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11.0.0 • Public • Published


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Prometheus metrics exporter for Fastify.

This plugin uses prom-client under the hood.

This plugin also adds two http metrics for your routes:

  • Requests duration histogram
  • Requests duration summary


Fastify support

  • v3.x.x - supports fastify-1.x
  • v4.x.x - supports fastify-2.x prom-client-11.x
  • v5.x.x - supports fastify-2.x prom-client-12.x
  • v6.x.x - supports fastify-3.x
  • v9.x.x - supports fastify-4.x prom-client-14.x

Notable changes


  • Replace route context.config with routeConfig due to deprecation in fastify v4 and removal in fastify v5. If you had disableMetrics option in you route config, update fastify to latest version.
  • Prefer request.routeOptions.method over deprecated request.routerMethod.


  • Fastify v4 support.
  • Complete config rewrite, default behaviour changed.
  • Support disabling metrics in route config.
  • Now collects metrics only for registered routes by default.
  • Unknown routes metrics collection disabled by default.
  • Removed metrics from request. Now it uses WeakMap and not exposed.
  • Add balcklisting possibility for request methods.
  • Registry overrides moved to metric configuration.
  • Support overriding all Summary and Histogram options for default route metrics.


  • Fastify v3 support.
  • Drop node.js 8 support.
  • enableDefaultMetrics - now enables only default prom-client metrics. Set to true by default.
  • enableRouteMetrics - additional flag that enables route metrics. Set to true by default.


npm i fastify-metrics --save
pnpm i fastify-metrics --save

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Features and requirements

  • Collects default server metrics (see prom-client);
  • Collects route response timings
  • Adds metrics to fastify instance for your custom metrics.

  • Requires fastify >=4.0.0.
  • Node.js >=18.0.0.

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Add it to your project like regular fastify plugin. Use register method and pass options to it.

const fastify = require('fastify');
const app = fastify();

const metricsPlugin = require('fastify-metrics');
await app.register(metricsPlugin, { endpoint: '/metrics' });

It also exports client to fastify instance fastify.metrics.client which you may use it in your routes.

You may create your metrics when app starts and store it in fastify.metrics object and reuse them in multiple routes.

Registry clear

After calling registry.clear() all metrics are removed from registry. In order to add them again to the registry, call fastify.mterics.initMetricsInRegistry.

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Plugin options

See for details docs

Property Type Default Value
defaultMetrics? IDefaultMetricsConfig { enabled: true }
endpoint? string | null | Fastify.RouteOptions '/metrics'
name? string 'metrics'
routeMetrics? IRouteMetricsConfig { enabled: true }
promClient? prom-client instance | null null

Route metrics

Property Type Default Value
enabled? boolean | { histogram: boolean, summary: boolean } true
enableSummaries? boolean true
groupStatusCodes? boolean false
invalidRouteGroup? string '__unknown__'
methodBlacklist? readonly string[] ['HEAD','OPTIONS','TRACE','CONNECT',]
overrides? IRouteMetricsOverrides
registeredRoutesOnly? boolean true
customLabels? Record<string, string | ((request: FastifyRequest, reply: FastifyReply) => string)> undefined
routeBlacklist? readonly (string | RegExp)[] []

Route metrics enabled

The enabled configuration option can be either a boolean which enables/disables generation of both histograms and summaries, or it can be set to an object that allows you to pick individually whether you want histograms or summaries to be generated, for example:

  routeMetrics: {
    enabled: {
      histogram: true,
      summary: false

would result in the library only generating histograms.

Route metrics overrides

You may override default metrics settings. You may provide overrides for two metrics tracking http request durations: histogram and summary.

const fastify = require('fastify');
const app = fastify();
const metricsPlugin = require('fastify-metrics');

await app.register(metricsPlugin, {
  endpoint: '/metrics',
  routeMetrics: {
    overrides: {
      histogram: {
        name: 'my_custom_http_request_duration_seconds',
        buckets: [0.1, 0.5, 1, 3, 5],
      summary: {
        help: 'custom request duration in seconds summary help',
        labelNames: ['status_code', 'method', 'route'],
        percentiles: [0.5, 0.75, 0.9, 0.95, 0.99],
Property Type Default value
getRouteLabel? (request: FastifyRequest) => string undefined
method? string 'method'
route? string 'route'
status? string 'status_code'
Request durations summary
Property Type Default value
name? string 'http_request_summary_seconds'
help? string 'request duration in seconds summary'
percentiles? number[] [0.5, 0.9, 0.95, 0.99]
Request durations histogram
Property Type Default value
name? string 'http_request_duration_seconds'
help? string 'request duration in seconds'
buckets? number[] [0.05, 0.1, 0.5, 1, 3, 5, 10]

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HTTP routes metrics in Prometheus

The following table shows what metrics will be available in Prometheus (subject to the enabled configuration option). Note suffixes like _bucket, _sum, _count are added automatically.

metric labels description
http_request_duration_seconds_count method, route, status_code Requests total count
http_request_duration_seconds_bucket method, route, status_code Requests durations by bucket
http_request_summary_seconds method, route, status_code Requests duration percentiles
http_request_summary_seconds_count method, route, status_code Requests total count

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API Docs

See docs.

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See changelog.

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See also

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Licensed under MIT.

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