Thanks for your reply.

I use pandoc/bibtex/latex to create the bibliography from the bibtex export via the mentioned CSL file.

When I use zotero to create the citation in the clipboard it is much better:

Using the Twitter Search API 2013, Documentation, Using the Twitter Search API | Twitter 
Developers, viewed 21 September 2013, <https://dev.twitter.com/docs/using-search>.

So why does pandoc/bibtex/latex creates such a different output? Afterall it uses the bibtex file from zotero and the same CSL? (I know that is not the right question for this forum, but it does puzzle me…)

Great suggestion! So I change manually @misc to @online in the bibtex file - but the reference still doesn't have the URL in it (with Elsivier).

Also, do I need another bibtex exporter, which exports webpages properly? Is there exporter repository like the CSL style repository?

@adamsmith and the Zotero export filter developers:

You are right that there is no "properly" for exporting webpages in bibtex.

However, bibtex is so limited anyway that by rights it should not be used any longer and should be replaced by biblatex instead.

In biblatex, there *is* a "properly" for exporting webpages:

@online{key1,
author = {Author, Al},
title = {Title},
date = {2011-09-14}
url = {http://webpage.url},
urldate = {2012-12-30},
}

In fact, biblatex, as opposed to bibtex, is the only database format on a par, in terms of sophistication, with the CSL database model.

biblatex is also what pandoc uses as a default if the biblio database file has a .bib extension. You can use the bibtex database format but have to indicate this by using the .bibtex extension for the database file.

The output of Zotero's "BibTeX" export filter, such as

@misc{twitter_using_2013,
type = {Documentation},
title = {Using the Twitter Search {API}},
url = {https://dev.twitter.com/docs/using-search},
urldate = {2013-09-21},
journal = {Using the Twitter Search {API} {\textbar} Twitter Developers},
month = aug,
year = {2013},
}

is broken in any case, and will, even with @misc changed to @online, neither work with bibtex (which won't understand url and urldate) nor with biblatex (which won't understand month=aug; should be month={8}).

The only half-decent way of getting online material properly formatted in bibtex, AFAIK, is to use the @misc type, put the URL in howpublished={\url{http://foo.bar}}, and, of course, load url.sty in your latex document. Still, accomodating an accessed date in bibtex is next to impossible (if you don't want to resort to the kludge of adding this to the howpublished field, that is).

What I'd recommend for Zotero is to add a working biblatex export filter, and also to fix the existing bibtex export filter to use only constructs that can actually be parsed within a bibtex environment, and to clearly point out the differences between the two export filters as well as the limitations of bibtex in the documentation.

@halloleo:

Using your biblio data, with "@misc" changed to "@online" and "month = aug" to "month = {8}", in test.bib and issuing the command

echo @twitter_using_2013 | pandoc --filter pandoc-citeproc --biblio=test.bib --csl=university-of-south-australia-harvard-2013.csl -t markdown-citations

pandoc version being 1.12.0.1, I get:

(2013)

<div class="references">

2013, Documentation, viewed 21 September 2013,
\<<https://dev.twitter.com/docs/using-search>\>.

</div>

which, though it does contain your URL, is obviously broken.

However, using the chicago-author-date style instead,

echo @twitter_using_2013 | pandoc --filter pandoc-citeproc --biblio=test.bib --csl=chicago-author-date.csl -t markdown-citations

I get:

(“Using the Twitter Search API” 2013)

<div class="references">

“Using the Twitter Search API.” 2013. Documentation. August.
<https://dev.twitter.com/docs/using-search>.

</div>

which looks more or less ok, so I'm inclined to assume that there's also an issue with university-of-south-australia-harvard-2013.csl that should be further diagnosed and fixed.

with bibtex (which won't understand url and urldate)

As adamsmith notes, many BSTs do make use of these (opcit and the babelbib libraries are examples that support the latter). Bibutils (used by citepros-hs) recognizes the URL field.

fix the existing bibtex export filter to use only constructs that can actually be parsed within a bibtex environment

BibTeX is expandable because it ignores fields not used in a BST. The downside is that people have therefore used multiple different ways to "hack" features into BibTeX. Zotero's export picks constructs that are well-documented or well-embraced (by best-of-class products like bibutils and jabref or by many BST styles).

If you're using pandoc+citeproc-hs (CSL) for your authoring, why not export to MODS XML instead of Bib(La)TeX?

MODS can have record IDs:<?xml version="1.0" encoding="UTF-8"?>
<modsCollection xmlns="http://www.loc.gov/mods/v3">
<mods ID="MY_RECORD_ID">
<titleInfo>as well as special identifiers like this:<identifier type="citekey">ref1</identifier>. When Zotero has a separate local identifier field, we should export things like this. Until then, we may want to use the mods ID anyway. And people contemplating modifying translators for pandoc may want to start with MODS, which is used natively & should export many kinds of references in a less...ambiguous?/more complete way than BibTeX.

Just to follow up:

John MacFarlane's tip to upgrade to the brand-spanking new version pandoc 1.12.0.1 made all the difference: Now pandoc has an output very similar to zotero!

Thanks for all your help!