Help:TemplateData/ast

 is an extension used to store information about a wikitext template and its parameters so that an editing interface can retrieve and display this information in its template editor, thus making it easier for users to add and edit templates on pages.

Since April 2019, TemplateData is part of the default user experience for all users on all Wikimedia wikis when they add a template, including unregistered users. Both the default source and visual editors incorporate it in some way. It is also used elsewhere in scripts, tools and gadgets. If you have your own wiki, you will need to install Extension:TemplateData.

Adding TemplateData to a template essentially consists of inserting a small block of JSON code (explained below) on the template's documentation page. There are two main ways you can do this, either manually or by using the TemplateData editor, a graphical user interface located on the "Edit"/"Edit source" pages of templates on wikis with the TemplateData extension installed. The JSON contains a list of parameters with info about each parameter of the template as well as the template as a whole. These are outlined below.

Once a template has TemplateData, this information will show in the user interface when a user adds the template, sometimes in place of original info or sometimes as additional info. In some cases, it may change how the editor behaves when editing or inserting the template. This can make it much easier for users to identify what they need to do with the template when adding it.

History
TemplateData was originally developed in early 2013 with in mind, which was in MediaWiki testing stages at the time. VisualEditor is the main visual editing interface for Wikimedia wikis, and TemplateData allowed it to have a more useful interface when adding templates. It was officially supported by VisualEditor immediately. As VisualEditor was rolled out to the various major Wikimedia wikis as a default feature from 2013 through 2016, TemplateData became a part of them as well.

In March 2018, Sam Wilson developed, a GUI template editor extension for the default Wikimedia source editor, (otherwise known as the 2010 wikitext editor), designed to make the process of adding templates easier by using information from TemplateData. In April 2019, TemplateWizard was made a default part of the 2010 wikitext editor on all Wikimedia wikis. This meant that TemplateData was now a default part of both the visual editor and the source editor on Wikimedia wikis.

TemplateData editor
The TemplateData editor is a tool built into the TemplateData extension for adding and editing TemplateData using a graphical user interface.

It is accessible by going to any template's page (or documentation subpage) and clicking "Edit" or "Edit source". After doing this, you will see a button above the editing area and page title that says "".



Clicking this button will enter the TemplateData editor.

The editor allows you to add template parameters and to set the most common attributes. If the page you edited already contains a block of TemplateData, then the information already documented will automatically be shown when you open the correct page in the TemplateData editor. In the first box, you can add or update a short description of the template in plain text. After that, you can use the "Add suggested parameter(s)" and "Add parameter" buttons to document the names and attributes of the parameters that the template uses.

You can list the name of the parameter, any aliases for it, the label and the description that will display to users. You can also provide an example how to use the parameter. The only required field is Name (the first field in each row), which is where you record the exact, case-sensitive name of the parameter. In the "Type" dropdown menu, you can choose the type of content that the parameter should receive, such as a string (for plain-text answers), page (for links to other pages), or dates. If the template will produce an error if this parameter is left blank, please mark it as "Required". If the parameter is commonly used or recommended, then mark it as "Suggested". The "Remove parameter information" button will delete the parameter's entry from TemplateData.



When you are finished documenting each of the parameters, click "Apply" to insert the pre-formatted TemplateData into the open editing box. You must still save the page, using the normal "Save" button underneath the editing window.

Caution: The TemplateData editor will place TemplateData on either the template page or on a documentation subpage. You determine where the TemplateData will be added by opening (editing) the page that you want the TemplateData to be placed on. However, if multiple TemplateData blocks are placed on the same template, then only one of those TemplateData blocks will be used. If there is already TemplateData on a page, then you need to edit the page where the TemplateData was previously placed to avoid accidentally creating multiple blocks of TemplateData.

Location of TemplateData
TemplateData shall be on the page it describes, or be transcluded into it. In a template, it shall typically be wrapped into tags. On normal page rendering, it displays autogenerated documentation as shown in #Example.

Structure of TemplateData
TemplateData's structure is based around the JSON standard. Note that all descriptions in TemplateData must be in plain text (no wikitext, no links, etc.).

The first thing to do is to type out a pair of  tags, anywhere on the template's documentation subpage, like so:

This tells the software that everything between the two tags is TemplateData, and should be referenced when the template is used.

Example
The descriptions inside TemplateData follow a standard layout; let's say that you have a template called "Commons" for linking to a Commons category about a topic. It takes one mandatory parameter: the name of the category on Commons. The TemplateData would look something like this:

This would display, in the template, like so:

{   "description": "A template for linking to a commons category about an article", "params": { "1": {           "label": "Commons category", "description": "The commons category you want to link to.", "default": "Category:CommonsRoot", "type": "string", "required": true }   } }

TemplateData parameters
Each parameter for TemplateData is listed below with a description and example. They are also listed at Extension:TemplateData#Format.

The order of the parameters does not affect functionality, as long as those within, for example, the  object are kept within the object.

Within the parameter's name
Note: if neither "required", "suggested" nor "deprecated" are set as true for a parameter, its status will show as "optional" in the TemplateData documentation.

