In this era of big data and FAIR data, data formats must be machine interpretable. XML, among other standards, satisfies this requirement. Yet many standardization initiatives cite human readability as a second, key property in data format development. Examples include the development of STAR in the field of structural biology, W3C PROV for provenance, and even the continuing development of XML. This begs the question(s), what is meant by human readability and can this property be measured for a given data format or compared between competing standards? The broad topic of readability is considered with attention to the various aspects of written text which either foster or counter readability. Drawing on efforts in the educational system, a metric is proposed for estimating the relative human readability of structured data within an archival file format. Comparison is made between the same data represented in various formats, including JSON and XML, to help judge whether these standards have accomplished their simultaneous goals of machine interpretability and human readability.