The Prometheus Custom Exporter Builder skill creates tailored Prometheus metric exporters for applications and infrastructure components that lack native Prometheus support. Using the prometheus_client Python SDK or the client_golang library, it instruments applications with counters, gauges, histograms, and summary metric types following Prometheus naming conventions and best practices. The skill configures appropriate histogram bucket boundaries based on expected value distributions for latency and size metrics. Label cardinality is carefully managed to prevent metric explosion and excessive memory consumption. Custom collectors implement the Collector interface for pulling metrics from external APIs, databases, or file-based data sources on each scrape. The skill generates proper /metrics endpoints with content negotiation supporting both text exposition format and Protocol Buffers. ServiceMonitor and PodMonitor Kubernetes custom resources are created for automatic Prometheus Operator service discovery. Recording rules and alerting rules are generated based on the exported metrics to provide immediate observability value.