It seems like ever since Frances Berriman  coined the term “Progressive Web App” in an effort to describe a new class of website, there’s been a great deal of confusion over exactly what a Progressive Web App (PWA) is. Sure, her husband, Alex Russell, put together a handy guide to the characteristics of a PWA, and they have been the subject of reams of documentation, dozens of blog posts, and equally as many conference talks.

Even with so much well-written, accessible content about PWAs freely available, misinformation abounds. Maybe you’ve run into one or more of these:


  • If you’re building a PWA, you need to use a JavaScript framework.

  • To build a PWA, start with a single page app.

  • PWAs only make sense for “apps” your users want to install.

  • PWAs only make sense in mobile.

  • PWAs are an Android thing.

None of these are true, but like so much misinformation these days, each contains a shred of truth that has been contorted into a falsehood. If you’re considering building a PWA, you might use a JavaScript framework or build it as a single page app, but it’s by no means necessary. They’re an option for building a PWA just like they’re an option for any other web project. After all, every PWA is (or at least should be) a website. PWAs just have some features that empower them to do more than websites have traditionally been able to… like install. But, similarly, installation is not the raison d’être of every PWA. And, while many of the first PWAs were focused on mobile and only worked on Android, PWAs are not limited to small screen devices anymore. They’re also more than a Google thing too; Microsoft, Mozilla, Opera, and Samsung are all on board. Apple recently declared their intent to implement Service Workers (one of the technical underpinnings of PWAs), but time will tell if they’ll support aspects like installation. No matter, as Progressive Web Apps work really well in Safari anyway!

Sadly, misinformation like this has convinced many designers and developers (and their management teams) that PWAs aren’t appropriate for their projects. They are! Your site—every site—should be a PWA. This approach offers benefits for every project on the web, but I’ll get to that in a minute. Before I do, I want to level-set on what, exactly, makes a PWA a PWA. If you’ve been tracking PWAs closely or have already built one, you can skim or skip the next section. If you aren’t all that familiar or don’t feel like you have a good grasp on what they are, no worries, the next section is a very brief primer that will get you up to speed quickly.

So what is a PWA?

As I mentioned, a PWA is a website with special powers. The term “app” in the “Progressive Web App” is not indicative of the sort of content or experience users should expect with a PWA. You shouldn’t get hung up on it; “Progressive Web App” is a marketing term. PWAs have the ability to connect with the operating system (and, thereby, its users) on a deeper level through installation and APIs offering capabilities like notifications, access to the address book, and more. Not all of these APIs require installation for access, but some do. It may help to think about a PWA as being a website++.

What makes a PWA a PWA? Not much, actually; there are only three requirements:


  1. You need to be running under HTTPS. PWAs can be granted a whole host of extra privileges in an operating system, so it’s critical that the connection to your web server be secure. If you need help with this, you should check out the free SSL service Let’s Encrypt.

  2. You need a Web App Manifest. This is a lot less scary than it sounds. It’s a JSON file with information about your site. You may even have a bare-bones one already if you’ve used a favicon generator. Make sure you reference it using a link in the head of your web pages so browsers and search spiders can find it.

  3. You need a Service Worker. This is probably the most complicated step, but there are a ton of recipe guides out there for creating Service Workers tailored to the kind of jobs you want them to do. This one, from Mozilla, is especially good.

That’s it. Once you have those in place, your website is a Progressive Web App. At least technically. Why the qualification? Well, this is where things get a little more nuanced.

Back in 2015, when he debuted the PWA concept, Alex Russell outlined ten characteristics PWAs shared (or at least were capable of). Most of those characteristics are, without a doubt, how we should be building for the web. Others are not as universal and would not make sense in every kind of project. I suspect that might be one of the sources of confusion for folks considering adopting the PWA approach and it’s the reason I decided to write this article.

