Help:TemplateData/ast

 is a way of storing information about a wikitext template and its parameters, so that the visual editor can retrieve and display it in its template editor, thus making it easier to edit pages using that template. It is also used elsewhere in scripts, tools, and gadgets.

The TemplateData extension is installed on all wikis operated by the Wikimedia Foundation. If you have your own wiki, then you will need to install Extension:TemplateData.

TemplateData syntax allows users to write small bits of structured data to a template page, or to be transcluded into that template page (such as on a template documentation page). Once a template has this structured data, it can be displayed properly in the visual editor. While this may sound complex, it's actually very easy.

TemplateData editor
There is a built-in tool for editing TemplateData in a simpler way.

To use the TemplateData editor, go to the template's page (or its documentation subpage) and press the "Edit" button. That will give you a button that says "", just above the open editing window:

Click this button to enter the GUI tool for editing TemplateData.

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.

If the template page is protected, you can copy-and-paste the template code in the subpage, use the "Add suggested parameter(s)" button there, copy the TemplateData content, edit back the subpage to get rid of the template code and then paste the TemplateData content. To know where to paste the TemplateData content inside the subpage, you can edit TemplateData without adding anything; you can then replace the and tags and their content by pasting over them.

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.

Limitations and questions

 * 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.

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 }   } }

Description and 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.

Note that this information is current as of February 2020 and may change if new parameters are added or the template editors get updates to treat certain parameters differently or fix certain behaviours.

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).

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.

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".

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
If you attempt to save TemplateData that has certain types of invalid JSON, such as duplicate keys (parameters) or trailing/missing commas, in VisualEditor or the 2017 wikitext editor (JavaScript-based editors), you will see the error message "Syntax error in JSON". These errors can come up quite frequently while heavily editing a template's TemplateData.

Examples of trailing commas:

Examples of missing commas:

Another common cause is missing quotation marks:

Additionally, if you attempt to open up such invalid JSON with the TemplateData GUI editor, you will see the error message "Bad JSON format".

To fix these errors, 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. Alternatively, you can look for the errors in the code yourself.

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.

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 in  equals ,   or, if it's wikitext, contains a minimum of. Additionally, if it's wikitext, make sure 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.

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 is the parameter in  that is missing (it is one less, since it 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 is the parameter in the  that is missing (it is one less, since it 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.

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.

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