All [[supported metadata keys|00001006020000]] conform to a type.

User-defined metadata keys conform also to a type, based on the suffix of the key.
|=Suffix|=Type
|''-date''|[[Timestamp|00001006034500]]
|''-number''|[[Number|00001006033000]]
|''-role''|[[Word|00001006035500]]
|''-time''|[[Timestamp|00001006034500]]
|''-title''|[[Zettelmarkup|00001006036500]]
|''-url''|[[URL|00001006035000]]
|''-zettel''|[[Identifier|00001006032000]]
|''-zid''|[[Identifier|00001006032000]]
|''-zids''|[[IdentifierSet|00001006032500]]
|any other suffix|[[EString|00001006031500]]
The name of the metadata key is bound to the key type

Every key type has an associated validation rule to check values of the given type.
There is also a rule how values are matched, e.g. against a [[search value|00001007706000]] when selecting some zettel.
And there is a rule how values compare for sorting.
* [[Credential|00001006031000]]
* [[EString|00001006031500]]
* [[Identifier|00001006032000]]
* [[IdentifierSet|00001006032500]]
* [[Number|00001006033000]]
* [[String|00001006033500]]
* [[TagSet|00001006034000]]
* [[Timestamp|00001006034500]]
* [[URL|00001006035000]]
* [[Word|00001006035500]]
* [[Zettelmarkup|00001006036500]]