Version: Smart Feature Phone 3.0

Signed or PWA App

While Signed Apps are the recommended way to deliver your KaiOS apps, there may be benefits to using the PWA approach. This page provides a guide to the key differences between these delivery methods and offers advice on choosing between the two.

The primary difference between Signed Apps and PWA is fairly obvious: the former delivers all its content onto a user’s device, while the latter delivers the app‘s assets on demand from a web server. However, there are many more subtle differences that you should consider when choosing between the two.

Signed and PWA compared

Let’s start by looking at key features of Signed Apps and PWA Apps and see how they differ.


The overriding reason for creating a Signed App is the functionality it can offer to your users. Packaged Apps can use the Signed APIs, which provide apps with the ability to integrate closely with hardware and software features on a KaiOS device. If, for example, your app wanted to allow the user to select and use details of contacts stored on the device, this can only be done in a Packaged App.

FeatureSigned AppsPWA Apps
API supportAll available KaiOS APIsNo access to Signed KaiOS APIs
Device integrationExcellentLimited
Can access web resourcesYesYes


In general you should expect users to observe better response from Packaged Apps, as all the app’s assets are stored locally on their device. When accessing remote data from the Internet, generally there’ll be no significant difference between the two options.

FeatureSigned AppsPWA Apps
Start-up timeFast, all assets on the deviceNetwork limited, all assets downloaded
Network impactRemote data onlyApp content(unless AppCached) and remote data
Content optimization, e.g. screen sizeThrough redundant assets or multiple packagesOn-the-fly
Impact of data plan limitsLowHigh


While KaiOS supports AppCache and local data storage, Signed Apps provide the app’s assets locally by default, removing the need to explicitly design for application caching.


The cost and effort of hosting a server to deliver PWA Apps may be an issue for you, if it is then Packaged Apps have a clear advantage.

FeatureSigned AppsPWA Apps
Server requiredNoYes


FeatureSigned AppsPWA Apps
DiscoveryThrough MarketplaceThrough Marketplace and own site
Direct access using a URLNoYes


All apps need to be delivered to a user’s device, which will be affected by both the network bandwidth and the available storage memory on the device. Here the overall size of your app’s assets will be the primary decision driver, the larger your app the more likely you’ll want to deliver it as a PWA App.

FeatureSigned AppsPWA Apps
Marketplace review timeLonger (when using Signed APIs)Shorter
App updatesRequires a new package to be loaded onto MarketplaceCore app changes delivered on-the-fly, new install details (e.g. name, icon) require a new Marketplace package
App Asset/Content redundancy on devicePossibleNo, only used assets/content downloaded
App asset limitsPractical package size limit is device memory and network dependent, generally < 50Mb, <5Mb for low memory devicesOnline: No practical limit AppCached: As for Packaged Apps
Number of apps per deviceLimited by device memoryOnline: Practically unlimited AppCached: As for Packaged Apps
Asset extendibilityLimited, except for data from XMLHttpRequest and browser links all assets must be on the deviceUnlimited, within Origin
Remote contentBy using iframes, but that content will not have access to privileged APIs nor will it have the default CSP applied to it.By default


FeatureSigned AppsPWA Apps
Delivery standardProprietary (albeit a simple ZIP)Web standard
DebuggingEasier, no Origin limitationseasy, Just like normal web app debug
Reading JavaScript assetsRequires use of XMLHttpRequestDirect
Coding challengesOAuth functionality for Facebook, Dropbox, Twitter, etc.
Manifest must specify a launch_pathRequiredOptional
Apps per OriginDoesn’t applyDoesn't apply
mozApps API install functionApps.installPackageapps.install