[role="xpack"]
[[dependencies]]
=== Dependencies

APM agents collect details about external calls made from instrumented services.
Sometimes, these external calls resolve into a downstream service that's instrumented -- in these cases,
you can utilize <<distributed-tracing,distributed tracing>> to drill down into problematic downstream services.
Other times, though, it's not possible to instrument a downstream dependency --
like with a database or third-party service.
**Dependencies** gives you a window into these uninstrumented, downstream dependencies.

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image::apm/images/dependencies.png[Dependencies view in the APM app in Kibana]

Many application issues are caused by slow or unresponsive downstream dependencies.
And because a single, slow dependency can significantly impact the end-user experience,
it's important to be able to quickly identify these problems and determine the root cause.

Select a dependency to see detailed latency, throughput, and failed transaction rate metrics.

[role="screenshot"]
image::apm/images/dependencies-drilldown.png[Dependencies drilldown view in the APM app in Kibana]

When viewing a dependency, consider your pattern of usage with that dependency.
If your usage pattern _hasn't_ increased or decreased,
but the experience has been negatively effected -- either with an increase in latency or errors,
there's likely a problem with the dependency that needs to be addressed.

If your usage pattern _has_ changed, the dependency view can quickly show you whether
that pattern change exists in all upstream services, or just a subset of your services.
You might then start digging into traces coming from
impacted services to determine why that pattern change has occurred.