- Apple bars web apps from the only App Store allowed on iOS.
- Apple forces developers of competing browsers to use their engine for all browsers on iOS, restricting their ability to deliver a better version of the web platform.
- Apple claims that browsers on iOS are platforms sufficient to support developers who object to the App Store’s terms
…and a proposition:
Apple’s iOS browser (Safari) and engine (WebKit) are uniquely under-powered. Consistent delays in the delivery of important features ensure the web can never be a credible alternative to its proprietary tools and App Store.
This is a bold assertion, and proving it requires overwhelming evidence. This post mines publicly available data on the pace of compatibility fixes and feature additions to assess the claim.
Steve & Tim’s Close-up Magic #
Misdirections often derail the debate around browsers, the role of the web, and App Store policies on iOS. Classics of the genre include:
Apple’s just focused on performance!
…that feature is in Tech Preview
Apple’s trying, they just added <long-awaited feature>
These points can be simultaneously valid and immaterial to the web’s fitness as a competent alternative to native app development on iOS.
To understand gaps in capabilities Apple has created and maintains between the web and native, we should look at trends rather than individual releases. To know if we’re in a drought, we have to look at reservoir water levels and seasonal rainfall. It might be raining features right this instant, but weather isn’t climate.
Before we get to measuring water levels, I want to make some things excruciatingly clear.
First, what follows is not a critique of individuals on the Safari team or the WebKit project; it is a plea for Apple to fund their work adequately. They are, pound for pound, some of the best engine developers globally and genuinely want good things for the web. Apple Corporate is at fault, not Open Source engineers or the line managers who support them.
Second, browser projects having different priorities at the leading edge is natural and healthy. So is speedy resolution and agreement. What’s unhealthy is an engine trailing far behind for many years. Even worse are situations that cannot be addressed through browser choice. It’s good for teams to be leading in different areas, assuming that the “compatible core” of features continues to expand at a steady pace. We should not expect uniformity in the short run — it would leave no room for leadership.
Lastly, while this post does measure the distance Safari lags, let nobody mistake that for the core concern: iOS App Store policies that prevent meaningful browser competition are at issue here.
Safari trails competing MacOS browsers by roughly the same amount, but it’s not a crisis for the web because genuine browser choice provides users and developers meaningful alternatives. MacOS Safari is compelling enough to have held a 40-50% share for many years running, and do so amidst stiff competition. Safari has many good features, and in an open marketplace, choosing it (or not) is entirely reasonable. That is not the topic of this post.
The Performance Argument #
As an engineer on a browser team, I’m privy to the blow-by-blow of various performance projects, benchmark fire drills, and the ways performance marketing (deeply) impacts engineering priorities.
All modern browsers are fast, Chromium and Safari/WebKit included. No browser is always fastest in every area today. As reliably as the Sun rises in the East, benchmarks lost launch projects to re-architect internals, intending to pull ahead. This is as it should be.
Healthy competitions feature competitors trading the lead with regularity. Spurious reports of “10x worse” performance merit intense scepticism.
After 20 years of neck-in-neck competition, often starting from common code lineages, there just isn’t that much left to wring out of the system. Consistent improvement is the name of the game, and it can still have positive impacts, particularly as users lean on the system more heavily over time.
All browsers are deep into the optimisation journey, forcing complex tradeoffs. Improving things for one type of device or application can regress them for others. Significant gains today tend to come from (subtly) breaking contracts with developers in the hopes users won’t notice. There isn’t a massive gap in focus on performance engineering between engines.
Small gaps and a frequent hand-off of the lead imply differences in capability and correctness aren’t the result of one team focusing on performance while others chase different goals.
Finally, the choice to fund feature and correctness work is not mutually exclusive to improving performance. Many delayed features on the list below would allow web apps to run faster on iOS. Internal re-architectures to improve correctness often yield performance benefits too.
The Compatibility Tax #
Web developers are a hearty bunch; we don’t give up at the first whiff of bugs or incompatibility between engines. Deep wells of knowledge and practice centre on the question: “how can we deliver a good experience to everyone despite differences in what their browsers support?”
Adaptation is a way of life for skilled front enders.
