JSON-LD Specifications

The following document provides a specification for the JSON-LD context names used in CowCerts JSON certificates.

All specifications here extend the Blockcerts context specifications ( available in a markdown document)

And Blockcerts extends the Open Badges specifications


These are the extended JSON entities we define to achieve the digital granting of academic certificates. We also define the generic entities so that all the document can be understand within this single specifications document.


Assertions are representations of an awarded badge, used to share information about a badge belonging to one earner. Assertions are packaged for transmission as JSON objects with a set of mandatory and optional properties. Fields marked in bold letters are mandatory.

Property Expected type Description
id IRI Uniquely identifies the assertion. Should be an HTTPS dereferenceable IRI so verifiers can link to the assertion. The document behind the IRI should provide information about the assertion and its validation.
type JSON-LD type JSON-LD assertion type. The type is fixed to: Assertion.
recipient IdentityObject The recipient of the achievement.
badge BadgeClass Badge document being awarded.
verification Verification Object A collection of information allowing an inspector to verify this assertion.
issuedOn DateTime Timestamp of when the achievement was awarded. ISO 8601 compliant.
image ImageObject Image representing this achievement.
recipientProfile Recipient Profile

Blockcerts extension allowing additional recipient details including recipient’s public key to make a strong claim of the ownership over the key.

Name must be set if the verifier provided by Blockcerts has to display it.

signature MerkleProof2019 An extension that allows an issuer to issue an Open Badge on the blockchain and provide proof of inclusion in a blockchain transaction. This uses Merkle Proof Signature Suite 2019.
displayHtml Text HTML code to display the certificate Will be used in the blockcerts verifier to display the certificate visually. This way the certificate will always be visualized the same way even if the certificate displayer (in this case blockcerts verifier) changes.
issuedAt Text Place where the assertion was issued (the city for instance)
officialValidation Endorsement Mandatory field if the BagdeClass being awarded has an officiality requirement. This Endorsement has always a MinistryClaim it its claim field.
signatureLines Array of SignatureLine List of handwritten signatures that must appear in the certificate visualization
universalIdentifier Text Universal identifier of the assertion. Allows to identify the assertion uniquely in the universe. Contains a UUID string.


A collection of information about the recipient of a IdentityObject.


The Open Badges standard does not allow for a recipient to have more than one field (or a document) identifying it. For this reason, we use the government’s tax ID in this identify object and all extra fields will be placed in an additional assertion, referencing this identity object.

To provide optional additional privacy to the recipient, this field will be always hashed.

Property Expected type Description
identity IdentityHash The hash of student email.
type Property IRI

Fixed email, as Blockcerts specifies.

Extra fields will be placed in an additional endorsement.

hashed Boolean Always True.
salt Text

If the recipient is hashed, this should contain the string used to salt the hash. If this value is not provided, it should be assumed that the hash was not salted.

This field is mandatory, as opposite to the Open Badges specification.


A hash string preceded by a dollar sign (“$”) and the algorithm used to generate the hash. The supported algorithms are MD5 and SHA-256, identified by the strings md5 and sha256 respectively.


For example:


represents the result of calculating a SHA-256 hash on the string “mayze”.

For more information, see how to hash & salt in various languages.


A collection of information about a badge.

Property Expected type Description
id Text Unique IRI for the BadgeClass.
type JSON-LD type JSON-LD assertion type. The type is fixed to: BadgeClass.
name Text Name of the badge defined in the syllabus.
description Text Description of the knowledge acquired by a recipient of this badge.
image ImageObject Image representing the badge.
criteria @id:Criteria URI or embedded criteria document describing how to earn the achievement.
issuer Profile IRI or document describing the individual, entity, or organization that issued the badge.
signatureLines Array of SignatureLine List of visual signatures to display.
tags Array of Text An array containing tags that
legalText Text Additional information to the title that refers to its legality (legal text). describes the type of achievement.
official Boolean True if requires an official validation. Defaults to False if field is not present.


Metadata about images that represent Assertions, BadgeClasses or Profile.

These properties can typically be represented as just the id string of the image, but using a fleshed-out document allows for including captions and other applicable metadata. https://schema.org/ImageObject

Property Expected type Description
type JSON-LD type Type of the image object. Default is schema:ImageObject.
id IRI Data URI of the image.
caption Text Caption of the image, if any.


Descriptive metadata about the achievements necessary to be recognized with an Assertion of a particular BadgeClass.

