StackOverflow and tag them with sgmlreader. Feel free to post issues in the github issues list.

If you fix an issue, please submit PR and follow these guidelines:

Building SgmlReader

Using dotnet build

The build versioning system depends on pwsh and you can install that using:

dotnet tool install --global powershell

Now run the setup script:

pwsh -f Common/fix_versions.ps1

if this works then you can build successfully:

dotnet build SgmlReader.sln

Using MSBuild

  1. Open your Visual Studio Developer Command Prompt - or any cmd session where msbuild is in the PATH.
  2. cd <directory containing SgmlReader.sln>
  3. BUILD.cmd

The BUILD.cmd script will automatically install pwsh if necessary, run setup.ps1, restore NuGet packages, and build the solution using the default configuration.


To change the version number edit ~\Common\version.txt only and not any other file. This version will be replicated automatically to the following files using Common\fix_version.ps1:


Developer Checklist

  1. Make sure the code formatting is identical to the existing code formatting. You know that you're doing it right if your code is indistinguishable from existing code.
  • Tip: Ensure your editor uses the .editorconfig in the solution root, or customize your editor's settings to match those in the .editorconfig file.
  1. Fix any build warnings including code analysis warnings.
  2. Run the unit test to make sure no regressions are being introduced.
  3. Add a unit test to confirm your fix or feature, if needed.
  4. Submit a pull request on GitHub.


Please make sure all tests pass and new tests are added for areas you work on. See nunit. If you have Visual Studio, just open the Test Explorer and click Run All.

Signing and Publishing

To publish new nuget package run the following:

pwsh -f Common\full_sign.ps1
nuget pack SgmlReader.nuspec

Release History

Note: all 1.8.x releases up to 1.8.7 are compatible with 1.8.0. Use assembly redirection to account for newer versions when recompilation is not an option.

Release notes for 1.8.25

  • Performance improvement parsing attributes with empty values.

Release notes for 1.8.24

  • Support SGML DTD's that contain DOCTYPE tags like ofx.dtd.
  • Remove unused XmlNameTable parameter on SgmlDtd parser.
  • Adding nobom and trimtext command-line options. Improving help screen.

Release notes for 1.8.20 (2021-Feb-2)

  • Lots of code cleanups by Jason Nelson bringing the code up to stuff with lovely new C# 8 language features.

Release notes for 1.8.19 (2021-Jan-29)

  • Add direct support for .NET 5.0 version of SgmlReader.
  • Fix automated security alert in unit test project by updating log4net version.

Release notes for 1.8.16 (2020-July-24)

Thanks to Jason Nelson for the following code cleanups:

  • Makes HWStack generic to reduce casts and improve codegen
  • Inlines variable declarations
  • Uses pattern matching
  • Adds readonly annotations

Release notes for 1.8.15 (2020-Jun-1)

  • Change build system to support .NET Core 3.1 and net45, net46, net47, net48, netstandard2.0 and netstandard2.1.
  • Drop "Portable" library since this is replaced by netstandard.

Release notes for 1.8.13 (2016-Sep-27)

Release notes for 1.8.12 (2016-Sep-11)

  • Fixed NameTable so SgmlReader can be used with XPathDocument. (Chris Lovett)
  • Switched to xbuild and nunit on mono. (Chris Lovett)
  • Add portable support by adding IEntityResolver interface. (Chris Lovett)
  • Add desktop and universal implementation of IEntityResolver. (Chris Lovett)
  • Move to NUnit 3 (which no longer requires VSIX extension to run the tests). (Chris Lovett)
  • Move to Nuget 3 (multi-platform support including portable and universal apps). (Chris Lovett)

Release notes for 1.8.11 (2013-Jan-27)

  • Pulled latest psake and nuget tools. (Andy Sherwood)
  • Made sure Html.dtd was embedded as a resource in the build script for the nuget package. (Andy Sherwood)

Release notes for 1.8.10 (2013-Jan-10)

  • Fixed AttributeCount and m_state problems for use under Mono. (Max Zhao)
  • Decode unicode surrogate pairs. (CaptainCodeman)
  • Incomplete entity codes are kept intact and escaped to produce valid HTML. (Marek Stój)

Release notes for 1.8.9 (2013-Jan-09)

  • Converted license from GPL 3 to Apache 2.0.
  • Consolidated read-me files.
  • Cleaned up solution and project files.