The cultural value of adaptation has enormous implications. First, web developers don’t view a single browser as their development target. Education, tools, and training all support the premise that supporting more browsers is better (ceteris paribus), creating a substantial incentive to grease squeaky wheels. Therefore, bridging the gap between leading and trailing-edge browsers is an intense focus of the web development community. Huge amounts of time and effort are spent developing workarounds (preferably with low runtime cost) for lagging engines. Where workarounds fail, cutting features and UI fidelity is understood to be the right thing to do.
Put another way; it’s possible to deny web developers access to features simply by failing to deliver them at the margin. For web developers, compatibility across engines is key to productivity. To the extent that an engine has more than 10% share (or thereabouts), developers tend to view features it lacks as “not ready”.
To judge the impact of iOS along this dimension, we can try to answer a few questions:
- How far behind both competing engines is Safari regarding correctness?
- When Safari has implemented essential features, how often is it far ahead? Behind?
The yellow Safari line is a rough measure of how often other browsers are compatible, but Safari’s implementation is wrong. Conversely, the much lower Chrome and Firefox lines indicate Blink and Gecko are considerably more likely to agree and be correct regarding core web standards.
wpt.fyi‘s new Compat 2021 dashboard narrows this full range of tests to a subset chosen to represent the most painful compatibility bugs:
In almost every area, Apple’s low-quality implementation of features WebKit already supports requires workarounds. Developers would not need to find and fix these issues in Firefox (Gecko) or Chrome/Edge/Brave/Samsung Internet (Blink). This adds to the expense of developing for iOS.
Converging Views #
The Web Confluence Metrics project provides another window into this question.
Engines add features at different rates, and the Confluence graphs illuminate both the absolute scale of differences and the pace at which releases add new features. The data is challenging to compare across those graphs, so I extracted it to produce a single chart:
Higher is better.
In line with Web Platform Tests data, Chromium and Firefox implement more features and deliver them to market more steadily. From this data, we see that iOS is the least complete and competitive implementation of the web platform, and the gap is growing. At the time of the last Confluence run, the gap had stretched to nearly 1000 APIs, doubling since 2016.
Perhaps counting APIs gives a distorted view?
Some minor additions (e.g. CSS’s new Typed Object Model) may feature large expansions in API surface. Likewise, some transformative APIs (e.g. webcam access via
getUserMedia() or Media Sessions) may only add a few methods and properties.
To understand if intuitions formed by the Web Confluence data are directionally correct, we need to look more deeply at the history of feature development and connect APIs to the types of applications they enable.
Material Impacts #
Browser release notes and caniuse tables since Blink forked from WebKit in 2013 capture the arrival of features in each engine over an even longer period than either WPT or the Confluence dataset. This record can inform a richer understanding of how critical individual features and sets of capabilities unlock new types of apps on the web.
Browsers sometimes launch new features simultaneously (e.g., CSS Grid and ES6). More often, there is a lag between the first and the rest. To provide a sizeable “grace period”, and account for short-run differences in engine priorities, we look primarily at features with a gap of three years or more.
What follows is an attempt at a full accounting of features launched in this era. A summary of each API and the impact of its absence accompanies every item.
Where Chrome Has Lagged #
It’s healthy for engines to have different priorities, leading every browser to avoid certain features. Chrome has missed several APIs for 3+ years:
- Storage Access API
Introduced in Safari three years ago, this anti-tracking API was under-specified, leading to significant divergence in API behaviour across implementations. The low quality of Apple’s initial versions of “Intelligent Tracking Prevention” created a worse tracking vector(pdf) (subsequently repaired).
- CSS Snap Points
Image carousels and other touch-based UIs are smoother and easier to build using this feature. Differences within the Blink team about the correct order to deliver this vs. Animation Worklets led to regrettable delays.
- Initial Letter
An advanced typography feature, planned in Blink once the LayoutNG project finishes.
Makes “fixed” elements in scroll-based UIs easier to build. The initial implementation was removed from Blink post-fork and re-implemented on new infrastructure several years later.
Wide gamut colour is important in creative applications. Chrome does not yet support this for CSS, but is under development for
- JPEG 2000
Where iOS Has Lagged #
Some features in this list were launched in Safari but were not enabled for other browsers forced to use WebKit on iOS (e.g. Service Workers,
getUserMedia). In these cases, only the delay to shipping in Safari is considered.
