Legal Citation APIs
Use these APIs to analyze and query the network of citations between legal cases.
These APIs are powered by Eyecite, our tool for identifying citations in legal text. Using Eyecite, we have identified millions of citations between legal decisions.
These citations power our visualizations, tables of authorities, citation search, and more. Use this API to query this network of citations in your own research or systems.
To look up specific citations or validate that a citation is not hallucinated, see our citation lookup and verification API.
Opinions Cited/Citing API
This endpoint provides an interface into the citation graph that CourtListener provides between opinions in our case law database.
You can look up the field descriptions, filtering, ordering, and rendering options by making an OPTIONS request:
curl -v \
-X OPTIONS \
--header 'Authorization: Token <your-token-here>' \
"https://www.courtlistener.com/api/rest/v4/opinions-cited/"
That query will return the following filter options:
{
"id": {
"type": "NumberRangeFilter",
"lookup_types": [
"exact",
"gte",
"gt",
"lte",
"lt",
"range"
]
},
"citing_opinion": {
"type": "RelatedFilter",
"lookup_types": "See available filters for 'Opinions'"
},
"cited_opinion": {
"type": "RelatedFilter",
"lookup_types": "See available filters for 'Opinions'"
}
}
To understand RelatedFilters, see our query refinement documentation.
These filters allow you to filter to the opinions that an opinion cites (its "Authorities" or "backward citations") or the later opinions that cite it ("forward citations").
For example, opinion 2812209 is the decision in Obergefell v. Hodges. To see what it cites:
curl -v \
--header 'Authorization: Token <your-token-here>' \
"https://www.courtlistener.com/api/rest/v4/opinions-cited/?citing_opinion=2812209"
Which returns (in part):
{
"count": 75,
"next": "https://www.courtlistener.com/api/rest/v4/opinions-cited/?citing_opinion=2812209&cursor=cD0xMjA5NjAyMg%3D%3D",
"previous": null,
"results": [
{
"resource_uri": "https://www.courtlistener.com/api/rest/v4/opinions-cited/167909003/",
"id": 167909003,
"citing_opinion": "https://www.courtlistener.com/api/rest/v4/opinions/2812209/",
"cited_opinion": "https://www.courtlistener.com/api/rest/v4/opinions/96405/",
"depth": 1
},
{
"resource_uri": "https://www.courtlistener.com/api/rest/v4/opinions-cited/167909002/",
"id": 167909002,
"citing_opinion": "https://www.courtlistener.com/api/rest/v4/opinions/2812209/",
"cited_opinion": "https://www.courtlistener.com/api/rest/v4/opinions/2264443/",
"depth": 1
},
...
To go the other direction, and see what cites Obergefell, use the cited_opinion parameter instead:
curl -v \
--header 'Authorization: Token <your-token-here>' \
"https://www.courtlistener.com/api/rest/v4/opinions-cited/?cited_opinion=2812209"
That returns (in part):
{
"count": 403,
"next": "https://www.courtlistener.com/api/rest/v4/opinions-cited/?cited_opinion=2812209&page=2",
"previous": null,
"results": [
{
"resource_uri": "https://www.courtlistener.com/api/rest/v4/opinions-cited/213931728/",
"id": 213931728,
"citing_opinion": "https://www.courtlistener.com/api/rest/v4/opinions/10008139/",
"cited_opinion": "https://www.courtlistener.com/api/rest/v4/opinions/2812209/",
"depth": 4
},
...
Note that:
The
depthfield indicates how many times the cited opinion is referenced by the citing opinion. In the example above opinion10008139references Obergefell (2812209) four times. This may indicate that Obergefell is an important authority for10008139.Opinions are often published in more than one book or online resource. Therefore, many opinions have more than one citation to them. These are called "parallel citations." We do not have every parallel citation for every decision. This can impact the accuracy of the graph.
Bulk Data
The citation graph is exported quarterly as part of our bulk data system.
If you want to analyze the citation network, that is often the best place to begin.
mike