Quality experiences and the universal benefits of PWAs

In the next few sections, I will discuss several web project archetypes and how adopting some of these PWA characteristics can benefit their users. After all, that’s who we’re doing this for. But before I get to that, I want to discuss the seven characteristics of PWAs that are useful in any web project.

As I mentioned, there are some characteristics of PWAs that will absolutely provide value to your users and are well worth your time and consideration. In fact, all of them are considered best practices in web design and development.

First off, PWAs must be safe. As I mentioned in my discussion of their technical requirements, PWAs must be running under HTTPS. Period. Thankfully, the cost of running your site under HTTPS has dropped to zero. Sure, there are legitimate challenges to converting large existing websites over, but it’s worth it for so many reasons. The primary one is that it protects your users from malicious man-in-the-middle attacks being made by ISPs, in hotels and airports, infected routers, or others with network access. HTTPS ensures that both the code and content you send to your users actually arrives intact. It’s not fool-proof, but it’s an important step in protecting your users and your data. Running HTTPS is also a prerequisite for access to many of the newer (and more sensitive) APIs including Geolocation and Service Workers and for performance-boosting technologies like HTTP/2 and Brotli compression. It’s also worth noting that many browsers are beginning to mark non-HTTPS sites “unsafe” and SSL also affects search ranking.

I mentioned earlier that PWAs were never intended to be a mobile-only approach. PWAs are for everyone. Making your project available to more people on more devices with wildly varying operating systems, browser capabilities, system APIs, and screen sizes is only going to increase your reach and create more opportunities to be successful. This is where progressive enhancement and responsive design come in. By building responsive layouts, your designs will adapt to provide the most appropriate layout given the screen real estate you have to work with, whether dependent on the dimensions of the device or on the window size set by your user. Progressive enhancement enables your projects to adapt to an even wider array of variance, in both the execution environment (device, OS, etc.) and, more importantly, your users.

Progressive enhancement also helps you avoid situations where users can’t access your project because they happen to use a device or browser you’re unfamiliar with or haven’t tested on. It ensures your site works on any device that can access the web, regardless of its capabilities, allowing you to use your valuable time optimizing that experience for more modern browsers and devices. It’s also a more economical approach in the long-run.

Another quality Alex identified was that many PWAs are “app-like”. Note the like. They are not apps, but rather, provide app-like experiences that users that—dare I say it?—enjoy using. The more you can do to provide a consistent, seamless, effortless user experience (which is really what “app-like” is implying here), the more likely you are to see repeat visits, increased sales, etc.. It’s worth noting that this doesn’t mean you have to use JavaScript; it simply means you should think about the flow your users take through your site and take every opportunity to remove the friction from the process of them accomplishing their goals.

If you’ve built something, you probably want folks to find it. PWAs, by definition, are easy to discover. Your site’s content should be written in such a way that it pops up organically when people search for related topics. Don’t get all spammy, but take care to author content in a thoughtful, appropriate, and straightforward way.

Related to discoverability is that PWAs are linkable. If your users can reach a certain point in your site via natural navigation, you should do your best to ensure they can save their place by bookmarking it or when they re-launch their web browser and your site’s tab is re-launched. This also plays into how shareable your project is. You may also want to do yourself a favor and spend some time putting together some Open Graph meta tags and some JSON-LD to make your content even more shareable.

Last, but certainly not least, there’s network independence. This is the big one that gets developers so excited. Offline capabilities and persistent storage has, to some extent, been possible for a while now; heck, Microsoft debuted client-side data storage back in 1999! Alas, while client side data stores—IndexedDB, localStorage, etc.—have definitely come of age in the last few years, true control over resource caching has been pretty abysmal. Then came Service Workers and the Cache API. These two technologies work in concert with the Fetch API to make, intercept, augment, and store resource requests made from within your site, meaning your users may still access your content, even if their network connection is interrupted.

There are a ton of fantastic resources covering the ins and outs of Service Workers, so I’m going to skip the technical stuff and just talk about some of the neat things you can do with them:


  • Prefetch and cache resources you know your users are going to need. This can improve performance dramatically.

