Technical definition of Add-on Libraries

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Format of Add-on library files

Add-on libraries can be shared in a .mtlib file. This file is a zip file with a specific structure and content. You can import these libraries with the File > Add On Libraries... menu option.

File / Directory name Description
library.json Configuration information for the Add-on library.
mts_properties.json Properties for macro script functions in the Add-on library.
events.json Events definition for events supported by the Add-on library.
library/ Contents of the Add-on library.
library/mtscript/ Directory containing the macro Script files for the Add-on library.
library/mtscript/public/ Directory containing the macro Script files that can be called via [macro(): ] outside of the Add-on library.
library/public/ Contents of the library that are accessible via lib:// URI but are not MTscript macros, such as JavaScript code or CSS or HTML.

Configuration File Format: library.json

  "name": "test-library",
  "version": "1.0.0",
  "website": "",
  "gitUrl": "",
  "authors": [ "RPTools Team" ],
  "license": "GPL 3.0",
  "namespace": "net.rptools.maptool.test-library",
  "description": "My new test library for stuff",
  "shortDescription": "test library",
  "allowsUriAccess": true,
  "readMeFile": "",
  "licenseFile": "license.txt",
  "requires": [
  "exports": [
Name Description Required Notes
name The name of the Add-on. Yes -
website The website for your Add-on. No -
gitUrl The url for the git source repository. No -
authors An array of the authors of the Add-on. Yes -
license The name or short description of the license. No -
namespace The namespace of the Add-on. Yes -
description The description of the Add-on. No -
shortDescription The short description of the Add-on. Yes -
allowsUriAccess Should Add-on allow URI access to contents. No -
readMeFile The path to the readme file for the Add-on. Can be plain text or GitHub-Flavored Markdown. No -
licenseFile The path to the license file for the Add-on. No -
requires An array of the Add-ons that are prerequisites (namespaces). No Added in 1.13
exports An array of directories and files that are exported to other Add-ons. No Added in 1.13

The readMeFile and licenseFile can be plain text, HTML, or GitHub-Flavored Markdown (GFM). These can be viewed from the Add-on Library dialog.

GitHub provides a way to host your own static site at If you do not have your own host, this can be used for both your Add-on website and reversed for a unique namespace. (There is no requirement for there to be an actual website running at the address used for the namespace. It's merely a unique identifier.)

Events File Format: events.json

This configuration file controls which files are executed for which events.

   "events": [
      { "name": "onFirstInit", "mts": "onFirstInit" },
      { "name": "onInit",      "mts": "onInit"},
      { "name": "onFirstInit",  "js": "/js/onFirstInit.js" },
      { "name": "onInit",       "js": "/js/onInit.js"}
   "legacyEvents": [
      { "name": "onInitiativeChangeRequest", "mts": "onInitiativeChangeRequest" },
      { "name": "onInitiativeChange",        "mts": "onInitiativeChange" },
      { "name": "onTokenMove",               "mts": "onTokenMove" },
      { "name": "onMultipleTokensMove",      "mts": "onMultipleTokensMove"}

Add-ons do not respond to the onCampaignLoad event. Instead they have 2 new events:

  • onFirstInit - This is called only once, when the Add-on is first added to the campaign. Add the same Add-on a second time (overwriting the existing one) and it will not be called again unless the Add-on is removed first.
  • onInit - This is called every time the campaign is loaded (including after the initial onFirstInit event), similar to how onCampaignLoad is called on Library Tokens. It's also called on the client when the campaign is sent to the client on the initial connection.

As of 1.13, the onFirstInit and onInit events can specify a JavaScript file to run. Unlike the MTS script, you must specify the full path to the file (the example, above, shows the JavaScript code resides in the /js directory). If you have an entry for both MTS and JavaScript, the JavaScript script will be run first, but both will be executed.

The other events must be in the legacyEvents section. As the name implies, these events are now considered to be legacy events. New events will be added in the future to replace these (these will not be removed).

Currently, only macro scripts are supported for legacyEvents; in the future, JavaScript scripts will also be supported.