Provides access to webcams. Necessary for building competitive video experiences, including messaging and videoconferencing.
These categories of apps were delayed on the web for iOS by five years.
Real-time network protocols for enabling videoconferencing, desktop sharing, and game streaming applications.
Delayed five years.
- Gamepad API
Fundamental for enabling the game streaming PWAs (Stadia, GeForce NOW, Luna, xCloud) now arriving on iOS.
Delayed five years.
- Audio Worklets
Audio Worklets are a fundamental enabler for rich media and games on the web. Combined with WebGL2/WebGPU and WASM threading (see below), Audio Worklets unlock more of a device’s available computing power, resulting in consistently good sound without fear of glitching.
After years of standards discussion and the first delivered to other platforms in 2018, iOS 14.5 finally shipped Audio Worklets this week.
A veritable poster-child for the lateness and low quality of Safari amongst web developers, IndexedDB is a modern replacement for the legacy WebSQL API. It provides developers with a way to store complex data locally.
Had Apple shipped a usable version in either of the first two attempts, IndexedDB would not have made the three-year cut. The release of iOS 10 delivered a workable version, bringing the lag with Chrome and Firefox to four and five years, respectively.
- Pointer Lock
Critical for gaming with a mouse. Still not available for iOS or iPadOS.
- Media Recorder
Fundamentally enabling for video creation apps. Without it, video recordings must fit in memory, leading to crashes.
This was Chrome’s most anticipated developer feature ever (measured by stars). It was delayed by iOS for five years.
- Pointer Events
A uniform API for handling user input like mouse movements and screen taps. First proposed by Microsoft, it dramatically simplifies input handling. Critical in adapting web content to mobile, particularly regarding multi-touch gestures.
Delayed three years.
- Service Workers
Key API enabling modern, reliable offline web experiences and PWAs.
- WebM and VP8/VP9
Royalty-free codecs and containers; free alternatives to H.264/H.265 with competitive compression and features. Lack of support forces developers to spend time and money transcoding and serving to multiple formats (in addition to multiple bitrates).
They are supported only for use in WebRTC but not the usual mechanisms for media playback (
- CSS Typed Object Model
Not available for iOS.
- CSS Containment
Not available for iOS.
- CSS Motion Paths
- Media Source API (a.k.a. “MSE”)
Only available on iPadOS.
Browser support for the full Web Animations API has been rocky, with Chromium, Firefox, and Safari all completing support for the full spec the past year.
element.animate(), a subset of the full API, has enabled developers to more easily create high-performance visual effects with a lower risk of visual stuttering in Chrome and Firefox since 2014.
Seemingly trivial but deceptively foundational. Lets developers integrate with the browser’s internal mechanism for message passing.
Delayed by nearly three years on iOS.
- Web Performance APIs
iOS consistently fails to provide modern APIs for measuring web performance by three or more years. Delayed or missing features are not limited to:
The impact of missing Web Performance APIs is largely a question of scale: the larger the site or service one attempts to provide on the web, the more critical reliable measurement becomes.
Modern, asynchronous network APIs that dramatically improve performance in some situations.
Delayed two to four years, depending on how one counts.
Not every feature blocked or delayed on iOS is transformative, and this list omits cases that were on the bubble (e.g., the 2.5 year lag for BigInt). Taken together, the delays Apple generates, even for low-controversy APIs, makes it challenging for businesses to treat the web as a serious development platform.
The Price #
Suppose Apple had implemented WebRTC and the Gamepad API in a timely way. Who can say if the game streaming revolution now taking place might have happened sooner? It’s possible that Amazon Luna, NVIDIA GeForce NOW, Google Stadia, and Microsoft xCloud could have been built years earlier.
It’s also possible that APIs delivered on every other platform, but not yet available on any iOS browser (because Apple), may hold the key to unlocking whole categories of experiences on the web.
