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It's a split decision.
Prometheus is an open-source metrics system you run on your own infrastructure, with local storage, PromQL, and no usage fees or imposed usage limits. Splunk is a broader data platform for security and observability, available as a cloud service or self-hosted deployment, with usage-based pricing and paid per-host observability plans. Choose Prometheus when metrics monitoring and control over deployment matter most. Choose Splunk when you need its wider security and telemetry capabilities and can budget for usage-based or host-based costs.
01Side by side
| Prometheus | Splunk | |
|---|---|---|
| Pricing model | Free; no monthly or annual fee listed | Usage-based platform plans; paid host-based observability |
| Free tier | Free open-source software, with no usage limits imposed | Free editions for Observability Cloud and Agent Observability |
| Open source and license | Open source under Apache 2.0 | Open-source status and license not stated |
| Self-hosting | Independent servers use local storage | Enterprise supports on-prem, private-cloud, and air-gapped deployment |
| API and SDKs | PromQL queries; instrumentation libraries cover most major languages | Native OpenTelemetry support, SDKs, and agents |
| Integrations | Hundreds of official and community-contributed integrations | Splunkbase lists 2,000+ integrations and apps |
| Deployment model | Self-hosted servers operate independently | Cloud, on-prem, private-cloud, or hybrid platform |
| Limits and scaling | No imposed usage limits; servers rely on local storage | Platform supports machine data at petabyte scale |
Prometheus Choose Prometheus if
- Choose Prometheus if you want free, open-source metrics monitoring.
- Choose Prometheus if PromQL fits your query and alerting workflows.
- Choose Prometheus if you want independent, self-hosted monitoring servers.
Splunk Choose Splunk if
- Choose Splunk if security and observability belong in one platform.
- Choose Splunk if you need cloud and self-hosted deployment options.
- Choose Splunk if its broader integration catalog fits your stack.
02Pricing at real usage
Prometheus is free and open source, with no seat or usage limits imposed and no monthly or annual billing listed. Your operating costs come from running the servers and local storage; the vendor does not publish a managed-service price here. Splunk Cloud Platform and Splunk Enterprise use activity-based, ingest, or workload pricing, but their prices are not published. Both list unlimited users, so the published model centers on usage rather than seat counts. Splunk Observability Cloud has a free edition; paid Infrastructure, App & Infra, and End-to-End plans list annual-billed monthly equivalents of $15, $60, and $75 per host, respectively. Those costs rise with host count. The pricing page also lists Agent Observability at $100 per 1.2 million spans per month, billed annually. Ask Splunk for a quote based on your ingest, workload, hosts, and retention needs.
03API, SDKs and integration
Prometheus centers its query and alerting workflows on PromQL. Official and community instrumentation libraries cover most major languages, and its integrations collect metrics from existing systems, including Kubernetes and other cloud and container managers. Alertmanager is a separate component for notifications and silencing. Splunk cites native OpenTelemetry support, SDKs, and agents, while Splunkbase lists more than 2,000 integrations and apps. That gives teams a wider catalog of packaged integrations, while Prometheus emphasizes metrics collection and its own query model. The product pages do not specify an API protocol, CLI, or language-by-language SDK list; confirm those details against the specific integration you plan to build. For either system, check that the required telemetry is exposed in a compatible format and that your chosen integration supports the deployment you intend to run.
04Open source, self-hosting and lock-in
Prometheus is open source under the Apache 2.0 license, with components available on GitHub. Its servers operate independently and rely on local storage, so teams can run the monitoring service themselves. Splunk's open-source status is not stated; Splunk Enterprise can run on-premises, in a private cloud, or in an air-gapped deployment, while Splunk also offers a hosted cloud platform. Both therefore have self-hosting options, but Prometheus offers a clear open-source license and Splunk Enterprise is a commercial deployment. Neither vendor publishes a specific data-export format or migration procedure on its product pages. Before adopting either, verify how you can export stored data and alert definitions. Moving between them will require mapping Prometheus metrics and PromQL rules to Splunk's data and search workflows, or the reverse.
Questions people ask
What is Prometheus used for?
Prometheus instruments, collects, stores, and queries metrics from applications, systems, and services. Teams use its dimensional time-series model and PromQL for analysis, visualizations, and alert rules. A separate Alertmanager component handles notifications and silencing.
Is Prometheus free?
Yes. Prometheus is open source under the Apache 2.0 license, with no seat or usage limits imposed and no monthly price listed. You still need to operate the servers and their local storage; the free software does not mean infrastructure has no cost.
Can Splunk be self-hosted?
Yes. Splunk Enterprise supports on-premises, private-cloud, and air-gapped deployments. Splunk also offers a cloud platform. The right option depends on where your data must live and how you plan to manage the deployment; the Enterprise plan uses usage-based pricing.
How do Prometheus and Splunk pricing compare?
Prometheus has no software usage fees. Splunk Cloud Platform and Splunk Enterprise use usage-based pricing, and their prices are not published. Splunk separately lists observability plans at $15, $60, and $75 per host per month as annual-billed equivalents, plus a free edition.