When an API or config object should allow only a fixed field set, or should allow extra keys only when their values follow one rule, express that object shape with additionalProperties and validate a short sample locally. additionalProperties:false is useful for blocking unexpected fields such as debugNote or tempFlag. additionalProperties:{type:"string"} is useful for metadata maps, env maps, and labels where extra keys are allowed but values must stay consistent.
Schema object shape and extra field topic
JSON Schema additionalProperties unknown field and object shape tools
A local workflow for additionalProperties unknown-field blocking, extra-value typing, closed-object constraints, metadata maps, and pre-release object-shape drift checks.
JSON Schema additionalPropertiesextra field validationunknown field blockingclosed object validationobject shape driftmetadata map schemaJSON Schema extra property
Common lookup scenarios
Block unknown fields in orders or config objects
Confirm a closed object only allows whitelisted fields
Require metadata or label extra values to match one type
Debug object-shape drift and leftover debug fields
Review properties, patternProperties, and extra-field rules before release
Recommended workflow
- Format the schema and JSON sample
- Use properties for fixed-field allowlists
- Set additionalProperties to false or to a value schema
- Run Schema validation and inspect keyword plus instancePath
- Use key paths, Pointer, JSONPath, and Deep Diff to trace unexpected fields
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A local workflow for additionalProperties unknown-field blocking, extra-value typing, closed-object constraints, metadata maps, and pre-release object-shape drift checks.
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LookupToolChakanFAQ
When an API or config object should allow only a fixed field set, or should allow extra keys only when their values follow one rule, express that object shape with additionalProperties and validate a short sample locally. additionalProperties:false is useful for blocking unexpected fields such as debugNote or tempFlag. additionalProperties:{type:"string"} is useful for metadata maps, env maps, and labels where extra keys are allowed but values must stay consistent.
What does additionalProperties:false block?
It rejects any extra key that is neither listed in properties nor matched by patternProperties, which is useful for fixed order, config, and API object shapes.
Why can extra-field behavior look confusing with allOf?
additionalProperties only sees properties and patternProperties in the same schema object. If your object shape is split across composed schemas, review where those fields are declared and validate with short isolated samples.
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