While dozens of features are either currently, or predicted to be, delayed multiple years by Apple, a few high-impact capabilities deserve particular mention:
The first of two modern 3D graphics APIs currently held up by Apple, WebGL2 dramatically improves the visual fidelity of 3D applications on the web, including games. The underlying graphics capabilities from OpenGL ES 3.0 have been available in iOS since 2013 with iOS 7.0. WebGL 2 launched for other platforms on Chrome and Firefox in 2017. While WebGL2 is in development in WebKit, the anticipated end-to-end lag for this set of critical features is approaching half a decade.
WebGPU will also unlock richer GPU compute for the web, accelerating machine learning and media applications. WebGPU is likely to ship in Chrome in late 2021. Despite years of delay in standards bodies at the behest of Apple engineers, the timeline for WebGPU on iOS is unclear. Keen observers anticipate a minimum of several years of additional delay.
- WASM Threads and Shared Array Buffers
Web Assembly (“WASM”) is supported by all browsers today, but extensions for “threading” (the ability to use multiple processor cores together) are missing from iOS.
Threading support is critical to enabling richer and smoother 3D experiences, games, AR/VR apps, creative tools, simulations, and scientific computing. The history of this feature is complicated, but TL;DR, they are now available to sites that opt in on every platform save iOS. Worse, there’s no timeline and little hope of them becoming available soon.
Combined with delays for Audio Worklets, modern graphics APIs, and Offscreen Canvas, many compelling reasons to own a device have been impossible to deliver on the web.
Now in development in WebKit after years of radio silence, WebXR APIs provide Augmented Reality and Virtual Reality input and scene information to web applications. Combined with (delayed) advanced graphics APIs and threading support, WebXR enables critical immersive, low-friction commerce and entertainment on the web.
Support for a growing list of these features has been available in leading browsers across other platforms for several years. There is no timeline from Apple for when web developers can deliver equivalent experiences to their iOS users (in any browser).
These omissions mean web developers cannot compete with their native app counterparts on iOS in critical categories like gaming, shopping, and creative tools.
Developers expect some lag between the introduction of native features and corresponding browser APIs. Apple’s policy against browser engine choice adds years of delays beyond the (expected) delay of design iteration, specification authoring, and browser feature development.
These delays prevent developers from reaching wealthy users with great experiences on the web. This gap, created exclusively and uniquely by Apple policy, all but forces businesses off the web and into the App Store where Apple prevents developers from reaching users with web experiences.
Just Out Of Reach #
One might imagine five-year delays for 3D, media, and games might be the worst impact of Apple’s policies preventing browser engine progress. That would be mistaken.
The next tier of missing features is relatively uncontroversial proposals in development in standards groups that Apple participates in or has enough support from web developers to be “no-brainers”. Each enables better quality web apps. None are expected on iOS any time soon:
- Scroll Timeline for CSS & Web Animations
Likely to ship in Chromium later this year, enables smooth animation based on scrolling and swiping, a key interaction pattern on modern mobile devices.
No word from Apple on if or when this will be available to web developers on iOS.
CSS extensions that dramatically improve rendering performance for large pages and complex apps.
- WASM SIMD
- Form-associated Web Components
Reduces data loss in web forms and enables components to be easily reused across projects and sites.
- CSS Custom Paint
- Trusted Types
A standard version of an approach demonstrated in Google’s web applications to dramatically improve security.
- CSS Container Queries
A built-in mechanism for a common UI pattern, improving performance and consistency.
Improves focus management and accessibility.
- Browser assisted lazy-loading
Reduces data use and improves page load performance.
Fewer of these features are foundational (e.g. SIMD). However, even those that can be emulated in other ways still impose costs on developers and iOS users to paper over the gaps in Apple’s implementation of the web platform. This tax can, without great care, slow experiences for users on other platforms as well.
What Could Be #
Beyond these relatively uncontroversial (MIA) features lies an ocean of foreclosed possibility. Were Apple willing to allow the sort of honest browser competition for iOS that MacOS users enjoy, features like these would enable entirely new classes of web applications. Perhaps that’s the problem.
Some crucial features (shipped on every other OS) that Apple is preventing any browser from delivering to iOS today, in no particular order:
- Push Notifications
It’s difficult to overstate the challenges posed by a lack of push notifications on a modern mobile platform. Developers across categories report a lack of push notifications as a deal-killer, including:
- Chat, messaging, and social apps (for obvious reasons)
- e-commerce (abandoned cart reminders, shipping updates, etc.)
