Then it hit me. What if Alfred be able to do it? I’m a developer, and Alfred is extensible, so I got onto a new project to develop an Alfred extension to do this, just like Google does. Today I think my project is stable enough so I decided to go public with it. You can download the extension here.

How to use it

I’m assuming you’re already an Alfred user with the Powerpack installed. You’ll also be needing Growl to be able to see the results of your queries. After downloading and installing this extension, you can trigger unit conversions with the keyword cv (as in convert). You can change that to something else of your preference, of course.

Performing a unit conversion query with Alfred

Using it is simple. You open the Alfred command window, type the extension keyword and the query and press ENTER. You’ll see the results shown in a Growl notification, and you’ll also get the results copied to the clipboard.

As for the queries and how to phrase them, I won’t make an exhaustive explanation here. I rather prefer to list here some examples of valid unit conversion queries that you can perform. This will give you an idea of how to phrase queries and a sample of the variety of units supported out-of-the-box. The following are examples of valid queries. Be sure to type them in Alfred preceded with the keyword for the extension.

• 10 km in miles
• 100 kph in miles per hour
• 50 pounds in kg
• 134.5 seconds in minutes
• 200 milliliters in cubic centimeters
• 2 acre foot per year in liters per day
• 3 newtons in lb ft / square second
• -40 fahrenheit in celcius
• 1 megaparsec in astronomical units
• 6.5e17 decays per minute in megabecquerels
• 10 gallons in liters

Note how you can refer to units by their long or short name, and also how unit prefixes (like kilo-, milli-, etc.) are supported too. Long unit names can be given in plural or singular form.

You can also convert sums of quantities…

• 1.5 weeks + 2 days in hours
• 2 miles, 3 furlongs and 25 yards in km
• 100 km/h, 10 m/s and 2 feet per minute in miles per hour
• 3 hours 15 minutes in seconds

…or omit certain parts of the query. The following are valid queries too. Try them to see the results.

• 3 leagues
• ounces in grams
• parsec
• 3 minutes 23 seconds

The math is performed internally without loss of precision, so you get very accurate results. Also, you can work with really large or small numbers. Try the following queries:

• 1 cubic parsec in cubic picometers
• 1e-50 meV in petajoules

Supported units and measurements

From the examples above you can get an idea of the range of units and physical properties it supports. I won’t list all the units here, but just to give an idea, this extension supports units over a wide variety of physical properties, most of which are listed below.

Most common properties

Length (distance), time, temperature, mass (weight), area, volume, density, speed, acceleration, angular velocity, momentum, force, pressure, work (energy), power, plane angle, solid angle, amount of substance.

Electricity and magnetism

Electric current, electric charge, voltage, resistance/conductance, capacitance, magnetic flux, inductance.

Light and radiation

Luminous intensity, luminous flux, illuminance, luminous energy (quantity of light), radiation dose, ionizing radiation, radioactivity.

Other properties

Catalytic activity, reciprocal length, acoustic impedance and resistance, thermal resistance, dynamic viscosity, molar concentration, mass flow, volumetric flow.

In addition to physical phenomena, this extension also supports conversion of currency and units of digital information, such as data size and data rate (e.g. bits, bytes, kilobytes, kbits per second). In this last case, in addition to the SI prefixes, it also supports binary prefixes like kibi-, mebi-, etc.

A note about currency exchange rates

In the case of currency conversion, the extension will attempt to update currency exchange rates from the Internet at most once every hour, but it keeps a local cached version. The extension can only update the cached version when it’s used, even if it is not used for currency conversion. But if you spend many hours or days without triggering the extension while being online, you’ll end up with outdated currency conversions.

Also note that currency exchange rates given by this application are for information purposes only. It will always be approximate to what you’ll actually get when exchanging money. For your information, currency exchange rates are obtained by the extension from a wonderful public API hosted at openexchangerates.org, which is based on the currency bot project.

What’s next

First of all, enjoy it. You can also contact me to send feedback, bug reports and suggestions of improvements and new features.

If you’re a developer, you can also contribute to the unit conversion engine that powers this extension. It’s an open source Java library that I authored and published on github. You can check it out here.

Download the Alfred Unit Conversion Extension

Performing unit conversion queries using Google's search box.

Imagine if you could that offline, or even be able to have this functionality available to incorporate it in scripts or other programs as well. Imagine you could have this functionality as an extension in Mac’s AlfredApp.