  • Cache every page and asset requested by your site so they don’t need to be retrieved from the server each time a new page is loaded. This improves performance on navigation as well as on return visits.

  • Define a custom “offline” page. This prevents users from seeing the browser’s generic “You’re not connected” message.

  • Look for a network connection first and provide the “live” copy of a given resource if it’s available, falling back to a previously cached “stale” version if it’s not. This can also prevent users from seeing “You’re not connected” messages.

  • Respond to requests for JPEG images with WebP (which tend to be considerably smaller) versions of those images if the browser supports them. This strategy allows you to provide alternate image sources that improve performance without having to modify your markup.

Service Workers are capable of a whole lot more—some of which I will get into shortly—and are on track to be granted many more incredibly useful features in the not too distant future. They have already proven their worth and bring value to any project on the web. For a useful list of recipes, check out this cookbook from Mozilla or this one from the Chrome team.

Other PWA benefits by project type

Now that we’ve looked at the universally-beneficial qualities of PWAs, let’s shift gears. Every project is different, but there are a handful of archetypes that most web projects tend to fall into. And each of those archetypes can derive real benefits from running as a PWA.

Informational

When I think about informational sites, I’m talking about the kinds of sites many of us in the industry refer to as “brochureware.” Vanity sites are a good example of this. Small business sites whose interactivity tops out at a contact for or a phone number link are another. Portfolios would also fall into this category as would many restaurant sites.

In most cases, projects like these are there to serve folks wanting to know more about you, your business, a project, or something similar. In most cases, you’re not going to see a ton of repeat visits. Folks come to the site looking to find out a specific piece of information—which hopefully they can access quickly and easily—and they’re off again. They might return, but they might not, meaning the performance gains provided by a Service Worker’s offline caching could be useful, but likely won’t have quite the level of impact it would have on a site that gets frequent repeat visits. It’s also highly unlikely—though not impossible—that someone will actually install a project like this.

Depending on the type of site you’re building, you might consider integrating some device APIs. If the site is for a brick-and-mortar business, add Geolocation support. If you have sales or specials you’d like to inform your visitors about, you might consider integrating Notifications (either Web or Push).

Even though two of the oft-touted “major” benefits of being a PWA—install-ability and offline capability—are less applicable for informational sites, making projects like these a PWA is still beneficial. Those are just two aspects of being a PWA. Your users will thank you for building a site that works on every one of their devices, is easy to use, comes up in search, and is easily shared with their friends.

Periodical

Periodical sites encompass everything from a blog or newsletter or podcast to online comics, magazines, newspapers, and video programs. These sorts of projects are like informational projects, but are updated regularly (or semi-regularly). They also have an audience that is likely to return (ahem) periodically to read a new article, watch a new video, or listen to a new podcast episode. Since they share much of their DNA with informational sites—heck, a periodical may even be part of an informational site—all of the qualities that benefit informational sites benefit periodicals as well. There are, however, some capabilities that PWAs offer that periodicals are perfectly suited to take advantage of.

In discussing promotions or specials, I mentioned that Push Notifications could be an option for informational sites. They should be a given for a periodical site. Push Notifications provide a mechanism for your server to send an update to any instances of your Service Worker that are installed on your users’ machines. And, assuming they’ve granted you permission, those updates can be displayed to your users even if they don’t have your PWA installed or a browser tab open to your site.

Don’t take this as an opportunity to spam your users, as you’ll likely lose their eyeballs and business. Instead, choose appropriate times to ping them. If your site only gets updates once or twice a week, notifying them of individual posts is probably good and can provide a nice alternative for folks who don’t use a feed reader. If you have frequent updates, consider a daily or weekly roll-up. This might even be a good candidate for some A-B testing.

