Microsoft Compiled HTML Help

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Microsoft Compiled HTML Help
Filename extension.chm
Internet media typeapplication/[1]
Developed byMicrosoft
Initial release1997
Extended to.lit
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Microsoft Compiled HTML Help
Filename extension.chm
Internet media typeapplication/[1]
Developed byMicrosoft
Initial release1997
Extended to.lit
Microsoft Compiled HTML Help
A component of Microsoft Windows
TypeHelp system
Included withWindows 98
ReplacesMicrosoft WinHelp

Microsoft Compiled HTML Help is a Microsoft proprietary online help format, consisting of a collection of HTML pages, an index and other navigation tools. The files are compressed and deployed in a binary format with the extension .CHM, for Compiled HTML. The format is often used for software documentation.

It was introduced as the successor to Microsoft WinHelp with the release of Windows 98 and is still supported in Windows 7. Although the format was designed by Microsoft, it has been successfully reverse-engineered and is now supported in many document viewer applications.


February1996Microsoft announces plans to stop development of WinHelp and start development on HTML Help.
August1997HTML Help 1.0 (HH 1.0) is released with Internet Explorer 4.
February1998HTML Help 1.1a ships with Windows 98.
January2000HTML Help 1.3 ships with Windows 2000.
JulyHTML Help 1.32 releases with Internet Explorer 5.5 and Windows Me.
October2001HTML Help 1.33 releases with Internet Explorer 6 and Windows XP.
MarchAt the WritersUA (formerly WinWriters) conference, Microsoft announces plans for a new help platform, Help 2, which is also HTML based.
January2003Microsoft decides not to release Microsoft Help 2 as a general Help platform.

Microsoft has announced that they do not intend to add any new features to HTML Help.[2]

File format[edit]

Help is delivered as a binary file with the .chm extension. It contains a set of HTML files, a hyperlinked table of contents, and an index file. The file format has been reverse-engineered and documentation of it is freely available.[3][4]

The file starts with bytes "ITSF" (in ASCII), for "Info-Tech Storage Format".

CHM files support the following features:

Use in Windows applications[edit]

The Microsoft Reader's .lit file format is a modification of the HTML Help CHM format. CHM files are sometimes used for e-books.[6]

Sumatra PDF supports viewing CHM documents since version 1.9.

Various applications, such as HTML Help Workshop and 7-Zip can decompile CHM files. The hh.exe utility on Windows and the extract_chmLib utility (a component of chmlib) on Linux can also decompile CHM files.

Use in non-Windows applications[edit]

Read support:

Read/write support:

See also[edit]


  1. ^ Techtonik, Anatoly (11 April 2006). "application/". Retrieved 7 March 2012. 
  2. ^ "Microsoft HTML Help Downloads". Microsoft. Retrieved 6 March 2012. 
  3. ^ Wise, Paul; Wing, Jed (2005). "Unofficial (Preliminary) HTML Help Specification". Retrieved 15 August 2012. 
  4. ^ Palade, Alexandru (2005). "Archive::Chm". Retrieved 22 July 2014. 
  5. ^ "INFO: Limited Unicode Support in HTML Help". Microsoft. 11 April 2001. Retrieved 17 March 2012. 
  6. ^ Title Handbook of Data Compression Authors David Salomon, Giovanni Motta, David (CON) Bryant Edition 5, illustrated Publisher Springer, 2009 ISBN 1-84882-902-7, ISBN 978-1-84882-902-2 Length 1359 pages
  7. ^ Displaychm, KDE Service Menu

External links[edit]