Release notes for 1.8.8 (2011-Sep-29)

  • Converted project files to Visual Studio 2010. (Andy Sherwood)
  • Fully nugetized. Get log4net and nunit from nuget. Build nuget package with build script using psake and powershell. (Andy Sherwood)

Release notes for 1.8.7 (2010-Apr-27)

  • Provide setting to ignore DTD in parsed document (again).

Release notes for 1.8.6 (2010-Feb-19)

  • Provide setting to ignore DTD in parsed document.
  • An attribute with a missing value should be assumed to have the name of the attribute as value.
  • SgmlReader ExpandEntity with entities not ending in ';' and skips a character.
  • SgmlReader adds 65535 character at the end of the string.
  • Add test showing behavior of > char in string literals in XML.

Release notes for 1.8.5 (2009-Jul-19)

  • Unable to parse UTF-32 entities.
  • Use StringComparison.OrdinalIgnoreCase instead of StringComparison.InvariantCultureIgnoreCase.

Release notes for 1.8.4 (2009-May-19)

  • Corrupt attributes may lead to invalid attribute names, which make the produced XML unparseable.
  • Error when content contains prefixed XML processing instructions (e.g. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com🏢office" />).
  • Added -ignore flag so tests known to fail can be ignored from the suite.
  • Added test to re-parse output to make sure it's valid XML (.Net sometimes was able to generate invalid XML).

Release notes for 1.8.3 (2009-Apr-03)

  • Fixed CData section parsing skips over characters.

Release notes for 1.8.2 (2008-Nov-26)

  • Fixed regression introduced by fixing bug 5150.
  • An extra open quote/double-quote prevents the entire element from being read properly.
  • Replaced == string equality with culture invariant string.Compare().
  • Return 'null' as NameTable since none is used.
  • Added '-noformat' switch for regression tests to suppress automatic reformatting (useful for formatting tests).

Release notes for 1.8.1 (2008-Oct-08)

  • Unclosed HTML comment causes infinite loop.
  • Don't use XmlNameTable with object comparisons; it becomes unreliable after a while.

Release notes for 1.8.0 (2008-Jul-28)

BREAKING CHANGE: requires .NET 2.0

  • Major code clean-up. (thx jamesgmbutler for the contribution!)
  • Add XML-only entity &apos; to HTML DTD.

Release notes for 1.7.5 (2008-Jul-01)

  • Missing quote in attribute value causes catastrophic failure.
  • Unknown prefixes cannot be mapped to the same namespace.

Release notes for 1.7.4 (2008-Jun-03)

  • &sup2; entity is not recognized correctly.
  • Added test for entities with digits.

Release notes for 1.7.3 (2008-May-05)

  • Never close the BODY tag early (it causes loss of content).
  • Remove "<![CDATA[" inside CDATA sections.
  • Remove "]]>" inside CDATA sections.
  • Convert elements with invalid tag names into text (e.g. <>).

Release notes for 1.7.2 (2007-Dec-07)

  • Fixed bug where parsing CDATA section skipped first character.
  • Don't double parse commented out CDATA sections.
  • Added support for namespaces on elements and attributes.
  • Unknown prefixes on attributes and elements resolve to '#unknown' namespace.
  • Fix bug when parsing down-level comments, like <![if IE]>.
  • Don't allow attribute with invalid names (e.g. <p foo:="invalid" ;="bad">, etc.).

Release notes for 1.7.1 (2007-Sep-25)

  • Added 'GetLiteralEntitiesLookup()' method.
  • Fixed bugs with namespace prefixes on attributes and elements; prefixes are now stripped automatically.
  • Added SgmlReader constructor with XmlNameTable argument to avoid failed comparisons when reusing the DTD.
  • Ensured that SgmlReader is initialized identically when reusing a DTD.

