Metrics for Expresser apps.

Usage no npm install needed!

<script type="module">
  import expresserMetrics from '';


Expresser Metrics

Plugin to gather and output simple metrics on Expresser apps.

Adding and using metrics

To measure something:

// Tag can be a label, or any string to differentiate requests of same metric,
// for example when requesting users, you can use the tag to define which user.
var tag = "myUser"
var metrics = require("expresser-metrics")

// Start metric of a getUserOrders call.
var mt = metrics.start("getUserOrders", tag)

// Do something here and there, for example get user orders,
// and set result as data on the metric object.
var orders = getUserOrders(tag)
mt.setData("orders", orders)

// Some more code, async, etc... then finally:

// You can also end the metric using:
// metrics.end(mt, optionalError)

Metrics cleanup

By default the module will keep all metrics data for the past 12 hours. Older data will be purged every 20 minutes automatically. Both values are customizable on the settings.

If you wish to cleanup manually, simply call:

var metrics = require("expresser-metrics")


To generate a summary about collected metrics, use the built-in output method:

var metrics = require("expresser-metrics")
var output = metrics.output()

// Some more code...


By default it will give you the specific metrics for the last 1min, 5min and 20min, having the 99, 95 and 90 percentiles. You can change these values on the settings.

You can also generate the output with your own custom options. For example to get metrics for last 1, 5, 60 and 300 minutes, and not showing the percentiles:

var options = {
    intervals: [1, 5, 60, 300],
    percentiles: []

var metrics = require("expresser-metrics")
var output = metrics.output(options)

And to get metrics for a specific call only:

function myCall() {
    var mt = metrics.start("my-call")

    // Some code, then end metrics somewhere...

var options = {
    keys: ["my-call"]

var metrics = require("expresser-metrics")
var output = metrics.output(options)

Metrics HTTP server

The Metrics module can spin up a dedicated HTTP server for the metrics output, which makes it easier for you to set firewall rules for external access.

To enable the HTTP server, simply add a valid port number to settings.metrics.httpServer.port and set settings.metrics.httpServer.autoStart to true.

If you want to control the Metrics HTTP server manually, please set the port programatically and use the start and kill methods. You can also access the underlying Express server, by using the metrics.httpServer.server object. For example:

// Some code, my app starting...

var expresser = require("expresser")
var metrics = require("expresser-metrics")

expresser.settings.metrics.httpServer.port = 8080

// Server started, add a custom route to the metrics http server
metrics.httpServer.server.get("/my-route", myRouteCallback)

// More custom stuff... now to kill:


For detailed info on specific features, check the annotated source on /docs/source/plugin.metrics.index.html