- News publishers (breaking news alerts)
- Travel (itinerary updates & at-a-glance info)
- Ride sharing & delivery (status updates)
This omission has put sand in the web’s tank — to the benefit of Apple’s native platform, which has enjoyed push notification support for 12 years.
- PWA Install Prompts
Apple led the way with support for installing certain web apps to a device’s homescreen as early as iOS 1.0. Since 2007, support for these features has barely improved.
Subsequently, Apple added the ability to promote the installation of native apps, but has not provided equivalent “install prompt” tools for web apps.
Apple’s maintenance of this feature gap between native and web (despite clear underlying support for the mechanism) and unwillingness to allow other iOS browsers to improve the situation, combined with policies that prevent the placement of web content in the App Store, puts a heavy thumb on the scale for discovering content built with Apple’s proprietary APIs.
- PWA App Icon Badging
Provides support for “unread counts”, e.g. for email and chat programs. Not available for web apps added to the home screen on iOS.
- Media Session API
Enables web apps to play media while in the background. It also allows developers to plug into (and configure) system controls for back/forward/play/pause/etc. and provide track metadata (title, album, cover art).
Lack of this feature prevents entire classes of media applications (podcasting and music apps like Spotify) from being plausible.
In development now, but if it ships this fall (the earliest window), web media apps will have been delayed more than five years.
- Navigation Preloads
Dramatically improve page loading performance on sites that provide an offline experience using Service Workers.
Multiple top-10 web properties have reported to Apple that lack of this feature prevents them from deploying more resilient versions of their experiences (including building PWAs) for users on iOS.
- Offscreen Canvas
Improves the smoothness of 3D and media applications by moving rendering work to a separate thread. For heavily latency-sensitive use-cases like WebXR, this is a critical component in delivering a good experience.
Helps media apps on the web save battery when doing video processing.
- Compression Streams
Enable developers to compress data efficiently without downloading large amounts of code to the browser.
- Keyboard Lock API
An essential part of remote desktop apps and some game streaming scenarios with keyboards attached (not uncommon for iPadOS users).
- Declarative Shadow DOM
An addition to the Web Components system that powers applications like YouTube and Apple Music. Declarative Shadow DOM can improve loading performance and help developers provide UI for users when scripts are disabled or fail to load.
- Reporting API
Indispensable for improving the quality of sites and avoid breakage due to browser deprecations. Modern versions also let developers know when applications crash, helping them diagnose and repair broken sites.
- Permissions API
Helps developers present better, more contextual options and prompts, reducing user annoyance and “prompt spam”.
- Screen Wakelock
Keeps the screen from going dark or a screen saver taking over at critical moments. Important for apps that present boarding passes and QR codes for scanning, as well as and presentation apps (e.g. PowerPoint or Google Slides).
- Intersection Observer V2
Reduces ad fraud and enables one-tap-sign-up flows, improving commerce conversion rates.
- Content Indexing
An extension to Service Workers that enables browsers to present users with cached content when offline.
A modern, royalty-free video codec with near-universal support outside Safari.
- PWA App Shortcuts
Allows developers to configure “long press” or “right-click” options for web apps installed to the home screen or dock.
- Shared Workers and Broadcast Channels
Coordination APIs allow applications to save memory and processing power (albeit, most often in desktop and tablet form-factors).
Helps developers avoid prompting users for permissions that might be duplicative with apps already on the system. Particularly important for avoiding duplicated push notifications.
- Background Sync
A tool for reliably sending data — for example, chat and email messages — in the face of intermittent network connections.
- Background Fetch API
Allows applications to upload and download bulk media efficiently with progress indicators and controls. Important for reliably syncing playlists of music or videos for offline or synchronising photos/media for sharing.
- Periodic Background Sync
Helps applications ensure they have fresh content to display offline in a battery and bandwidth-sensitive way.
- Web Share Target
Allows installed web apps to receive sharing intents via system UI, enabling chat and social media apps to help users post content more easily.
