FHIR Validator

Ensures that coded elements use values from the correct ValueSet. The validator checks the binding strength (required, extensible, preferred, example) and rejects codes that are not members of the specified expansion.

• Validates against SNOMED CT, LOINC, and RxNorm codes
• Checks for valid Coding.system and Coding.code combinations
• Supports terminology service integration for real-time code validation

Evaluates complex, cross-field business rules expressed in FHIRPath, a graph-traversal language. This goes beyond simple structure to enforce clinical logic.

• Example: Ensuring Observation.valueQuantity.unit is valid for the specific LOINC code in Observation.code
• Validates conditional logic like 'if status is final, then value must be present'
• Executes custom invariants defined in Implementation Guides

Validates a resource against a specific set of constraints defined in an Implementation Guide (IG), such as US Core or a payer-specific profile. This ensures the data is fit for a specific use case.

• Checks conformance to derived profiles beyond the base FHIR spec
• Validates slicing logic on extensions and repeated elements
• Ensures required extensions and modifier extensions are present

Validates that logical references between resources are resolvable and valid within the context of a Bundle or a server. This prevents dangling pointers in clinical data.

• Verifies that a Patient/123 reference points to an actual Patient resource
• Checks that contained resources are properly nested and referenced
• Validates version-specific references when required

The foundational process of verifying that a FHIR resource's structure strictly conforms to the StructureDefinition blueprint. A FHIR Validator parses the JSON or XML payload to ensure every element is in the correct namespace, the hierarchy is valid, and no illegal properties exist. This is the first gate—catching malformed resources before semantic checks. Without schema validation, downstream systems would crash on unexpected data shapes.

A constraint that validates the number of relationships between data elements within a FHIR resource. Cardinality rules enforce that:

• Mandatory elements (min > 0) are present, such as Patient.name
• Prohibited elements (max = 0) are absent
• Repeating elements respect upper bounds, like Observation.component A FHIR Validator rejects resources where, for example, a MedicationRequest lacks a required subject reference.

A centralized software component that a FHIR Validator calls to verify terminology bindings. When a resource element is bound to a value set like SNOMED CT or LOINC, the validator queries the terminology service to confirm the supplied code exists in the specified code system and is a member of the bound value set. This transforms syntactic validation into semantic validation, ensuring clinical codes are meaningful and interoperable.

The process of linking a data element to an unambiguous concept identifier within a formal knowledge representation. A FHIR Validator enforces required bindings by rejecting resources with codes outside the specified ontology. For extensible bindings, it raises warnings when local codes are used instead of preferred standard codes. This ensures that a Condition.code element maps to a precise SNOMED CT concept, not an ambiguous local string.

Beyond structure, semantic validation verifies that data is clinically coherent. A FHIR Validator may enforce invariants—logical rules expressed in FHIRPath—such as:

• "If Observation.status is 'final', then value must be present"
• "MedicationRequest.dosageInstruction.dose must be a positive quantity" These constraints catch nonsensical combinations that pass schema checks but violate clinical logic.

A rule-based check that verifies logical consistency across multiple fields within a single FHIR resource. Examples enforced by a FHIR Validator include:

• Ensuring Period.start is before Period.end
• Verifying that a patient's deceasedDateTime is not earlier than their birthDate
• Confirming that an AllergyIntolerance.reaction.substance is consistent with the code element These rules prevent contradictory data from entering clinical repositories.