Property Expected type Description
type JSON-LD type Type of the image object. Fixed: Criteria.
narrative Text A narrative of what is needed to earn the badge.
id IRI The URI of a webpage that describes in a human-readable format the criteria for the BadgeClass.


A Profile is a collection of information that describes the entity or organization using Open Badges.

Property Expected type Description
id IRI Issuer blockchain address IRI, defined in issuerSchema by blockcerts.
type JSON-LD type Fixed: Profile.
name Text The name of the entity or organization.
url IRI The homepage or social media profile of the entity, accessible via HTTP.
telephone Text A phone number for the entity (E.164 format).
description Text A short description of the issuer, public or private and year of creation
image ImageObject An image representing the issuer.
email Text Contact address for the individual or organization.
revocationList URI HTTP URI of the Badge Revocation List used for marking revocation of signed badges. The revocation list is published as a JSON-LD document with type RevocationList.


List of assertions revoked by the issuer of the degree.

Property Expected type Description
id IRI The id of the RevocationList.
type JSON-LD type Fixed Profile.
issuer IRI: Profile The id of the Issuer.
revokedAssertions IRI A string id identification of a badge object that has been revoked. And a string revocationReason indicate the reason for revocation.


Defined by verification property of https://w3id.org/openbadges#Assertion, with Blockcerts extensions for verification of badges on a blockchain.

Property Expected type Description.
type Array Fixed: MerkleProofVerification2017, Extension
publicKey Text Blockcerts extension: the expected blockchain address for the signer of the transaction containing the merkle proof. In Blockcerts publicKeys are typically represented with a <scheme>: prefix. For Bitcoin transactions, this would be the issuer public Bitcoin address prefixed with ecdsa-koblitz-pubkey:.


Extends the Merkle Proof 2017 verification allowing to contain additional information about the assertion: a set of endorsements. They also contain extra information to verify the certificates in other blockchains other than the ones accepted by Blockcerts (for instance, the BlockValley ones).

Some endorsements are completely optional and are signed by their issuers independently so they cannot be included inside the assertion as when signing it the signature would contain the endorsements, which as we said are optional and may appear in the future.


The signature field is the only field in an assertion that is not signed (because it contains the signature itself) therefore is the only place where these endorsements fit. They may be present or not to provide extra information about the assertion, but without them the assertion is valid.

This way we can package all information about the assertion, including its endorsements in a single portable document.

Property Expected type Description
type Array Composed type of Extension and MerkleProofVerification2019.
merkleRoot Text Batch identifier (SHA256).
targetHash Text Current document’s SHA256 hash.
anchors Array of Anchor objects Array containing a list of anchor objects that define how the merkleRoot has been registered in one or more blockchains.
proof Text See Merkle Proof 2017 for more.
endorsements Array of Endorsement Endorsements containing additional information about the current document.


Specifies how the merkleRoot in a Merkle Proof 2019 signature has been registered on a blockchain.

Property Expected type Description
type JSON-LD type BTCOpReturn or ETHData defined in https://chainpoint.org/ .
sourceId Text Identifier, such as a transaction id, used to locate anchored data.
chain Text

Chain is an optional field introduced by Blockcerts to help during verification.

Check Merkle Proof Signature 2017 specifications document to see a list of accepted chains.

otherChains Array of Other chain objects Allows to verify the certificate in other chains other than the accepted by Blockcerts. This way Blockcerts can verify with a chain they consider valid and other verifiers may supply other blockchains to verify this on too.

Other chain

Allows to define another chain where an anchor may be placed other than the accepted by the Blockcerts standard to be used by validators that both understand Blockcerts and Cowcerts standards.

Property Expected type Description
id IRI Chain id. Should be able to be dereferrenced so the document behind provides more information about the chain and how to connect to it.
name Text Commonly used name to identify the chain.
protocol Text Protocol the blockchain uses. Valid values are ETH for Ethereum.
genesis Text Hexadecimal string representing the genesis block hash for the network.
consortium IRI Consortium where the chain belongs (if any).


If the id is urn:example:local, the verifier of the certificate will connect against a local development blockchain so that blockchain checks can be triggered against a dummy blockchain.

In the case of protocol ETH, checks will be performed against a local Ethereum node using the web3 JSON-RPC at default port 8545 against the same host where the verifier is running.

