Observability tools
Why the target is not scraped, and why the query returns nothing.
Prometheus fails quietly. A relabel regex is anchored at both ends, so a rule written as a substring search drops every target with nothing logged. A replace whose regex does not match changes nothing and reports nothing. A label beginning with a double underscore is discarded when relabeling finishes, so a value that was built correctly is simply absent. These tools trace what the configuration actually does, rule by rule, against the labels a target really arrives with.
Free, with no sign-up. Every one runs entirely in your browser: nothing you paste is uploaded, and there is no server to send it to.
OpenTelemetry Collector Config Validator
The exporter no pipeline references
Check how an OpenTelemetry Collector config is wired: which declared components are inert because no pipeline uses them, and whether processor order works.
PromQL Linter and Explainer
The queries that return the wrong number
Parse a PromQL query and catch what still returns a number: anchored matchers, rate outside its aggregation, and a histogram quantile over raw counters.
Prometheus Relabel Config Tester
Which rule dropped the target
Trace a Prometheus relabel_configs block rule by rule against real labels. The regex is anchored, which is why most rules do not match what you expect.