Citing with Zettlr

Citing in Zettlr is done using citeproc-js, a library that works like Pandoc's citeproc-engine or Zotero. So what you see in Zettlr will match the output of Zotero's Word or LibreOffice plugins. Zettlr's citation engine has three parts: A CSL JSON or BibTex library containing all items that can be cited, a preview engine and an optional CSL stylesheet that you can use to alter the style with which your files will be exported. This guide will help you enable citations and produce beautiful looking files (not just PDF!) that contain correct and consistent citations.

Enabling Citations in Zettlr

There are two different engines that belong to the realm of citing: the previews (citations can be previewed just as images or links) and the actual process of generating citations (which happens only on export). Both of these functions are triggered by selecting a citation library that contains references. Without such a library, Zettlr will still "preview" citations (so that you can see what will trigger Pandoc's citeproc), but Zettlr won't replace the citation's contents with a generated citation.

So the first step is to create such a file. Zotero and JabRef are both recommended applications for managing your library.

To keep things simple, this tutorial assumes that you use Zotero. If you use another reference manager, please check its manual on how to export from to either CSL JSON or BibTex format.

If you use Mendeley, Citavi, EndNote, or any other references management software that does not support CSL JSON, you can use BibTex files. They will work the same way as CSL JSON files. Internally, Zettlr will convert BibTex to CSL JSON.

Step 1: Install BetterBibTex

The first step is to install the BetterBibTex plugin for Zotero. Using BetterBibTex has two important benefits over not using it. First, it keeps all of your citation keys unique across your entire library. Second, it allows you to keep your exported library file up to date so you do not have to re-export it every time something changes.

Each citation item has its own unique ID. This is necessary so that when you, for instance, realise that the publication date has been saved incorrectly, you can easily change it in Zotero and afterwards citeproc will use the corrected information. If you do not use BetterBibTex, it may happen that an ID is issued multiple times, which would either generate errors (the good way, because you know there's something wrong) or simply cause citeproc to use the first item that matches this ID (the bad way, because then you'd have to be lucky to spot the wrong citation after export).

Why is this important? For example, if you realise the publication date of a references has been saved wrong, you can change it in Zotero and citeproc will use the citation with the corrected information. However, without BetterBibTex, the same ID may be issued multiple times. This could lead to an overt error, which is good because there is actually something wrong. However, it could also lead to a silent error, where citeproc uses the first item that matches the ID; this is bad because it is hard to spot erroneous citations after export.

Tip: BetterBibTex automatically generates unique keys using an algorithm that you can customise. BetterBibTex is compatible with JabRef's citekey patterns. It will make sure that each entry is unique by optionally adding a suffix to publications which yield the same keys (e.g. you'll have something like Harvey2005a, Harvey2005b, Harvey2005c, and so forth). You can find all abilities of BetterBibTex in the plugin's extensive documentation.

Step 2: Export your library

The next step is to actually export your library. Zotero's task is to manage your references, but in order for Zettlr to be able to use them in preview as well as exported files, you need to export them into a standalone file.

We've run tests with a library containing about 700 items, and we have not experienced any performance issues exporting all of them in total.

Export your Library as Better CSL JSON

Next, click on File and select Export library …. Select Better CSL JSON as the format; if you opted to not install BetterBibTex, choose CSL JSON. By checking "Keep updated", BetterBibTex will ensure every change in Zotero will automatically update your CSL JSON file. In this way, Zettlr will always use the most up-to-date, correct citation.

If you checked "Keep updated", you can verify the status of the CSL JSON by opening the Zotero Preferences, selecting the BetterBibTex tab, and selecting Automatic Export. Here you can fine tune what is exported, and when.

Step 3: Open your library in Zettlr

Now it is time to import your library to Zettlr. To do so, open Zettlr's preferences, go to the Export tab and click the small file icon located to the right to the Citation Database input field. A dialog will appear that lets you navigate to your database file (i.e. CSL JSON or BibTex). Select your database file, save the preferences and Zettlr will automatically load the database. You are now ready to cite!

