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Prometheus Alertmanager vs Riemann: catalog facts
Prometheus Alertmanager	Riemann
Free Free and open source as part of the Prometheus project.	Free Free to download and run.
Self-hosted	Linux, Self-hosted
Groups hundreds of related alerts into one notification Silencing and inhibition to cut alert noise	Low-latency stream processing of monitoring events Flexible rules written as Clojure code
Configured through files rather than a full graphical interface Designed around Prometheus and its alerting rules	Configuration requires learning Clojure syntax Keeps transient state rather than long-term storage
Downloadable app, Self-hosted	Downloadable app, Self-hosted
Open source	Closed source
License not stated	License not stated
No account needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked October 1, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.