The list of missing, foundational APIs for media, social, e-commerce, 3d apps, and games is astonishing. Essential apps in the most popular categories in the App Store are impossible to attempt on the web on iOS because of feature gaps Apple has created and perpetuates.
Device APIs: The Final Frontier #
An area where browsers makers disagree fervently, but where Chromium-based browsers have forged ahead (Chrome, Edge, Samsung Internet, Opera, UC, etc.) is access to hardware devices. While not essential to most “traditional” web apps, these features are foundational for vibrant categories like education and creative music applications. iOS Safari supports none of them today, while Chromium browsers on other OSes enable these apps on the web:
- Web Bluetooth
Allows Bluetooth Low Energy devices to safely communicate with web apps, eliminating the need to download heavyweight applications to configure individual IoT devices.
- Web MIDI
Enables creative music applications on the web, including synthesisers, mixing suites, drum machines, and music recording.
- Web USB
- Web Serial
Supports connections to legacy devices. Particularly important in industrial, IoT, health care, and education scenarios.
Web Serial, Web Bluetooth, and Web USB enable educational programming tools to help students learn to program physical devices, including LEGO.
Independent developer Henrik Jorteg has written at length about frustration stemming from an inability to access these features on iOS, and has testified to the way they enable lower cost development. The lack of web APIs on iOS isn’t just a frustration for developers. It drives up the prices of goods and services, shrinking the number of organisations that can deliver them.
- Web HID
Enables safe connection to input devices not traditionally supported as keyboards, mice, or gamepads.
This API provides safe access to specialised features of niche hardware over a standard protocol they already support without proprietary software or unsafe native binary downloads.
- Web NFC
Lets web apps safely read and write NFC tags, e.g. for tap-to-pay applications.
- Shape Detection
Unlocks platform and OS provided capabilities for high-performance recognition of barcodes, faces, text in images and video.
Important in videoconferencing, commerce, and IoT setup scenarios.
- Generic Sensors API
A uniform API for accessing sensors standard in phones, including Gyroscopes, Proximity sensors, Device Orientation, Acceleration sensors, Gravity sensors, and Ambient Light detectors.
Each entry in this inexhaustive list can block entire classes of applications from credibly being possible on the web. The real-world impact is challenging to measure. Weighing up the deadweight losses seems a good angle for economists to investigate. Start-ups not attempted, services not built, and higher prices for businesses forced to develop native apps multiple times could, perhaps, be estimated.
The data agree: Apple’s web engine consistently trails others in both compatibility and features, resulting in a large and persistent gap with Apple’s native platform.
Apple wishes us to accept that:
- It is reasonable to force iOS browsers to use its web engine, leaving iOS on the trailing edge.
- The web is a viable alternative on iOS for developers unhappy with App Store policies.
One or the other might be reasonable. Together? Hmm.
Parties interested in the health of the digital ecosystem should look past Apple’s claims and focus on the differential pace of progress.
Full disclosure: for the past twelve years I have worked on Chromium at Google, spanning both the pre-fork era where potential features for Chrome and Safari were discussed within the WebKit project, as well as the post-fork epoch. Over this time I have led multiple projects to add features to the web, some of which have been opposed by Safari engineers.
Today, I lead Project Fugu, a collaboration within Chromium that is directly responsible for the majority of the device APIs mentioned above. Microsoft, Intel, Google, Samsung, and others are contributing to this work, and it is being done in the open with the hope of standardisation, but my interest in its success is large. My front-row seat allows me to state unequivocally that independent software developers are clamouring for these APIs and are ignored when they request support for them from Apple. It is personally frustrating to be unable to deliver these improvements for developers who wish to reach iOS users — which is all developers. My interests and biases are plain.
Previously, I helped lead the effort to develop Service Workers, Push Notifications, and PWAs over the frequent and pointed objections of Apple’s engineers and managers. Service Worker design was started as a collaboration between Google, Mozilla, Samsung, Facebook, Microsoft, and independent developers looking to make better, more reliable web applications. Apple only joined the group after other web engines had delivered working implementations. The delay in availability of Service Workers (as well as critical follow-on features like Navigation Preload) for iOS users and developers interested in serving them well, likewise, carries an undeniable personal burden of memory.