Point Zettlr to your database file

Please note that you can also add bibliography files to the defaults files. These, however, will not be loaded by Zettlr, so it will not preview any citekeys defined there.

Step 4: Enable Render Citations

In the Display section of the preferences, you will find the option Render Citations. This option has to be enabled to view formatted citations in the editor. It is enabled by default, but in case you changed that, now would be a good time to re-enable it.

Citing in Zettlr

Zettlr supports Pandoc's citeproc-syntax for writing citations. This means you will have two options to write citations. First, you can add a single ID in your text to render a citation for this ID. It should look like this: @Harvey2005a. All citation keys begin with an @ followed by the ID (i.e. BetterBibTex CiteKey).

Zettlr has an autocomplete feature that will prompt you with all available citation keys as soon as you type an @ character. If you are not presented with a list of possible references, there may be a problem with the database file (i.e. CSL JSON or BibTex) you set up previously. After you type @, you can start to type the first few characters of the ID to narrow down your search. If the reference you want to cite is at the top of the list, hit the Enter key to select it. If the reference you want is visible, but lower down the list, use the arrow keys to highlight the reference and hit the Enter key, or use your mouse to click on your reference.

Sometimes you'll want to be somewhat more specific with your citation: for example, when adding a certain page range. That is what the more extended square bracket citation is for. A citation with a so-called prefix and a page range would look like this:

[See @Harvey2005a, 45-51]

To cite multiple authors, simply divide the blocks with semicolons:

[See @Harvey2005a, 45-51; also @Ciepley2007, 8-9]

For more information on how to use citations in line with Pandoc's citeproc engine, please refer to the guide.

Please note. Zettlr's citeproc-engine is only for preview purposes. For simplicity reasons, Zettlr does not perfectly parse all citations. It is there to check that your citations are detected correctly so that you don't have missing citations on export. But be assured, Pandoc's citeproc will render the citation correctly on export.

Checking the references

After you're done citing and want to check that you've cited everything you planned to, you can open the Sidebar and switch to the references section. If something is missing from there, it's probably not been cited in your file.

Using a file-specific library

You can also use a specific bibliography file that is only used for one of your files. To do so, you must add the bibliography file to your file's YAML frontmatter. If Zettlr detects the bibliography property in a file's frontmatter, it will automatically load that file and offer you items from that file instead of your main library.


title: "My document"
tags: tag1, tag2, tag3
bibliography: ./assets/references.json

Changing the citation style

Internally, Zettlr will always use the Chicago style to render citations. Therefore, your previewed citations will always be "in-text," and never in footnote-style. This is meant as a convenience and to confirm that everything is working.

But of course you can use different citation styles, depending on either the journal requirements for which you are writing, or your personal preferences. To change the citation style Pandoc's citeproc will use to render your citations, you need to download the corresponding CSL file. A very good starting point is the Zotero style repository. There you can search for specific citation styles, preview them and download them. Another good option is the Citation Style Language styles repository

You can point Zettlr to a CSL file in two ways. First in the general preferences. In the Export tab, beneath the field for your citation database file, you can select your preferred CSL style. This will be used for all single-page exports using the toolbar button.

Second, you can set specify a CSL style for a specific project. With your project folder visible in the file manager, right-click on the project folder and select Project Settings .... Here you can specify the CSL file to use when exporting your project.

Customizing the List of References

Creating citations involves rendering the citations inside your text correctly and also collecting a list of references at the end of the document. By default, Pandoc will simply add a list of references to the end of your documents without any decoration whatsoever. But you have many options available to customize that behaviour, and knowing a few tricks can make all of your lists of references look good from the first export on.

1. Adding a Section Header

When you first export a document, you will notice that by default Pandoc will simply attach the list of references to the end of your document without any decoration – even without any title. To add a title, you can choose between two options.

