Imported from jabrena/plinth (skills/182-java-observability-metrics-micrometer/SKILL.md). Install upstream with npx skills add jabrena/plinth --skill 182-java-observability-metrics-micrometer. Copyright stays with the author (Apache-2.0).

Java Metrics Observability with Micrometer

Implement effective Java metrics instrumentation with Micrometer by defining meaningful service-level metrics, controlling cardinality, selecting the right meter type, and exposing production-ready telemetry for dashboards and alerting.

What is covered in this Skill?

• Metrics-first observability with Micrometer in Java applications
• Meter selection: Counter, Timer, DistributionSummary, Gauge, LongTaskTimer
• Naming and tagging conventions with low-cardinality dimensions
• Cardinality and meter lifecycle safeguards to prevent time-series explosion
• Histogram/percentile strategy and SLO-oriented metrics design
• Integration guidance for Actuator + Prometheus/OpenTelemetry pipelines
• Testing and verification of metrics registration and values

Scope: Application-level metrics design and instrumentation quality for Java services, with emphasis on operationally useful and cost-efficient telemetry.

Constraints

Metrics instrumentation must be operationally safe, low-cardinality, and validated. Poor tag design or excessive meter creation can degrade observability systems and increase costs.

• LOW CARDINALITY FIRST: Never tag metrics with unbounded values (userId, UUID, raw URL, full exception message)
• RIGHT METER TYPE: Use Counter for monotonically increasing events, Timer for latency, Gauge for point-in-time state, and DistributionSummary for sampled values
• BEFORE APPLYING: Read the reference for good/bad instrumentation examples and anti-patterns
• VERIFY: Run ./mvnw clean verify or mvn clean verify after changes

When to use this skill

• Improve metrics
• Apply Micrometer
• Add metrics observability
• Refactor Micrometer instrumentation
• Add Micrometer timers counters or gauges to Java services

Workflow

1. Define measurement goals and meter contract

Identify key service indicators (throughput, latency, error ratio, saturation) and map each to stable metric names, units, and low-cardinality tags.

2. Select meter types and instrument code paths

Apply Counter/Timer/Gauge/DistributionSummary/LongTaskTimer where appropriate, ensuring consistent naming conventions and reusable tags.

3. Harden instrumentation for production

Control cardinality, avoid dynamic meter churn, configure histogram/percentile strategy only where needed, and align export settings with the telemetry backend.

4. Validate and operationalize metrics

Verify metrics in tests and runtime endpoints, confirm expected labels/units, and ensure dashboards/alerts can consume the emitted series.

Reference

For detailed guidance, examples, and constraints, see references/182-java-observability-metrics-micrometer.md.