The [[endpoint|00001012920000]] to retrieve references of a specific zettel is ''/r/{ID}'', where ''{ID}'' is a placeholder for the [[zettel identifier|00001006050000]].

A zettel may contain references to external material, in the form of an URI.
External material may be referenced via Zettelmarkup [[links|00001007040310]], [[inline embedding|00001007040320]], or a [[block transclusion|00001007031100]].
It may also be referenced within the [[metadata|00001006000000]] of a zettel, when a key of [[type|00001006030000]] [[URL|00001006035000]] is given.

To calculate the references of a zettel, its [[parsed|00001006000000]] form is used.

For example, to retrieve references of the zettel about [[CommonMark|00001008010500]], just send an HTTP GET request to the endpoint ''/r/00001008010500''[^If [[authentication is enabled|00001010040100]], you must include a valid [[access token|00001012050200]] in the ''Authorization'' header]:
```sh
# curl 'http://127.0.0.1:23123/r/00001008010500'
https://commonmark.org/
https://commonmark.org/
https://xkcd.com/927/
https://github.github.com/gfm/
https://spec.commonmark.org/0.31.2/
https://github.com/yuin/goldmark
```

If you just want metadata external references, add a query parameter ''part=meta'':
```sh
# curl 'http://127.0.0.1:23123/r/00001008010500?part=meta'
https://commonmark.org/
```

Similarly, to retrieve only references of the zettel content, use the query parameter ''part=content'':
```sh
# curl 'http://127.0.0.1:23123/r/00001008010500?part=content'
https://commonmark.org/
https://xkcd.com/927/
https://github.github.com/gfm/
https://spec.commonmark.org/0.31.2/
https://github.com/yuin/goldmark
```

These examples illustrate that the data remains unsorted and that duplicates are preserved.
The client must handle this, e.g.:
```sh
# curl 'http://127.0.0.1:23123/r/00001008010500' | sort -u
https://commonmark.org/
https://github.com/yuin/goldmark
https://github.github.com/gfm/
https://spec.commonmark.org/0.31.2/
https://xkcd.com/927/
```

If you add the query parameter ''enc=data'', the result will be encoded as a [[symbolic expression|00001012930500]]:
```sh
# curl 'http://127.0.0.1:23123/r/00001008010500?enc=data'
("https://commonmark.org/" "https://commonmark.org/" "https://xkcd.com/927/" "https://github.github.com/gfm/" "https://spec.commonmark.org/0.31.2/" "https://github.com/yuin/goldmark")
```

Of course, you can combine the different query parameters, e.g. to retrieve an Sx list of all metadata URIs.

=== HTTP Status codes
; ''200''
: Retrieval was successful, the body contains an appropriate data value.
; ''400''
: Request was not valid.
  There are several reasons for this.
  Maybe the zettel identifier did not consist of exactly 14 digits or ''enc'' / ''part'' contained illegal values.
; ''403''
: You are not allowed to retrieve data of the given zettel.
; ''404''
: Zettel not found.
  You probably used a zettel identifier that is not used in the Zettelstore.