The first option is to define the property reference-section-title in your file's YAML frontmatter. It accepts a string which will be set as the title for the whole section. So if you specify reference-section-title: Bibliography, Pandoc will use Bibliography as the title.

The second option is to simply end your document with the wanted heading, i.e. ## Bibliography. Pandoc will append the list of references onto the file, and if your file ends with a heading, that will become the section heading.

Obviously, it does not make sense to use both approaches, since that would yield two headings following each other.

2. Changing where the List of References Appears

Another customization option you have when using Pandoc is that you can specify where your list of references appears. For example, if you want to add another section after the list of references, such as an appendix, you will have to tell Pandoc precisely where your references should end up. For this, you need to define a div-element (which is a form of container for text) with the ID #refs. You can do so either by adding a literal HTML div, or by adding a Pandoc-internal div.

First, here's how you can define a HTML div:

Here could be the last sentence of your conclusion.

## References

<div id="refs">

## Appendix

Here you could add an appendix.

Note that in this example you should not make use of the reference-section-title YAML frontmatter since we've added a heading manually.

Here's the second example using a Pandoc div:

Here could be the last sentence of your conclusion.

## References

::: {#refs}

## Appendix

Here you could add an appendix.

You can read more on how to do this in the Pandoc manual.

3. Formatting the List of References

When you add citations to your files, you want to ensure the references are formatted neatly. If you export to Word or LibreOffice, you can fine-tune your references as you edit your file before sending it out. But this is not possible if you export to PDF. Thus you may need to add a few style directives to your file. Here we describe how to change the appearance of PDF files. To change the appearance of HTML exports, you can use CSS.

LaTeX uses lengths to determine the overall measurements of the exported PDF. These lengths are normally set globally, but they can be changed for different parts of document. One of these lengths is parindent, which controls the hanging indent of all paragraphs.

Whenever you use the command \setlength LaTeX will overwrite the specified length from wherever it encounters this command until you use \setlength again. Since the references section is formatted using paragraphs like the rest of the document, they will by default be formatted in this default style. In order to re-format the list of references to look differently, you should overwrite these just before the list of references.

The following code snippet gives you an example:

\setlength{\parindent}{-1cm} % Negative hanging indent
\setlength{\leftskip}{0.5cm} % Overall indentation
\setlength{\parskip}{0.1cm} % Spacing between paragraphs

The above example would render the reference list with a negative indent of minus one centimetre. Additionally it will apply an overall indentation of half a centimetre relative to the page margins. For example, if your left page margin is set to three centimetres, the reference list paragraphs will be offset 3.5 centimetres. The last value (parskip) controls the spacing between paragraphs, so there will be a gap of ten millimetres between paragraphs.

The above example is a good place to start. You can search for more lengths to tweak and adjust them to your liking.

Note that this mainly applies if you export your documents using the default template, or any other template that does not specifically control how citations are formatted. If you are submitting, e.g., to a STEM journal which provides its own LaTeX template and you use that one, it is likely that this already formats the list of references correctly.

Controlling Pandoc Citeproc with the YAML frontmatter

You can control certain aspects of Pandoc's citeproc using variables that can be set in your YAML frontmatter. Make sure to read the corresponding page to see, e.g., how to change the language of your references list.

Accessing a Reference's PDF From Zettlr

It will happen from time to time that you re-read something you have written and want to double-check a referenced work. You can do this by simply right-clicking a citation and opening the corresponding PDF file.

For this to work, Zotero needs to be running (since Zettlr will query the app using the citekey and ask for the actual path to the PDF file) and you need to have BetterBibTex installed (since only BetterBibTex offers the corresponding API endpoint necessary for requesting the PDF path).

Note that this does not apply for BibTex databases, since these already contain the full paths to linked PDF files (but note that these are optional, so you may need to explicitly tell your reference manager to add those paths) and as such Zettlr does not need to query an external program.