An open source, visual CSL editor has been developed in a collaboration of Columbia University Library and Mendeley. You can find the editor here and a usage guide here. If you have trouble editing styles you can still ask for help on the Zotero forums. You can report bugs here - make sure you're reporting reproducible errors. The github issue tracker is not the place for questions.

In many cases you may still want to manually edit CSL styles. This guide provides easy to follow steps.

Start by checking the Zotero Style Repository. If you want to improve an existing CSL style, make sure that you start from the most recent version (the repository shows the date and time each style was last updated). If you want to create a new style, find the style that most closely matches what you need using the previews in the style repository. Typically the best way to find a most similar style is the “search by Example” function of the visual style editor.

Download the style you want to edit to your computer, and open it in a (plain) text editor like Notepad on Windows, TextEdit on Mac OS X (select “Make Plain Text” under “Format”), or gedit in Linux. Other options are Notepad++ for Windows, TextWrangler for Mac OS X, oXygen XML Editor, Emacs in nXML mode, and jEdit, which all support XML syntax highlighting (CSL is an XML-based language) and in some cases also real-time validation against the CSL schema.

Paste the style code into the Zotero CSL Editor, so you instantly see the effect of code changes on the style output. If you make your edits directly in the test pane, save your edits often via your text editor or using the “Save” button , as changes in the test pane get lost easily.

See the documentation page of the CSL project website for information on making CSL changes (in particular, make sure to take a look at the CSL specification. Below we discuss a few common and simple style edits to get you started.

Important: Before installing your edited style, you must change the style title and ID at the top of the style code. If you don't change these, your modified style will be overwritten the next time the original style is updated.

The style title and ID are stored within the <title/> and <id/> elements near the top of the style. For example,

<title>American Psychological Association 6th edition</title>
<title-short>APA</title-short>
<id>http://www.zotero.org/styles/apa</id>

can be changed to

<title>American Psychological Association 6th edition Modified</title>
<title-short>APA</title-short>
<id>http://www.zotero.org/styles/apa-modified</id>

The URLs that you put in as an ID do not have to exist (i.e., you can use a zotero.org/style/mystyle type ID even if the style will not be posted on the Zotero repository).

Before installing a modified style, always make sure it is valid XML and CSL by validating against the CSL schema.

In this example, we want to display the publisher (“CSHL Press”) and the location of the publisher (“Cold Spring Harbor, NY”) in a bibliographic entry. While this can be achieved with the code

<text variable="publisher"/>
<text variable="publisher-place"/>

this would result in “CSHL PressCold Spring Harbor, NY”. Fortunately, we can add some punctuation with the prefix, suffix and delimiter attributes. Let's say we want to separate the publisher and publisher-place by a comma-space, and wrap the whole in parentheses, i.e. “(CSHL Press, Cold Spring Harbor, NY)”. This can be done with:

<group delimiter=", " prefix="(" suffix=")">
  <text variable="publisher"/>
  <text variable="publisher-place"/>
</group>

The advantage of use a group element is that whenever you have a publisher, but no publisher-place, you don't end up with incorrect punctuation: the output would become “(CSHL Press)”. If you would set the punctuation directly onto the text elements, e.g.

<text variable="publisher" prefix="("/>
<text variable="publisher-place" prefix=", " suffix=")"/>

you would lose the closing bracket, i.e. “(CSHL Press”.

There are two main settings for et-al abbreviation (e.g., rendering the names “Doe, Smith & Johnson” as “Doe et al.”). The minimum number of names that activates et-al abbreviation, and the number of names shown before “et al.”.

In CSL, these settings can appear on the style, citation, bibliography or names elements in the form of the et-al-min and et-al-use-first attributes (it is possible to have separate settings for items that have been cited previously by using the et-al-subsequent-min and et-al-subsequent-use-first attributes).

For example,

<citation et-al-min="3" et-al-use-first="1">
  ...
</citation>

will result in name lists like “Doe”, “Doe & Smith” and, if there are three or more names, “Doe et al.”. Try changing these numbers and observe the effect.

CSL offers multiple methods to disambiguate cites or names. For example, a style might normally render only the family name (e.g., “(Doe 1999, Doe 2002)”). If the authors are Jane Doe and Thomas Doe, these names can be disambiguated by adding initials or the full given names (e.g., “(J. Doe 1999, T. Doe 2002)”).

Disambiguation methods are selected on the citation element. For example, to disable given name disambiguation, delete the disambiguate-add-givenname attribute, e.g. change

<citation disambiguate-add-givenname="true">
  ...
</citation>

to

<citation>
  ...
</citation>

By default several authors are separated by a delimiter , and the word and. This settings can be changed, for example to use the symbol & instead:

<names variable="author">
  <name form="short" and="symbol" delimiter=", "/>
  ...
</names>

or to not use and at all, but to use the delimiter /:

<names variable="author">
  <name form="short" delimiter="/"/>
  ..
</names>

The appearance of citations in (full) footnote styles may depend on their position in the paper. If the same source is cited twice, it may be that a shortened version is used in the second (and any further) citation. To handle this distinction, one can use conditional rendering based on the position of the citation. A generic structure could then look as

<citation>
  <layout>
    <choose>
      <if position="ibid-with-locator">
        ...
      </if>
      <else-if position="ibid">
        ...
      </else-if>
      <else-if position="subsequent">
        ...
      </else-if>
      <else>
        ...
      </else>
    </citation>
  </layout>
</citation>

If a case is missing in your style, you can add that and fill out what and how the information should be rendered in that case (an example of such a full footnote style).

See Citation Styles.

Save the style with a “.csl” file extension (you can generally do this by simply typing ”.csl” after the name of your file). Then, go to the Cite pane in the Zotero preferences. Click on the “+” sign below the list of installed styles. In the file selection dialogue that opens, navigate to the .csl file you just created and open it. This will install your new style into the Zotero data directory.

If you think that your modified style might be useful to other people, consider submitting it to the Zotero Style Repository.

If you get stuck at any point, try posting a question on the Zotero forums.