Release notes for 1.7

  • Fix bug reported by chriswang - MoveToAttribute didn't save state properly.
  • Fix bug reported by starascendent - build on Visual Studio 2003 was broken.
  • Fix bug reported by sanchen - ExpandCharEntity was messed up on hex entities.
  • Fix bug reported by kojiishi - off by one bug in SniffName().
  • Fix bug reported by kojiishi - bug in loading XmlDocument from SgmlReader - this was caused by the HTML document containing an embedded <?xml version='1.0'?> declaration, so the SgmlReader now strips these.
  • Added special stripping of punctuation characters between attributes like ",".

Release notes for 1.6

  • Improve wrapping of HTML content with auto-generated <html></html> container tags.

Release notes for 1.5

  • Fix detection of ContentType=text/html and switch to HTML mode.
  • Fix problems parsing DOCTYPE tag when case folding is on.
  • Fix reading of XHTML DTD.
  • Fix parsing of content of type CDATA that resulted in the error message 'Cannot have ']]>' inside an XML CDATA block'.
  • Fix parsing of
  • Fix parsing of attributes missing the equals sign: height"4" (thanks to Ulrich Schwanitz for his fix).
  • Fix 'SniffWhitespace' thanks to "Windy Winter".
  • Added TestSuite project.

Release notes for 1.4

  • Added UserAgent string "Mozilla/4.0 (compatible;);" so that SgmlReader gets the right content from webservers.
  • Fixed handling of HTML that does not start with root <html> element tag.
  • Fixed handling of built in HTML entities.

Release notes for 1.3

  • Changed ToUpper to CaseFolding enum and added support for "auto-folding" based on input
  • Added support for <![CDATA[...]]> blocks
  • Added proper encoding support, including support for HTML <META http-equiv="content-type". This means output now has the correct XML declaration (unless you specify the new -noxml option) and any existing xml declarations in the input are stripped out so you don't end up with two.
  • Added support for ASP <%...%> blocks (thanks to Dan Whalin).
  • Now strips out DOCTYPE by default since HTML DocTypes can cause problems for XmlDocument when it tries to load the HTML DTD. but added "-doctype" switch for those who really need it to come through.
  • Fix handling of Office 2000 <?xml:namespace .../> declarations.
  • Remove bogus attributes that have no name, in cases like <class= "test">.

Release notes for 1.2

  • Converted back to Visual Studio 7.0 since this is the lowest common denominator.
  • Added ToUpper switch for upper case folding, instead of the default lower case.
  • Fix handling of UNC paths.
  • Added OFX test suite.
  • Fixed bug in parsing CDATA type elements (like <script><!-- --></script>).

Release notes for 1.1

  • Upgraded project to Visual Studio 7.1.
  • Fixed bug in accessing https authenticated sites.
  • Fixed bug in handling of content that contains nulls.
  • Improved handling of <!DOCTYPE with PUBLIC and no SYSTEM literal.
  • Fixed bug in losing attributes when auto-closing tags.
  • Fixed pretty printing output by adding WhitespaceHandling flag to SgmlReader.

Release notes for 1.0.4

  • Added -encoding option so you can change the encoding of the output file.

Release notes for

  • Implemented ReadOuterXml and ReadInnerXml and fix some bugs in dealing with xmlns attributes and dealing with non-HTML tags.

Release notes for 1.0.3

  • Fixed some CLS compliance problems with using SgmlReader from VB and a null reference exception bug when loading SgmlReader from XmlDocument.

Release notes for

  • Fixed bug in handling of encodings. Now uses the correct encoding returned from the HTTP server.

Release notes for

  • Fixed bug in handling of input that contains blank lines at the top.

Release notes for 1.0.2

  • Added fix for the way IE & Netscape deal with characters in the range 0x80 through 0x9F in HTML.

Release notes for 1.0.1

  • Fixed bug in handling of empty elements, like <INPUT>.

Release notes for 1.0

  • Add wildcard support for command line utility.

Release notes for 0.5

  • Initial release.


Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


SgmlReader is a .NET library that is handy for converting SGML content (like HTML and OFX) into well formed XML via XmlReader, XmlDocument, XDocument or XPathDocument. It runs on Windows and Linux using Mono.




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