The FAIR principles are a recent concept so metrics are still under definition. The principles were intentionally articulated broadly but this ambiguity leads to different interpretations and the risk that metrics do not fit different community practice. The implementation of FAIR can only be achieved in an ecosystem. Research artefacts are made FAIR by the services in which they are created, discovered and reused. The FAIR principles therefore need to be applied to all components of the ecosystem, since FAIR data maturity depends on the capabilities and trustworthiness of services such as repositories and persistent identifier systems.