You could also up your game by offering an easy in-page tool for saving an article for offline reading. Why would you want to do that rather than caching everything the user ever sees using the Service Worker? Well, given the nature of a periodical, the reuse of individual content items is likely pretty low. If you cache everything the use ever sees—especially if your content contains a lot of high resolution images—you’re gonna be filling their cache up with stuff they may never want to see again. In order to be a good web citizen, you could either clean that up regularly by keeping track of the last time a resource was accessed (which, frankly, seems like a lot of work) or you could cache just the necessary long-lived resources like your CSS and JavaScript files. Then you can put your users in control by providing a button that enables them to save an entry for later.

Continuing our journey through Service Worker land, you could start exploring Background Sync to pull in new resources periodically. If you’re a newspaper, maybe you want to prime your users’ caches every morning with the front page and the top feature stories. If you’re a podcast, maybe you want to load in the newest episode on a regular cadence. Again, to play nicely in the sandbox, you’ll probably want to trash older articles, episodes, and so on, but this could be a great way to provide an incredibly fast experience for your users. Think about it… they launch your site and the browser already has everything it needs to render today’s issue. Magic!

Finally, periodicals are one of those archetypes where the option to install your site begins to make sense. Some people like being able to hit an icon on their home screen or in the Start Menu to access their local newspaper. It’s not for everyone and may not be right for every periodical, but it’s an option. And offering your users the ability to install your PWA comes for free, so you may as well embrace it and make sure your Web App Manifest has been thoughtfully authored to provide a good user experience when your PWA is installed.

Transactional

Any site that facilitates the exchange of information could be considered transactional. The most common examples include online shops, banking and stock trading tools, travel booking systems, and payment portals. PWAs have, to a large extent, already proven their value in this area. A quick peek on PWA Stats revealed the following “wins”:


  • The Raphael Hotels increased website conversions by 20%, pageviews by 66%, sessions by 59%, and reduced bounce rate 51%.

  • MakeMyTrip saw a 3× increase in conversion and 160% increase in shopper sessions and first-time shoppers are 3× more likely to convert on the PWA than in native app.

  • Lancôme saw a 17% increase in conversions, a 51% increase in mobile sessions overall and a 53% increase on iOS alone.

The kicker on that last one? iOS doesn’t even support Service Workers!

It’s well-known that improving page performance increases conversions, so the speed improvements granted by a smart caching and offline strategy with Service Workers are incredibly important here. But there are numerous other ways PWAs can benefit transactional sites as well.

Since I mentioned offline, I’ll add that your offline strategy should not begin and end with Service Workers. For a while now, we’ve used cookies to track transactional data shopping cart contents, but cookies have always been severely limited in terms of the amount of data they can store because they get sent along with every network request. With IndexedDB, localStorage, and sessionStorage, we have the ability to store more (and richer) data about the transaction taking place on the client side. Storing this information on the client makes it easier to recover from problems like a network loss. If a transaction fails, you will still have access to the data (which might have otherwise been lost in a failed POST) and you can either periodically try the transaction again or wait until you see the network is back before submitting it. Either way, adding real-time messaging about what’s going on and how you are working to resolve it will go a long way toward assuring your users that their data is not lost.

If your project is highly transactional, you will definitely want to look at Background Sync as a means of keeping your users’ local data in sync with server data. For example, if you are building a banking system, synchronizing information like recent transactions and current balances will be incredibly useful to your customers. Same goes with current stock prices and balances if you’re working on a trading platform.

In most transactional scenarios, notifications can be quite helpful. Borrowing on the scenario I mentioned earlier, notifications can be used to let someone know when their transaction has completed (after all, in a PWA you could complete the transaction during a Background Sync when your site isn’t running). Notifications come in a two flavors: Web Notifications are triggered via JavaScript in an active page, Push Notifications are sent from the server and can be delivered even when the site isn’t open. Depending on the scenario, one or the other will probably make more sense. Just be aware that Push Notifications are not as well supported as Web Notifications… yet.