Once you're done, hit "save". If you've made errors, it will not let you save (which is disruptive but means you can't break anything). Should you run into errors, explain on the feedback page what you were trying to do, and we will be happy to help.

Note that if you are abusing a hack template to dynamically generate TemplateData, it cannot be checked for errors before saving.

Note that each item of information is enclosed in quotation marks (except for  and  ) and separated from the next bit by a comma (unless it's the last one).

Effects of the type parameter
The  parameter can have multiple different effects or no effect depending on the value and depending on the template editor. Its effects are listed as follows.



The  value is intended for numerical values, including minus values and decimals.


 * In VisualEditor and the 2017 wikitext editor,  has no visible effect.
 * In the 2010 wikitext editor with TemplateWizard,,  causes the input box to display a "+" and "-" button on either side, which raise or lower a number value in the input box, respectively, and the user can only type numbers into the box. The buttons can also lower the number into negatives.



The  value is intended for any string of plain text.


 * In all main editors (VisualEditor, 2017 wikitext editor and the 2010 wikitext editor with TemplateWizard),  has no visible effect compared to.



The  value is intended for content that should be forced to stay on one line.


 * In VisualEditor and the 2017 wikitext editor,  prevents a parameter's input box from allowing new lines, which are usually possible in these editors.
 * In the 2010 wikitext editor with TemplateWizard,  has no visible effect (input boxes do not allow new lines by default in this editor).



The https:// value is intended for a URL, with Internet protocol (e.g., "https://") included.


 * In VisualEditor and the 2017 wikitext editor,  makes the input box display an external link icon (a square with arrow pointing out of it) in the left hand side of the box and makes the box glow red when the user clicks away without entering a URL value that includes a valid Internet protocol (e.g., "https://", "ftp://" or "//") followed by some text. This second effect is similar to that of the "required" setting, but it does not warn the user if they attempt to insert the template without a valid URL. It also occurs with any status setting (such as "suggested" or "deprecated").
 * In the 2010 wikitext editor with TemplateWizard,  has no visible effect.



The  value is intended for a page name on a wiki.


 * In all main editors (VisualEditor, 2017 wikitext editor and the 2010 wikitext editor with TemplateWizard),  makes the parameter input box show a suggestion dropdown menu containing a list of pages on the wiki, such as Wikipedia articles, which can be selected. Namespaces can also be defined in the search. Additionally, in VisualEditor and the 2017 wikitext editor, it forces the input box content to stay on one line. It has no other visible effect and doesn't prevent a non-page from being inputted.



The  value is intended for a file name hosted either locally on a wiki or on Wikimedia Commons.


 * In VisualEditor and the 2017 wikitext editor,  has no visible effect.
 * In the 2010 wikitext editor with TemplateWizard,  makes the parameter input box show a suggestion dropdown menu containing a list of files hosted both locally and on Wikimedia Commons, which can be selected. It also shows the thumbnail of the files. It has no other visible effect and doesn't prevent a non-file from being inputted.



The  value is intended for the name of a template.


 * In all main editors (VisualEditor, 2017 wikitext editor and the 2010 wikitext editor with TemplateWizard),  makes the parameter input box show a suggestion dropdown menu containing a list of templates, which can be selected. Additionally, in VisualEditor and the 2017 wikitext editor, it forces the input box content to stay on one line. It has no other visible effect and doesn't prevent a non-template from being inputted.



The  value is intended for a username on a wiki.


 * In all main editors (VisualEditor, 2017 wikitext editor and the 2010 wikitext editor with TemplateWizard),  makes the parameter input box show a suggestion dropdown menu containing a list of actual users' names, which can be selected. Additionally, in VisualEditor and the 2017 wikitext editor, it forces the input box content to stay on one line. It has no other visible effect and doesn't prevent a non-username from being inputted.



The  value is intended for wikitext of page content, for example, links, images or text formatting.


 * In VisualEditor and the 2017 wikitext editor,  has no visible effect.
 * In the 2010 wikitext editor with TemplateWizard,  makes the parameter input box one line taller and allows new lines, which regular input boxes in the 2010 wikitext editor do not.



The  value is intended for wikitext that cannot stand alone, i.e. it lacks an opening or closing tag or refers to other parts of wikitext.


 * In VisualEditor and the 2017 wikitext editor,  has no visible effect.
 * In the 2010 wikitext editor with TemplateWizard,  makes the parameter input box one line taller and allows new lines, which regular input boxes in the 2010 wikitext editor do not.

With other parameters


 * In VisualEditor and the 2017 wikitext editor,  overrides the visible effects of   - when both are set, the input box will not contain a URL icon nor glow red when the user clicks away without entering a valid URL.
 * In the 2010 wikitext editor with TemplateWizard,  overrides the effects of   - the value of "autovalue" will not be automatically placed in the input box if the parameter type is "number".

Custom formats
When editing the  value, you create custom formats by inputting a set of wikitext symbols using some predefined rules.


