JSON-LD

JSON-LD (JSON Linked Data) is JSON with a 
@context: a list of contexts, named by URL, that define what each field and type means. Verifiable Credentials can be written in JSON-LD.
Why it matters for credentials
Credentials come in two formats:
JSON-LD (
ldp_vc)
JWT (
jwt_vc)
Signature covers
The credential after JSON-LD processing
The JWT itself
Every field must be defined in a context
Yes
No
Issuer and verifier need the contexts
Yes, the same ones
No
For a JSON-LD credential, the signature is made over a normalized form of the credential. To make that form, the node expands every field using the contexts. A field or type that no context defines makes issuing or verifying fail.
Example: a HealthcareProviderRoleTypeCredential has the field 
roleCodeNL, which no JSON-LD context defines. Issuing it as 
ldp_vc fails; issuing it as 
jwt_vc works.
For new use cases, JWT credentials are simpler: no contexts to publish, agree on and configure.
Contexts in the Nuts node
A context URL is an identifier: a credential names it in 
@context, but it doesn't have to resolve. The Nuts node maps each URL to a copy it includes, so it never fetches these:
Context URL
Defines
https://www.w3.org/2018/credentials/v1
W3C Verifiable Credentials
https://w3c-ccg.github.io/lds-jws2020/contexts/lds-jws2020-v1.json
JsonWebSignature2020 proofs
https://w3id.org/vc/status-list/2021/v1
StatusList2021 revocation
https://schema.org
schema.org terms
https://nuts.nl/credentials/v1
NutsOrganizationCredential, NutsEmployeeCredential, NutsAuthorizationCredential, DiscoveryRegistrationCredential, NutsSelfSignedPresentation, CredentialRevocation
https://nuts.nl/credentials/2024
NutsUraCredential
A use case with its own JSON-LD credential types publishes its own context. Every node in the use case must then be configured with it: either map the context URL to a local file, or allow the node to fetch it from that URL. See Custom credential configuration in the Nuts node documentation.