Glossary

Progressive Web App

A PWA can offer installation, faster repeat loads, and limited operation without a network. These capabilities require secure HTTPS, a considered caching strategy, and respect for differences in browser and device support.

Short definition

A website enhanced with device capabilities and a deliberately managed offline path.

A PWA uses standard web technologies—HTML, CSS, JavaScript, and HTTP(S). A web app manifest describes its name, icons, and display mode when installed. A service worker runs separately from the page and can intercept a request, serve a pre-cached resource, or return an offline fallback.

Not every PWA works entirely offline, and merely registering a service worker does not make an application faster or more secure. The design must determine which resources can be stored safely, how to establish whether data is current, and how to explain limitations to users while they are offline.

The problem it solves

A more resilient website on unreliable networks and an easier return to the application

A PWA is suitable where users repeatedly open the same work tool or where limited connectivity has a practical impact.

an inventory application used on a mobile device in a warehouse with an unreliable network
an internal work tool that can be added to the home screen and opened independently
a public catalogue with safely cacheable static resources and an offline explanation
a form that can preserve local work in progress and submit it safely later
limited push notifications where users expect them, give consent, and the platform supports them

Practical example

An inventory application works through a brief loss of connectivity

A worker installs the application on a device. The service worker stores the application shell and a view of the most recently synchronised list. If the network drops, the application clearly indicates that the data may be out of date and permits an unfinished operation to be stored only in a secure local queue record.

When the client comes back online, it does not declare the operation complete merely because it was stored locally. It sends it to the server with an identifier for idempotent processing, and the server rechecks authentication, permissions, and the current inventory state. A conflict is shown as an issue to resolve, not as a silent overwrite.

JSON – web app manifest

{
  "name": "Skladová aplikace",
  "start_url": "/sklad",
  "display": "standalone",
  "icons": [{ "src": "/icons/app-192.png", "sizes": "192x192", "type": "image/png" }]
}

How it works

From opening a website to a controlled offline fallback

A service worker is a separate script with its own lifecycle. It must be updated and tested as carefully as any other operational part of the application.

HTTPS and the manifest The application is available over HTTPS and the manifest gives the browser metadata for possible installation.
Service worker registration The page registers a script that installs and activates according to its own lifecycle.
Caching selected resources The service worker can pre-cache the application shell or resources that are safe to cache, but not every response indiscriminately.
Request and offline decision For a request, it selects a strategy: network, cache, a combination, or a comprehensible offline fallback.
Updates and synchronisation A new worker version activates in a controlled manner. When the client returns online, the server must revalidate data changes and resolve any conflict.

Key concepts

Manifest, service worker, and cache versions

A PWA is not a switch. Individual capabilities can be added progressively, and their availability must be verified on target devices.

Web app manifest

A JSON file containing a name, icons, start URL, and display mode. It supports installation but does not create an offline mode by itself.

Service worker

A script running outside the page that can respond to requests and manage a cache. It has its own lifecycle and should not handle sensitive data without defined limits.

Offline fallback

A deliberately designed state without a network: it can display stored content, a limited interface, or clear information that an action cannot be completed.

Updates

A new worker may not take effect immediately in every open tab. The application must offer a refresh in a way users can understand.

Push and synchronisation

These require platform support, user permission, and precise reasons for use. They are not a necessary part of every PWA.

Benefits and limitations

Better resilience in exchange for managing versions, caches, and conflicts.

Benefits

installation and quick return to a frequently used work tool
an offline fallback or availability of selected static resources
less dependence of repeat loads on network quality
progressive addition of capabilities without leaving web standards

Risks and common mistakes

an old service worker returns outdated code or content
sensitive or personalised data is cached without a clear security model
assuming that a service worker automatically makes everything available offline
conflicting changes made without a network
ignoring differences in support for installation and push notifications across platforms

When it makes sense

When limited offline operation or installation meets a genuine user need.

A PWA is suitable for a frequently used internal tool, inventory application, or catalogue where an offline fallback offers concrete value. A safe starting point can be small: a manifest, fast static resources, and a clear offline page, rather than complex synchronisation of edits from the outset.

If an application does not operate offline and users open it only rarely, a PWA may not offer enough benefit to justify testing caches and updates. Its greater value comes from useful scenarios, not from an icon on the home screen.

What to consider

Offline mode must tell the truth about data availability and age.

A PWA is an operational part of the application. Caching and synchronisation require the same attention as a backend integration.

test first installation, worker updates, cache deletion, and transitions between online and offline
show whether data is current, stored locally, or waiting for synchronisation
do not cache sensitive data without a defined key, expiration, and access model
verify actual support in target browsers and provide a functional conventional web path
recheck authentication, authorization, and business rules on the server when returning online

Common questions

PWAs in practice

Is a PWA a native mobile app?

No. It is a web application that can use some device capabilities and offer installation. Support and access to device features vary by browser and operating system.

Will everything work offline after I add a service worker?

No. A service worker only makes it possible to manage requests and caches. The offline scenario, data, errors, and subsequent synchronisation must be designed and tested.

Can a PWA cache orders and permissions?

Only with a very careful security model. A cache is not a source of truth, and sensitive personalised content must not be accidentally exposed to another user or allowed to become stale.

Do I need HTTPS for a PWA?

Yes. Under normal conditions, a service worker is available only in a secure context. HTTPS alone does not address authorization, data security, or the correct caching strategy.

How I approach application operations in practice

I design offline behaviour and caching around data that can be deferred safely.

For web and integration systems, I evaluate the value of installation, caching, and synchronisation together with data security and users’ real conditions.

How I approach application architecture Discuss your project without obligation