For transactional sites that are frequently accessed (and I realize “frequently” is a very relative term) the install-ability of a PWA is a huge win. Isolating your site within its own app container allows users to focus on the task at hand, without the distraction of other tabs. It also insulates the processes running your code from the process running all of the sites they have open in their browser. Additionally, it has less overhead since there’s no browser chrome running alongside it. All of these benefits work together to create a streamlined, frictionless experience for your users.

Once installed, many operating systems will grant your project access to internal APIs. Perhaps you want to let them choose an address to ship a gift to, from their contacts. Or maybe you want to enable them to add the flights they just booked directly to their calendar. Or perhaps you want to voice-enable your app by integrating with their virtual assistant. All of those scenarios become possible in the context of a PWA, which is a huge boon for transactional websites.

Social

Social websites—think Twitter, Facebook, etc.—are excellent candidates for PWA-ification. In fact, Twitter has already gone that route. Social sites combine aspects of periodical and transactional websites, so they naturally inherit many of the benefits of those archetypes. Push Notifications, in particular, are incredibly important for sites like this, as re-engagement is crucial for the long-term success of your platform. Install-ability is also important in that regard.

Performance, especially initialization speed, is going to be an important benchmark for social projects, as users will not sit around waiting for all of their feed items (and their associated imagery, videos, etc.) to load. Caching your site’s assets will help a bit, but—depending on your project goals and situation—you might consider using Background Sync to update your users’ news feeds so they are ready to go (or close to it) the next time they open it up.

As transactional projects, social websites will also benefit from access to device and system APIs when installed. Most social networks, for example, request permission to peruse your Contacts to look for friends and colleagues that are also using the service. If you go that route, it’s imperative that you don’t abuse the privilege by trying to trick your users into spamming their friends with info about your service. If we don’t respect our users and their private information, we run the risk of losing access to it (and them) altogether.

Software

When we talk about “web apps,” often online software is what naturally comes to mind. Some examples include email clients, accounting tools, project management suites, version control systems, and photo editors. In many ways, these are software in the traditional sense, they just exist on the web instead of being installed locally… until now.

Through the magic of PWAs, these software-as-a-service projects can become full-fledged desktop (and mobile) applications. This enables teams that have gone all-in on web technologies to continue (or even increase) their investment in that area without sacrificing the convenience of install-ability on native platforms. Sure, there are absolutely some solid reasons why you might want to customize a native experience for your software, but for the vast majority of cases the web offers everything necessary to run your application… that’s why its on the web in the first place.

Offline data stores, background synchronization, and file system access help to elevate the experience for your users, making this archetype the most obvious beneficiary from Progressive Web Apps.

Institutional

Some projects are, frankly, too sprawling to fall neatly into one archetype or another. I’m thinking of schools, large corporations, mammoth financial institutions. These projects are often an amalgam of many or all of the archetypes I’ve covered here. As such, all of the benefits accrued to those archetypes apply, in context of course.

When looking at a large institutional project, it can be difficult to figure out how to assemble an overarching strategy for turning it into a PWA. The good news is that you don’t necessarily have to. You can carve up your project into many individual PWAs that can exist independently.

Take, for example, an online learning system. You could create a PWA for the learning system itself, but you could also carve off each individual course as its own, installable PWA, with its own cache, notifications, etc. The reason you can do this is that Service Workers and Web App Manifests can be scoped. You can scope them to a specific hostname or you could even scope them to a specific path within your URL structure. While obviously more complicated, if you think of each of those courses as having a course template and you think of a Web App Manifest and Service Worker being part of that template, it becomes easier to wrap your head around.

It’s your turn

Progressive Web Apps may seem overly technical or beyond the needs of your project, but they’re really not. They’re just a shorthand for quality web experiences—experiences that can absolutely make a difference in our users’ lives. If you hadn’t considered building a PWA before, I hope this article has changed your mind. And if you’re already neck-deep in Service Workers, perhaps it’s given you some ideas for new ways to approach the projects you’re working on.