A real-time zero-configuration web-based tail

npm install lucidtail
42 downloads in the last month


A real-time zero-configuration web-based tail. It broadcasts events such as new lines added to any monitored files, new UDP messages, and those emitted by other EventEmitters to your browser.

lucidtail Command

The lucidtail command listens to specified sources and displays them in a pretty little web application.

To quickly be able to view your logs at http://localhost:8080 (default):

npm install lucidtail -g # One time global install
lucidtail *.log


You must already have nodejs installed.

Method: Simple

To install lucidTAIL globally:

npm install lucidtail -g

This allows you to use the lucidtail command. You may need root/Administrator access, if you don't have it you can alternately get lucidTAIL from the git repository.

Method: From GIT

Clone lucidTAIL:

git clone git://

You should now be able to use lucidtail/index.js or node lucidtail/index.js instead of lucidtail.


Please see lucidtail --help


lucidtail will use it's default http port (8080) when running.

Monitor Files

lucidtail *.log

Monitors all files ending with '.log'.

Monitor UDP

lucidtail -u 514

Monitors UDP messages on syslog port 514 (which requires root access on most systems).

Publish on port 80

sudo lucidtail *.log -u 514 -p 80
  • Monitor all files ending with '.log'.
  • Monitor UDP messages on port 514 (syslog).
    • This requires root access on most systems.
  • Publish on port 80
    • This requires root access on most systems.

Advanced Setups


The examples assume you have either added lucidtail to your package.json or executed:

npm install lucidtail



Monitors a test emitter (which sends a test message every second) and publish events on the default port (port 8080):


    .use('udp4', 5000);

Monitors UDP messages on port 5000.


The following will display inbound syslog messages (UDP port 514) on HTTP port 80:


  • This example requires lazy which is on npm.
  • Port 80 and 514 may require root/Administrator privileges to bind.


var lucidtail = require('lucidtail'),
    lazy = require('lazy');

// Use a simple regex to parse out the values in the message
// Not even RFC 3164, but this is just an example.
var regex = /(<\d+>)?(\w{3} +\d+ \d{2}:\d{2}:\d{2})?( \w+)?( \w+\[?\d*\]?)?: (.*)/;
var syslog = lazy(lucidtail.emitter('udp4', 514))
    .map(function(data) {
        var matches =;
        if (matches) {
            if (matches[1])
                data.pri = matches[1].replace(/[<>]/g, '');
            if (matches[2])
       = matches[2];
            if (matches[3])
       = matches[3].substring(1);
            if (matches[4])
                data.application = matches[4].substring(1);
            if (matches[5])
                data.msg = matches[5];
        return data;

// Create aggregate emitter
var emitter = lucidtail(80)
    // Listen to a test emitter


The API is exposed by require('lucidtail') and is still rapidly evolving, but the gist of it is:

lucidtail([server|port=8080][, options])

A convenience method which returns an instance of lucidtail.Aggregator. All events emitted by the returned lucidtail.Aggregator will be sent through a socket to users.

  • 'server|port': either a http.Server or a port (default = 8080)
  • 'options': the options object
    • 'host': http host to listen to (default = INADDR_ANY)
    • 'of': namespace to use


A sub class of events.EventEmitter.

lucidtail.Aggregator.pipe(destination[, events])

Forward events to a destination events.EventEmitter.

  • destination: Destination events.EventEmitter
  • events: An array of events to forward (default: ['data', 'error']) or an object whose key/value pairs are used to map source events (keys) to destination events (value).

lucidtail.Aggregator.listen(source[, events])

The opposite of lucidtail.Aggregator.pipe(destination[, events]).

lucidtail.emitter(name[, arg1, arg2])

A connivence method which creates events.EventEmitters.

  • name object
    • tail: tail a file specified by arg1 (default: 'test')
    • test: Emit a test message every second
    • udp: Emit inbound UDP messages on a port specified by arg1
    • socketio: Pipes emitted events to a socket servicing http.Server arg1.


Creates a http.Server request handler which serves client-side resources.

npm loves you