Skip to content


Subversion checkout URL

You can clone with
Download ZIP
Expose Events and Metrics via HTTP and JSON
Pull request Compare This branch is 10 commits ahead, 246 commits behind boundary:master.
Fetching latest commit...
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.


Folsom is an Erlang based metrics system inspired by Coda Hale's metrics ( The metrics API's purpose is to collect realtime metrics from your Erlang applications and publish them via HTTP+JSON. folsom is not a persistent store. There are 5 types of metrics, counters, gauges, histograms (and timers), histories and meters. Metrics can be created, read, and updated via the folsom_metrics module.

Building and running

You need a (preferably recent) version of Erlang installed but that should be it.

   ./rebar get-deps
   ./rebar compile
  • Note that ibrowse is only a dep for the test suite.

folsom can be run standalone or embedded in an Erlang application.

   $ erl -pa ebin deps/*/ebin

   > folsom:start(). % or start_link ...

By default folsom will listen on localhost, port 5565 and log to 'priv/log'. All three can be adjusted by changing environment variables FOLSOM_IP, FOLSOM_PORT and FOLSOM_LOG_DIR.

Metrics API

folsom_metrics.erl is the API module you will need to use most of the time.

Retreive a list of current installed metrics:

  > folsom_metrics:get_metrics().

  $ curl http://localhost:5565/_metrics

Query a specific metric:

  > folsom_metrics:get_metric_value(Name).

  $ curl http://localhost:5565/_metrics/name

Counter metrics provide increment and decrement capabilities for a single scalar value.

  > folsom_metrics:new_counter(Name).
  > folsom_metrics:notify({Name, {inc, Value}}).
  > folsom_metrics:notify({Name, {dec, Value}}).

Gauges are point-in-time single value metrics.

  > folsom_metrics:new_gauge(Name).
  > folsom_metrics:notify({Name, Value}).
Histograms (and Timers)

Histograms are collections of values that have statistical analysis done to them, such as mean, min, max, kurtosis and percentile. The can be used like "timers" as well with the timed update functions.

  > folsom_metrics:new_histogram(Name).
  > folsom_metrics:histogram_timed_update(Name, Mod, Fun, Args).
  > folsom_metrics:histogram_timed_update(Name, Fun, Args).
  > folsom_metrics:histogram_timed_update(Name, Fun).
  > folsom_metrics:notify({Name, Value}).

Histories are a collection of past events, such as errors or log messages.

  > folsom_metrics:new_history(Name).
  > folsom_metrics:get_history_values(Name, Count). % get more than the default number of history items back
  > folsom_metrics:notify({Name, Value}).

Meters are increment only counters with mean rates and exponentially weighted moving averages applied to them, similar to a unix load average.

  > folsom_metrics:new_meter(Name).
  > folsom_metrics:notify({Name, Value}).
Erlang VM

folsom also produces Erlang VM statistics.

The result of erlang:memory/0:

   > folsom_vm_metrics:get_memory().

   $ curl http://localhost:5565/_memory

The result of erlang:system_info/1:

   > folsom_vm_metrics:get_system_info().

   $ curl http://localhost:5565/_system

The result of erlang:statistics/1:

   > folsom_vm_metrics:get_statistics().

   $ curl http://localhost:5565/_statistics

Sample Output

Stats for metric 'a':

  $ curl http://localhost:5565/_metrics/a


Results of history metric 'test':

   $ curl http://localhost:5565/_metrics/test


Erlang VM memory metrics:

   $ curl http://localhost:5565/_memory

Something went wrong with that request. Please try again.