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2.0.5 • Public • Published


Viz is a small plugin for crow-metrics that exposes your server's metrics over HTTP using express. It collects snapshots over a rolling window (one hour, by default) and graphs this data on a web page.


There are two ways to construct the service:

  • viz(metrics: Metrics, options: VizOptions = {}): express.Router

    Create an express router that will respond to a path with the viz interface. This is useful if your server is already using express for other requests.

    • express - the express module or a compatible one
    • metrics - a crow Metrics object
    • options - passed to the RingBuffer:
      • span: number - how many milliseconds to buffer (default is one hour, or 3600 * 1000)
      • prometheus: boolean - if true, a prometheus document will be hosted at /metrics

    For example:

    const express = require("express");
    const { Metrics } = require("crow-metrics");
    const { viz } = require("crow-metrics-viz");
    const app = express();
    const metrics = Metrics.create();
    app.use("/admin/viz", viz(express, metrics));

    This will add the viz paths under /admin/viz on your express server.

  • startVizServer(metrics: Metrics, port: number = 8080, options: VizOptions = {})

    Start up the viz site on a devoted port with a new instance of express.

    For example:

    const { Metrics } = require("crow-metrics");
    const { startVizServer } = require("crow-metrics-viz");
    const metrics = Metrics.create();
    startVizServer(metrics, 9090);

    This will create a page at http://localhost:9090/.


  • /

    A small webpage that loads the content from /history.json and draws an SVG graph for each one. This is meant to give a quick human-readable overview of the server instance's metrics.

  • /current.json

    A JSON object where each key is the name of a metric, and each value is its current value.

  • /history.json

    A JSON object where each key is the name of a metric, and each value is an array of the metric's values over the past hour (or whatever span you configured), in order from oldest to newest. A special key "@timestamp" gives an array of the corresponding timestamps for these values, in epoch seconds.

  • /metrics

    A prometheus-formatted plaintext metrics snapshot, if requested in options.


Apache 2 (open-source) license, included in LICENSE.txt.


@robey - Robey Pointer



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