A note will alert the user that the blockchain checks are performed against a dummy blockchain and must not be taken seriously.


The endorsement class is very similar to an Assertion, except that there is no defined badge property. Instead, a claim property allows endorsers to make specific claims about other Profiles, BadgeClasses, or Assertions.

Property Expected type Description
id Text Unique IRI for the endorsement instance. If using hosted verification, this should be the URI where the assertion of endorsement is accessible.
type JSON-LD type Endorsement type; Fixed: Endorsement.
claim RecipientClaim EDSClaim or MinistryClaim An entity, identified by an id and additional properties that the endorser would like to claim about that entity. Three claim entities have been defined based on the attached information.
issuer Profile The profile of the endorsement’s issuer.
issuedOn DateTime Timestamp of when the endorsement was published (ISO8601 compliant).
verification Verification Object Instructions for third parties to verify this endorsement.
signature SignatureObject An extension that allows an issuer to issue an Open Badge on the blockchain and provide proof of inclusion in a blockchain transaction. This uses Merkle Proof 2017 Signature Suite.
signatureLines Array of SignatureLine List of handwritten signatures that must appear in the certificate visualization



Appends the information of the assertion’s registry by the Education Ministry.

Property Expected type Description
type Array Composed type of MinistryClaim and Extension.
id IRI Id of the Assertion that endorsement is giving extra info.
ministrySignature SignatureLine Handwritten signature that gave validity to academic certificates analogically.
registryCode Text Alphanumeric code that represents the unique identifier of the official title record of the government of Andorra.

An extension of the information about the recipient of the assertion. Mainly uses fields from a Person

Property Expected type Description
type Array Composed type of RecipientClaim and Extension.
id IRI Id of the Assertion that endorsement is giving extra info.
givenName Text The name of the recipient
familyName Text The surnames of the recipient
birthplace Text The place where the person was born.
birthdate Text The date when the person was born.
nationality Text Nationality of the person ISO 3166-1- alpha2.
nationalId Text The national ID person of their country, e.g. the CIF/NIF in Spain or NPI in Andorra.

Adds additional information to the Assertion so it can be a valid European Diploma Supplement (EDS) .

Language codes must be compatible with BCP47. Think “en” or “es-MX”. JSON-LD allows much more expressive combinations of multiple languages in one document. It is likely that you may be able to produce Badge Objects taking advantage of these features that will not be understood by some or all validators or display tools. It is recommended to keep implementations as simple as possible and communicate with the standards group when you want to move beyond the example techniques expressed here.

It provides additional information to that included in the official degrees / diplomas and/or transcript, making it more easily understood, especially by employers or institutions outside the issuing country. (explicacio numero)

Property Expected type Description
type Array Composed type of EDSClaim and Extension.
id IRI Id of the Assertion that endorsement is giving extra info.
mainField Text 2.2 Main field(s) of study for the qualification.
awardingInstitution Text 2.3 Name (in original language) and status of awarding institution.
administeringInstitution Text 2.4 Name (in original language) and status of institution administering studies.
language Text 2.5 Language(s) of instruction / examination.
studiesLevel Text 3.1 Level of qualification.
studiesLength Text 3.2 Official length of programme.
access Text 3.3 Access requirements.
mode Text 4.1 Mode of study.
requirements Text 4.2 Programme requirements.
grades Array of EDSSubject items 4.3 Programme details.
gradingScheme Text 4.4 Grading scheme.
qualification Text 4.5 Overall classification of the qualification.
further Text 5.1 Access to further study.
competences Array of Text 5.2 Professional status and competences.
extraInfo Array of Text 6 Additional information.
educationSystem ImageObject 8 Information on the national higher education system Badge.
rectorSignature ImageObject 7 Certification of the Supplement, image of the rector signature
managerSignature ImageObject 7 Certification of the Supplement, image of the manager signature

This object includes all the information related to one subject that will be included in the European Diploma Supplement (EDS).

Property Expected type Description
name Text Name of subject
choice Text Type of the subject, it could be one of the following: OB: Obligatory; OP: Optional; LL: Free Choice
semester Text Semester during which the studies were taken
year Number Year when the subject was taken.
mobility Text International academic mobility M if was studied abroad, - if not.
grade Text Grade (CO: if convalidated) Otherwise, the grade obtained as a float. (ie: 8.4). Using a dot . as decimal separator.
credits Number Amount of ECTS credits the subject took.