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
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 bit 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 custom format strings in the TemplateData editor you can either type  or press the enter key to represent a newline; in either case it will display as   in the entry field.

{| class="wikitable" ! style="width:25%" | Objective ! Format string ! Output each template on its own line
 * + Examples of formats you can use
 * Inline formatting
 * Block formatting
 * No space before the parameter name,
 * Block formatting
 * No space before the parameter name,
 * Block formatting
 * No space before the parameter name,
 * No space before the parameter name,
 * No space before the parameter name,
 * No space before the parameter name,
 * Indent each parameter
 * Align all parameter names to a given length
 * Align all parameter names to a given length
 * Align all parameter names to a given length
 * Align all parameter names to a given length
 * Align all parameter names to a given length
 * Pipe characters at the end of the previous line
 * Inline style with more spaces, must be at start of line
 * Inline style with more spaces, must be at start of line
 * Inline style with more spaces, must be at start of line
 * Inline style with more spaces, must be at start of line
 * Inline style with more spaces, must be at start of line
 * Template at the start of a line, indent-aligned parameters, pipe beforehand
 * could also be written as  or.
 * could also be written as  or.

To add this information to TemplateData, you simply need to add the aliases to the parameter's information:

Auto value
You can specify an "autovalue" for a parameter. When users add the template to a page, this value will be added automatically. For example, many clean-up templates need to have the date added; if you specify an autovalue for the template's date parameter, then the date will be filled in automatically.

To add this information to TemplateData, simply add the autovalue to the parameter's information. You will probably want to use the prefix  with the values to make them stick:

Multiple parameters
If you have multiple parameters, just repeat each section (starting from the "1" tag) and fill it out as you see fit. Note that if a template has multiple parameters, you need to separate them with a comma in the templatedata, like so:

Similar parameters
When a template has multiple parameters, sometimes some of them can be of the same kind. In this case, you only need to provide full properties for the first one, and the others can "inherit" their properties from it.

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
Due to a long standing bug, users using the old wikitext editor are able to save pages which have certain types of invalid JSON, such as duplicate keys or trailing commas (details: ). However if you attempt to save this page in a Javascript based editor, such as VisualEditor or the 2017 Wikitext editor, you will see an error message "Syntax error in JSON," as the Javascript parser is stricter and doesn't allow invalid JSON. Additionally, if you attempt to open up such invalid JSON with the Template Data 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 https://jsonlint.com/, and it will highlight the problematic commas and keys so they can be removed.

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