MTScript macros

The library/public/ directory is only exposed via the lib:// URI if allowsUriAccess is set (see the configuration file discussion, above).

MTScript macros must all end with the file extension .mts to be recognized. Only MTScript files in library/mtscript/public/ can be called using [macro():] from outside of the Add-on. The path of the file becomes the macro name for the [macro():] call. The namespace of the Add-on library is used for the @ portion (the "location" of the macro).

Add-on libraries support both public and private macro functions. Public macro functions must reside in the library/mtscript/public/ and can be called from anywhere (chat, other Add-ons, Library Tokens, and macro buttons). You can call them using the following syntax:


The above executes the MTScript macro in the file library/mtscript/public/GetTargets.mts.

The public/ is omitted from the macro name when calling it since it has to be public to be invoked. You can also use subdirectories to organize your macros and would call them like [macro("somedir/macroname@lib:net.rptools.maptool.test-library")].

The @this shorthand can also be used for calling a macro from within the same Add-on, similar to how it works for Library Tokens. For example, [macro("mtscript2@this")].

Macro script files that are not in the public/ directory can only be called from within the Add-on itself or by events. Given a library with the namespace net.mylib.addon with the following files:




can be called from anywhere, but


can only be called from a macro (or via an triggered event) that is on the net.mylib.addon Add-on.

Since the public/ is not required, if you have two files with the same name when excluding the public/ directory component, then only the one in public/ will be able to be executed. You will not be able to call the other macro.

The above works not just with [macro():] but the other places you would expect it to as well, such as defineFunction() for user-defined functions and macro links.

JavaScript macros

JavaScript code is called differently than MTscript code.

A JavaScript file can be executed from outside the Add-on via the js.evalURI() function:

[js.evalURI(context, uri)]

This function expects a context (aka namespace) and the URI that references a file containing the JavaScript code.

The URI has the form lib://namespace/path, where namespace is the namespace of the Add-on library (as defined in its library.json configuration file), and path is the file path relative to library/public.

For instance, the file library/public/test.js inside an Add-on library with namespace net.mylib.addon can be executed as:

[js.evalURI("net.mylib.addon", "lib://net.mylib.addon/test.js")].

Any namespace can be provided as the first parameter. If it matches a namespace for an existing Add-on, then identifier lookups (for functions and variables) will be performed within that namespace first, then the global namespace. If the namespace does not match an existing Add-on, a new empty namespace is created using the given name. This latter approach may be useful if you want to fill the namespace with new JavaScript functions dynamically, rather than putting them into the Add-on. This is likely most useful when dealing with preloading data.

See public/ directory section below for more information on URIs.

Properties File Format: mts_properties.json

The mts_properties.json file contains property information about macro scripts. It is not required and currrently only allows you to set properties used in macro links.

  "properties": [ 
      "filename": "public/auto_exec.mts",
      "autoExecute": true,
      "description": "Auto executable macro link"
      "filename": "public/myUDF.mts",
      "description": "My Test UDF in a drop in lib."


  • filename - is the path of the file for the MacroScript function (excluding the mtscript/ prefix).
  • autoExecute - determines if a macro link created for this macro will be auto executable or not.
  • description - is the description that will appear in the UDF listing; unlike Library Tokens, this is just a plain string and not evaluated if it contains [].

public/ Directory

The contents of this directory are exposed as a lib:// URI as long as the allowsUriAccess is set to true in the configuration file. The public directory part of the filename is discared, for example public/myhtml.html -> lib://net.myaddons.addon1/myhtml.html.

You can add images to this directory and use src="lib://" in image tags in HTML. It will eventually work with audio (probably already does but I haven't tested it yet so I'm not claiming it will 🙂).

These assets will be included correctly in the campaign file when saving, so you do not need to add them to image tables or image tokens or any other tricks to make sure that they are included.

There are some differences to be aware of when using Library Token property support for add-ons.

The name is case sensitive, unless tokens where it is not case sensitive. The values stored do not need to be be converted to/from strings like they do with Library Tokens. In many cases related to large json values, this should result in a speed improvement. The default properties list for the campain are not present for add-ons as they are not tokens, unlike Library Tokens.

Parent topic page.