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Note: This page is out of date and the instructions do not work with any recent version of MonoDevelop.

For an up to date guide, see Creating a Simple Add-In


MonoDevelop (and SharpDevelop) have been written so that they can be easily extended by others. This can be accomplished by doing two simple things. First, by creating an assembly (.dll) containing the code for your add-in. Second, providing an .addin XML file that maps your code into MonoDevelop. There is a detailed PDF available at SharpDevelop’s website here that you will want to read for a full understanding of the entire system and possiblities. The SharpDevelop book has information on this as well. This is intended as a simple and quick overview.


add-in What many other systems refer to as a plugin. In this case the whole application is also a plugin.
pad Content area like the project browser or output pad.
view Main content area, like the SourceEditor.
language binding Compilation, execution, and project management for a programming language.
service Reponsible for one part of the program, for example the MessageService is delegated the reponsiblity of displaying messages to the user.

Add-in assembly

In your code you can extend the IDE at pretty much any point. Some common things would be to extend the menus, pads, views, services, commands, etc. I recommend looking at src/AddIns/ for a few examples. In most cases you will simply inherit from an abstract class or implement an interface for the various parts you are extending. For example, a new service could be defined as:

 using System;
 using MonoDevelop.Core.Services;

 namespace MonoDevelop.Services;
     public class ExampleService : AbstractService
         // Do stuff here

Here is a list of some of the common classes to extend for an add-in:

.addin.xml file

Note: MonoDevelop had to change the extension to .addin.xml to use gettext in translations. SharpDevelop uses .addin.

The .addin.xml file basically maps the “entry” points of your code into the various parts of the IDE. You specify services to load, append menus in a certain place, and virtually everything else.

Since the entire application is an add-in there is no limit. It supports conditional directives and other advanced constructs. In the following sample MonoDevelopNunit.addin.xml file, you can see it specifies the name of the assembly to load, specifies a service to load into the /Workspace/Services node, two views and some menus. Lastly, it is important to note the class attribute that is used to specify the type to instantiate for that part of the add-in.

 <AddIn name        = "MonoDevelop Nunit"
        author      = "John Luke"
        copyright   = "GPL"
        url         = ""
        description = "NUnit testing tool"
        version     = "0.2">

         <Import assembly="MonoDevelop.Nunit.dll" />

     <Extension path="/Workspace/Services">
         <Class id    = "NunitService"
                class = "MonoDevelop.Services.NunitService" />

     <Extension path="/SharpDevelop/Workbench/Views">
         <Class id    = "NunitTestTree"
                class = "MonoDevelop.Nunit.Gui.TestTree" />
         <Class id    = "NunitResultTree"
                class = "MonoDevelop.Nunit.Gui.ResultTree" />

     <Extension path="/SharpDevelop/Workbench/MainMenu/Tools">
         <MenuItem id           = "NunitMenu"
                   _label       = "NUnit"
                   insertafter  = "ExternalTools"
                   insertbefore = "Options">
             <MenuItem id       = "LoadTestAssembly"
                       _label   = "Load Assembly"
                       shortcut = ""
                       class    = "MonoDevelop.Commands.NunitLoadAssembly" />

             <MenuItem id       = "NunitRunTests"
                       _label   = "Run Tests"
                       shortcut = ""
                       class    = "MonoDevelop.Commands.NunitRunTests" />

Add-in tree

The various add-ins are loaded and merged into an AddInTree, which is how the IDE knows what and where to load. Look at build/AddIns/SharpDevelopCore.addin.xml to see the various places to attach your add-in, such as the menu items.

Add-in XML format

There is an AddIn.xsd file that specifies the required/optional XML format. Perhaps someone would like to make a RelaxNG one also. See data/resources/AddIn.xsd

Building and installing

We currently support both running in a self-contained build/ directory as well as installing to $(prefix)/lib/monodevelop so you will want to make sure both your .addin.xml and .dll files are placed into the AddIn directory in both places (this this may change at some point in the future).

For those not familiar with autoconf/automake here is a brief description of what you need to do, if you are wanting to add your add-in to the current build process. This will not be required when we are self-hosting. Have a that compiles and installs your .dll and .addin.xml files. I highly recommend you copy one of the existing ones as a reference. Add path/to/your/add-in/Makefile to the AC_OUTPUT section of This creates the Makefile from In the parent directory of your add-in add your directory to the SUBDIRS variable. If you are especially prudent you can make sure make distcheck from the top directory still works.

Existing add-ins

  1. SourceEditor
  2. CSharpBinding
  3. JavaBinding
  4. NemerleBinding
  5. DebuggerAddin
  6. Monodoc
  7. StartPage (not fully ported)
  8. NUnit (incomplete)


Although SharpDevelop and MonoDevelop currently use the same format this may not always be the case. Also, while non-GUI add-ins could possibly be reused, MonoDevelop and SharpDevelop use different GUI toolkits that will likely prevent sharing many things. Any suggestions on making sharing things as easy as possible would be appreciated.


Since we are using gettext and not resources, you will want to read the translation guide as that is handled in a different way than SharpDevelop and deserves its own explanation.

Add-in ideas

There are various things that would be nice to have implemented as add-ins. Here is a brief list of the top of my head:

  1. A viewer for the Mono profiler (mono --profile) and Mono coverage tools
  2. Extra languages/compilers support
  3. NUnit and NAnt integration tools
  4. Glade (although a new GUI designer is planned)
  5. Integration with Subversion, CVS, and other version control tools
  6. UML/CASE tools
  7. SQL/database support
  8. An advanced XML editor
  9. Also, there are some additional things that SharpDevelop already has that could be ported to MonoDevelop

Credits, License, and Errata

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