IllegalArgumentException: metric name cannot contain whitespace when registering custom metrics

MetricRegistry Name Validation

When adding a custom metric to Dropwizard’s MetricRegistry, the framework throws IllegalArgumentException: metric name cannot contain whitespace if the supplied name includes spaces. This exception is documented in the MetricRegistry Javadoc and is also the root cause of 400 responses from the /metrics endpoint when malformed names are registered programmatically.

The goal is to expose human‑readable metric names in the /metrics output while still conforming to Prometheus label constraints, which disallow spaces. The current implementation requires manual replacement or sanitization of names before registration.

Unresolved decisions:

• Is there a built‑in mechanism or configuration option to transform or alias metric names containing spaces?
• What is the recommended strategy for mapping display names to valid Prometheus metric identifiers?
• How does the name transformation affect metric uniqueness and the ability to query metrics in Prometheus?