Introducing Metric: A Unit Conversion Library for Java

I needed this functionality to develop an extension for Alfred, the most wonderful Mac launcher, and I wanted it to work offline, without having to retrieve the results from Google or another online source. So I created a Java library that’s capable of performing unit conversion queries expressed in natural English. I called it simply Metric, made it open source, and published it on Github. You can clone it, fork it, play with it or contribute back if you will. The code is fairly well documented and organized. The library includes some supporting sub-libraries that may be used independently in other projects, including a plural/singular inflector for the English language.

Metric meets Alfred

The original goal of developing a library like Metric was to use it as an Alfred extension. Alfred (http://www.alfredapp.com/) is a wonderful productivity application for Mac, much like Quicksilver or Google’s Quick Search Box, but  a little bit better in my opinion. You can grab a copy of Metric as an Alfred extension here. After you install this extension, you can type unit conversion queries on Alfred using cv as keyword.

Performing a unit conversion query with Alfred

This Alfred extension shows the results of the conversion using Growl, but I guess if you already have a Mac chances are that you Growl installed. If not, you can get it here.

Links and resources

• Metric source code repository on Github
• Unit Conversion extension for AlfredApp
• Alfred App and Growl

Readability Redux

This one takes an article or blog post page and presents it in a reading-friendly format, leaving out all the clutter (sidebars, navigation menus, etc.) and also with a customized font and text styling that makes it more suitable for reading and printing.

A blog post shown in readability mode

I was envy when Safari 5 went out with this as a core feature, so much that I actually considered switching now that Safari has got extensions too. I detest to read articles and blog posts with all the clutter of the page. Particularly when you intend to print the article for further reading, not always web sites provide a good printed alternative, if they provide one at all.

Get Readability Redux

Proxy Switchy!

This one I couldn’t live without. It’s pretty much the equivalent of FoxyProxy on Firefox, if you ever used that. It allows you to define several proxy configurations for you to switch to, and you can also create rules so that different specific web-sites that you define are automatically routed through certain proxies all the time, without you having to remember switching. For an active Tor user like me, this one is very handy.

Get Proxy Switchy

Twitter share this page

Tweetie for Mac is great. It helps you keep informed of tweets from those you follow, and you can tweet yourself as well. But when you’re on Chrome reading a web page that you feel you ought to share with the world, it’s simpler to use this extension instead. Otherwise you would need to manually copy and paste the URL and then type your message.

With ‘Twitter share this page’ you just press a twitter icon on the right side of the address bar and voilá! Chrome opens Twitter in another tab with your message ready to be sent, or to be customized first if you wish. It automatically uses the web page title as a message along with the URL already shortened if needed.

Get Twitter share this page

XML Tree

Ever tried to load a XML document in Chrome? It simply shows the text without all the node tags and structure of the XML. This extension fixes this odd behavior, showing the XML tree structure. It says it allows you to collapse and expand nodes, but that doesn’t work for me, perhaps because I am using Chrome 6 from the Dev channel.

An XML Document being shown as a structured tree of nodes

For a developer like myself this one is a must. I always wondered why this was not a core feature of the browser itself, like it is in Firefox. Even for uneducated users who know nothing about XML, the structured presentation will almost always be more friendly and comprehensible than the default soup of text.

Get XML Tree

Docs PDF/PowerPoint Viewer

I have a couple of other extensions from Google itself, but this one is the most useful. Every time you click a PDF, Word or PowerPoint document on the web, it’ll show a preview using Google Docs’ interface, from which you’ll be able to download the document if you wish.

An online PDF file being shown in the Google Docs viewer

Before this, my downloads folder was always full of lots of documents that I once opened just to take a short look and discard. Now I can have a glimpse of what I clicked on, before I decide if I want to keep it.

Get Docs PDF/PowerPoint Viewer

Other extensions I use

Besides this featured five extensions above, there are a few more I use occasionally.

Also, take a look at this list of recommended extensions, from Google itself!

But not everything is perfect…

I am yet to find a youtube downloader extension that actually works. I’ve tried a few with no success. Currently I have to resort to Safari 5 which just recently got extensions support and there’s a pretty good one for this purpose. Besides that, there’s nothing left that I need and haven’t found.

Have something to share about this? What extensions do you find useful? Is there some feature you need for which there’s no suitable extension yet?