 * - start of the template
 * - content (e.g., string, integer or parameter). This underscore serves to indicate the minimum length of a value in characters and can be repeated, like . If this length is not reached, it fills the remaining characters with spaces. This can be used to align all equals signs to a specific position after a parameter (if used with   for new lines).
 * - pipe (separates parameters)
 * - equals sign (precedes the value of a parameter)
 * or pressing the enter key - new line (this will display as  in the entry field)
 * - space (can be used with  to indent new lines)
 * - end of the template

The wikitext should at least meet the minimum of, otherwise there will be an invalid format string error.

Blank boilerplate
You can copy the blank boilerplate below to add new TemplateData to a template. Only the most common tags are included.

Syntax error in JSON / Bad JSON format
This error occurs if you attempt to save TemplateData that has certain types of invalid JSON code, such as duplicate keys (parameters) or trailing/missing commas, in VisualEditor or the 2017 wikitext editor (JavaScript-based editors).

"Syntax error in JSON" shows if you attempt to save such code in VisualEditor or the 2017 wikitext editor, while "Bad JSON format" shows if you attempt to open up such code in the TemplateData GUI editor, on template pages.

This error can come up quite frequently while editing a template's TemplateData. The most common mistakes that cause this error include excess commas (such as trailing commas), missing commas and missing quotation marks.


 * Examples of trailing commas:


 * Examples of missing commas:


 * Example of missing quotation marks:

To fix these errors, you can either look for the errors in the code yourself, or you can enter the JSON block into an external JSON validator, such as JSONLint, and it will highlight the problematic commas and keys that should be removed.

Due to a longstanding bug, users using the 2010 wikitext editor are able to save pages that have such invalid JSON (details: ), as the JavaScript parser is less strict and allows invalid JSON.

Required property "paramOrder(number)" not found.
This error occurs if you state a parameter in  that is not stated in  .The number in the square brackets refers to the parameter in   that is missing. It refers to its order in the sequence, but it is one less than its actual position, since  is an array; 0 is the first one, 1 is the second, etc.

To fix this, make sure all parameters stated in  are listed in  .Alternatively, you can remove the   object to remove this error.

Invalid value for property "paramOrder(number)".
This error occurs if you state a parameter in  that is not stated in  .The number in the square brackets refers to the parameter in   that shouldn't be there. It refers to its order in the sequence, but it is one less than its actual position, since  is an array; 0 is the first one, 1 is the second, etc.

To fix this, make sure all parameters stated in  are listed in  .Alternatively, you can remove the   object to remove this error.

Property "params.parametername.required" is expected to be of type "boolean".
This error occurs if you put quotation marks around the value of either  or.

These are boolean values, not strings, therefore they require no quotation marks. To fix this, remove any quotation marks around the values  or   for these parameters.

Property "format" is expected to be ...
If the  parameter exists but its value is not ,   or a valid format string, you will see the error message "Property "format" is expected to be "inline", "block", or a valid format string."

To fix this, make sure the value after  equals   or   and that there no spelling mistakes. Alternatively, if it's wikitext, make sure it contains a minimum of  and that there are no mistakes in the syntax that would normally cause a template to fail, such as duplicate equals signs or missing/duplicate curly brackets; see the section #Custom formats for the syntax for custom formats.Alternatively, you can remove the   parameter to remove this error.

Unexpected property "parametername".
This error occurs if you state a parameter in any object that is not a parameter of that object. This may be due to spelling mistakes, or you may have written the parameter of one object under another object that it doesn't belong to.

For example, you might have written the parameter  under the root TemplateData object instead of inside  :

Alternatively, if the unexpected parameter is under a template parameter inside, you'll see its name after "params.parametername." in the error.

To fix this, make sure your parameters are in their correct location, and make sure there aren't any spelling mistakes in the parameter names. Additionally, make sure you don't state any parameters that don't exist for an object. You can check which parameters exist for an object on this page, in the section.

Required property "params" not found.
This error occurs if there is no  object in the TemplateData.This is a necessary object, as it contains all the details of each parameter, so to fix this error, make sure it's added and that there are no spelling mistakes. See the section above on how to add the  parameter.

Limitations and feedback

 * Missing features — TemplateData is an example of a tool that was made available with few features, in hope that users would help to guide development of features that they desired. If you'd like to request new features for TemplateData, please let us know.
 * Delays in showing in templates — After adding TemplateData to a template, the metadata should be visible immediately when the template is opened in the visual editor. However, it is possible that it will take several hours before the metadata will show. You can force an update by making a null edit to the template page itself (not the documentation subpage). To perform a null edit, open the template page for editing, and save the page without making any change and without adding any edit summary.
 * Current issues — A list of current bugs and feature requests is available in the Wikimedia bug tracker.

Other tools

 * : A toolbar dialog window for entering template wikitext via an form built from TemplateData.
 * TemplateData Wizard: A tool that generates TemplateData through an interactive interface.
 * Skeleton TemplateData generator: A tool that reads the source wikicode of a template, tries to find all the parameters used and outputs a skeleton document with the parameters listed.
 * JSONLint: A tool that allows you to validate manually-written JSON to help find errors in the syntax.
 * List of all templates with TemplateData on this wiki
 * With dewiki template TemplateData template data is shown in a box, and the template is added to a category of templates with template data