minItems

minItems is a validation keyword used in JSON Schema to specify the minimum number of items that an array instance must contain. It applies to array types and takes a non-negative integer value. When present, an array must have at least minItems elements to be considered valid; if the instance is not an array, the constraint does not apply unless the schema also requires type: array.

Example: a schema with { "type": "array", "minItems": 2 } will consider ["a"] and [] invalid, while ["a","b"] is valid. The keyword works in conjunction with other array-related keywords such as items, maxItems and uniqueItems. If items defines a schema for all items or separate schemas for positional items, those validations run for each element, but minItems ensures there are enough elements before those item validations are applied.

Notes: The constraint is distinct from content-based checks. minItems only counts the number of elements, not their values. If a schema uses contains with a minContains constraint, that is a separate mechanism introduced to require a minimum number of items satisfying a condition; minItems remains about total length, while minContains targets conditional matches.

Implementation considerations: JSON Schema validators generally require non-negative integers for minItems; negative values are invalid per the specification. In practice, minItems is often used to enforce non-empty arrays (minItems: 1) or to ensure a minimum list length in APIs, data models, and form validations. See also maxItems, contains, and uniqueItems for related length and content constraints.