Prevents you from being on reddit or facebook all day
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Andrew Moffat
Latest commit 012acad Sep 11, 2012 helps you keep focused by applying schedulable firewall rules to distracting websites. An example firewall rule looks like this:

def domain_reddit_com(dt):
    return dt.hour == 21 # allow from 9-10pm



Add the following line to the top of your /etc/resolv.conf, before any other nameservers:


Mac OS X

Go to System Preferences -> Network -> Advanced -> DNS and add as your DNS server.

Now start Focus:

sudo python &

Filtering Domains

Firewall rules involving schedules and timeframes can get complicated fast. For this reason, the scheduling specification is pure Python, so you can make your filtering rules as simple or as complex as you want.

The default filter rules is created on first startup in /etc/

import re

def domain_ycombinator_com(dt):
    # return dt.hour % 2 # every other hour
    return False

def domain_reddit_com(dt):
    # return dt.hour in (12, 21) # at noon-1pm, or from 9-10pm
    return False
def domain_facebook_com(dt):
    return False

def default(domain, dt):
    # do something with regular expressions here?
    return True

The format is simple; Just define a function named like the domain you want to block, preceeded by "domain_". Have it take a single datetime object and have it return True or False. In the body, you can write whatever logic makes the most sense for you. Maybe you want to write your own Pomodoro routine, or maybe you want to scrape your google calendar for exam dates, and block certain websites on those dates.

For sites without their own scheduler function, the default() function is called.

There's no need to restart Focus if you redefine your schedules.

Configuration tries to start with a sensible configuration, but if you need to change it, edit /etc/focus.json.conf

How it works is, at its core, a DNS server. By making it your primary nameserver, it receives all DNS lookup requests. Based on the domain name being requested, it either responds with a "fail ip" address (blocked), or passes the request on to your other nameservers (not blocked). In both cases, Focus adjusts the TTL of each DNS response so that the service requesting the DNS lookup will do minimal caching on the IP, allowing Focus's filtering rules to be more immediate.


  • Q: I started Focus, but it's not blacklisting the site I picked.

  • A: Your browser may be caching that site's ip. Give it a few minutes.

  • Q: Why do I need to start Focus with sudo?

  • A: Focus needs to listen on a privileged port as a DNS server.

  • Q: How do I stop Focus?

  • A: Focus writes its process id to /var/run/ Kill the process using this process id.