Fog Creek

Building for multiple devices

We built Trello from the ground up to work on just about any device. It’s not a simplified version with limited features, either. Trello responds to your device’s screen size and capabilities. It’s the same exact site and the same exact code; a consistent experience that looks, feels, and works the same everywhere.

But we also have an iPhone app. It’s pretty great if I may say so. If you are a Trello user with an iPhone, you should download it now. It’s free. Now that there is a great app, why would we still focus on a mobile web app? One reason is that focusing on mobile makes Trello better as a whole.

Everything we do for mobile translates back to a better desktop experience. This wasn’t the first reason we wanted to implement a responsive design, but it turned out to be the most important. Keeping mobile in mind focuses us on creating a fast and easy-to-use interface. Trello gets data super fast, but the page must also render quickly. That stops us from using complex interactions and some of the more whiz-bang CSS features. This translates back to rendering speed on your desktop, which isn’t likely to be an overclocked gaming rig with 32GB of RAM.

All the interface elements are mobile-friendly, which means they are also more desktop-friendly. Buttons and menus have big, friendly hit targets. Interactions are straight-forward. We don’t rely on hidden hover effects and if we’ve got a complex interaction, it will have a fallback for touch devices.

There are no redirects. Let’s say you’re on your phone and somebody links to from Twitter. You’re able to watch the video, read the pitch, sign up, and try it out. You are left with a good impression, no nonsense. No screaming “DOWNLOAD THE APP!” page, no switching out of whatever app your using, and you won’t be redirected five times and land on the homepage. You just get the information and it works.

Scaling, zooming, and resizing work seamlessly. Sometimes you want to use a small browser window on a desktop. Maybe you’ve got a side monitor with a Trello board and your mail app open while your text editor or photo editor are up on your main screen. The horizontal board view won’t work at smaller window sizes, but Trello will adapt to a view that does. If you need bigger or smaller text, you can zoom in (or out) as much as you need and Trello will use a view that works. Got a huge monitor and want to project your Trello board for all to see? Trello will work for that as well. Is it way far back in the office? Just zoom in and text will be readable.

We can deliver updates to all devices seamlessly. We have a single codebase and one place to deploy, which means updates are easy. We don’t have to retro-fit new features to a separate codebase, worry about new workflows or interactions, or think about how some URL is going to work. This lets us develop and ship features faster.

So how does it all work?

Here are some of the tools and tricks that made developing a responsive interface much easier.

Use a limited library of mobile-optimized, reusable components. Each component can be collapsed into a single column or otherwise adjusts for smaller screen sizes. The same layout elements used for the back of cards are used in the organization profile and a bunch of other pages. Our context menus (those small pop-ups used to do things like assign members and select labels) are narrow enough that they will fit on any screen. We have some one-offs like the landing page and the board, but they are few and far between. For the most part, we don’t have to ask how a new feature is going to work on mobile because any component we use will already be mobile-optimized.

Card menu on card detailThink twice about navigation. The card sidebar typically has navigation and buttons for voting, assigning, and the like. It collapses below the main column with a smaller window, which means you would have to scroll and scroll to get to that vote button you were looking for. We added a card menu to the header on the back of cards that lets you easily vote, add due dates, assign members, and everything else without wearing out your thumb.

Use a vector-based image editor like Illustrator to produce icons. We wanted to make sure icons looked sharp on devices with a higher pixel ratio like the the iPhone 4. We use a CSS sprite sheet that has every icon used on the site. We can easily export a higher resolution version using Illustrator, and serve it to capable devices using some simple CSS media queries. UPDATE: now uses an icon font for icons! Icon fonts are faster, Retina-ready, and easier to work with. You can read about our experience converting to an icon font here.

Trello icon sprite sheet

That being said…

We’re developing for the browsers and devices of today and tomorrow. We don’t have spare development time, so we can’t spend any on browsers and devices that won’t be around in two to three years. Trello won’t work on the RAZR, for instance. It also doesn’t work on every ‘smart’ device. Internet Explorer 8 doesn’t have the technical capabilities to run Trello. The Windows Phone 7.0 browser is based off of IE8, so it won’t work either. But it will work on Android 2.3+, iOS 4.0+, Windows Phone 7.5 (Mango), and others. Are we neglecting would-be happy users? Perhaps. But we can provide more value to more people by shipping features faster and that’s better in the long run.

And we still love native apps! Apps provide things we can’t get out of the web: better speed, offline support, smooth animations, push notifications, and a native look and feel. Native apps will provide a better experience to a broader reach. We just don’t think the mobile web should be ignored because of them.

Designing for multiple devices has deeply influenced our design decisions and made for a better, faster, and easier-to-use product. There are plenty of improvements to be made, but we’re happy with the foundation we’ve set. Sign up now and check it out for yourself.