newrelic-ruby-agent

The New Relic Ruby agent instruments your app and sends telemetry to New Relic's platform. It's the data collector, not the dashboard.

Apache 2.0. This is the open source agent that plugs into your Ruby app. The agent itself is free to use. What you pay for is the New Relic platform that stores, queries, and visualizes the data.

New Relic's free tier gives you 100GB of data ingestion per month, one full-platform user, and unlimited basic users. That's generous. A small Rails app's telemetry easily fits in 100GB. Paid plans start at $0.35/GB ingested beyond the free tier, plus $49/user/mo for full-platform access.

The catch: you're instrumenting your app for a proprietary SaaS platform. The agent is open source, but the value is in New Relic's platform, which is not. If New Relic changes pricing (they have before), you're locked in. For Ruby specifically, the agent adds overhead. Expect 2-5% latency impact. And the open source alternative ecosystem is strong: OpenTelemetry + Grafana gives you similar visibility without the vendor lock-in.