HL7 FHIR Validation

FHIR Validation (view our FHIR Validator / Viewer here) is the process of validating an HL7 FHIR message, as to confirm that the structure and the content of the message meet defined specifications.

A few initial points:

• HL7 FHIR or “FHIR“ is the most recent digital format of healthcare data. You can read about it more here.

• HL7 FHIR has many “implementation guides“: These are *.tgz files that narrowly define the specifications of a FHIR implementation guide (“IG“). A unique implementation guide exists for different combinations of:

  • use cases (federal, prior authorization, etc.)

  • country of origin (USA, Kenya, etc.)

  • and base version (“revision”) of FHIR (R5, R4, R4.3.0, etc.)

  Implementation guides may be browsed and downloaded at simplifier.net or registry.fhir.org.

• An HL7 FHIR message can have Errors, Warnings, and Information validation notifications and still be Valid! This is true if:

  • the user is defining their own custom resource extensions - these may need to be imported into a validator if a user still wants to validate them.

  • the user is references resources not in the bundle or resource

  • newer medical codes exist that were not previously hard coded within the implementation guide

Tenasol’s FHIR Validator showing no errors with warnings and information supressed.

What is HL7 FHIR Validation?

FHIR validation seeks opportunities to make the formatting as consistent and clean to interpret as possible. Most open source validators, such as HAPI on FHIR or Inferno, break issues into Errors, Warnings, and Information. A FHIR validator does not validate unstructured fields, but most typically:

• structure (positioning and sequencing of FHIR resources/fields)

• terminology (codes)

• references (checking for empty references or reference formats)

• types of resources present

Lets go over a few examples:

A FHIR Validation Error implies there is a strict disagreement with the implementation guide specified.

A FHIR Validation Warning typically references structural un-commonalities found within your FHIR message rather than strict disagreements with the implementation guide. Your message is correct, but you might want to fix these to make it cleaner.

A FHIR Validation Information notification implies there is no issue, but an indicator of where there may an opportunity to make something that is already clean even cleaner.

Why Perform HL7 FHIR Validation?

Whenever one system is handling data to another, compiling data in FHIR can be a dynamic task that needs to be constantly monitored. Running all data through a validator before it is transmitted to another system verifies that issues are caught before they are delivered in a JSON response, so that the receiver is always getting clean data that tightly adheres to a pre-agreed upon implementation guide.

Conclusion

FHIR validation plays a vital role in maintaining data quality, ensuring interoperability, and supporting regulatory compliance in modern healthcare systems. As organizations increasingly rely on automated data exchange, the structure, codes, and references within FHIR messages must be verified to avoid downstream issues. Validators help identify inconsistencies and non-conformities early in the process, providing clarity on whether messages align with the intended implementation guide. They also offer helpful warnings and informational cues to improve message consistency—even when the message is technically valid. By routinely validating FHIR messages, teams can confidently build, test, and share health data across diverse systems, reducing costly rework and improving trust between senders and receivers. As implementation guides continue to evolve with new medical codes and country-specific use cases, validation ensures your FHIR output remains aligned with the latest standards, even in complex or custom workflows. Whether you're preparing for production deployment or testing new integrations, FHIR validation is an essential step in the process.