OpenMetrics is a specification for transmitting metrics at scale, formalizing and extending the Prometheus exposition format. It defines a standard text and protobuf representation for time-series metrics scraped by monitoring systems.
OpenMetrics
OpenMetrics is an open specification that formalizes and extends the Prometheus exposition format into a vendor-neutral standard for transmitting time-series metrics at scale. It defines exactly how a system exposes counters, gauges, histograms, and summaries so that any monitoring backend can scrape and interpret them the same way. The goal is a single, unambiguous wire format for metrics that no longer depends on one project’s implementation details.
- Prometheus lineage - It takes the widely-deployed Prometheus text format and makes it a documented standard rather than a de-facto one.
- Text and protobuf encodings - Metrics can be exposed as human-readable text or compact protobuf, covering both debuggability and efficiency.
- Typed metric families - Counters, gauges, histograms, and summaries are first-class, with explicit units and metadata attached to each series.
- Exemplars - Individual samples can carry trace references, linking a metric spike back to the specific request that caused it.
In real API operations, OpenMetrics is what a /metrics endpoint speaks so that request rates, error counts, and latency histograms can be scraped without custom adapters. Standardizing that surface means the same dashboards, alerting rules, and SLOs work across every service regardless of language or framework. Alongside OpenTelemetry, it forms the metrics half of a portable observability stack, and its exemplar support ties those metrics back to the traces that explain them.
Open source tools that implement this standard
Harvested from this standard's own governing organisation, with the license read from each repository rather than assumed. The role is what the tool does to the specification, from the shared vocabulary — so an agent holding one of these documents can resolve straight from a goal to a tool.
| Tool | Role | License | What it does |
|---|---|---|---|
| Prometheus | scrapes |
Apache-2.0 | The monitoring system and time-series database that defined the exposition format OpenMetrics standardised — scrapes metrics en... |
| Node Exporter | instruments |
Apache-2.0 | Exposes hardware and operating-system metrics from a host in the OpenMetrics format. |
| Prometheus Go Client | instruments |
Apache-2.0 | Instruments Go applications to expose metrics in the OpenMetrics exposition format. |
| Prometheus Python Client | instruments |
Apache-2.0 | Instruments Python applications to expose metrics in the OpenMetrics exposition format. |
| OpenMetrics | authors |
Apache-2.0 | The specification repository itself — the standardised exposition format for cloud-native metrics, evolved out of the Prometheu... |
| Prometheus Java Client | instruments |
Apache-2.0 | Instruments JVM applications to expose metrics in the OpenMetrics exposition format. |
