Trace the blocking layers
A gambling site is reached through a chain of steps, and every step is a place where a barrier can sit. Knowing those steps lets you place your own code where it does the most good, and recognise when an existing system feature already covers a gap better than a home-built layer could.
Where a request can be stopped
Follow one attempt from start to finish and the layers appear in order.
- The app or browser opens. System restriction settings can limit which apps can be installed or launched.
- The name is looked up. A hosts file or a filtering DNS resolver can refuse to return an address for listed domains.
- The connection is made. An on-device network filter, often built on a local VPN or content filter interface, can drop connections to listed hosts.
- The page loads. A browser extension can stop navigation to matching addresses inside that browser.
- An account is used. Licensed operators in many places offer self-exclusion, and some countries run wider self-exclusion schemes.
- Money moves. Some banks and card providers let customers block gambling transactions.
Compare the mechanisms side by side
| Mechanism | Where it acts | What it catches | Common gaps |
|---|---|---|---|
| Hosts file | Name lookup on one device | Exact listed hostnames | No wildcards, needs admin rights to change, bypassed by encrypted DNS in some browsers |
| Filtering DNS | Name lookup for a device or network | Listed domains and their subdomains | Other networks, private DNS settings, encrypted DNS chosen by apps |
| On-device network filter | Connections leaving the device | Traffic from most apps on that device | Platform limits on background work, conflicts with other VPNs, permission prompts |
| Browser extension | Inside one browser | Navigation in that browser and profile | Other browsers, private windows if not allowed, in-app browsers |
| App restrictions | Installing or opening apps | Dedicated gambling apps | Websites, apps already present, settings changed by the device owner |
| Payment blocks | Bank or card provider | Transactions coded as gambling | Other payment methods, and the setting is managed outside your app |
No single row covers everything, which is why a learning project usually combines one network-level layer with signposting to payment and self-exclusion options rather than trying to reinvent them.
Treat the blocklist as data
Keep domains in a separate, versioned file, not hard-coded. Normalise every hostname before matching: lower-case it, remove a trailing dot and convert internationalised names to their ASCII form so look-alike spellings do not slip through. Match the listed domain and every subdomain beneath it. Leave room for personal entries, because the sites that matter most to one person may not be on any shared list.
A static sketch of subdomain matching, shown for learning only:
// Illustrative only: does a hostname fall under a listed domain?
function isListed(hostname, list) {
let name = hostname.toLowerCase().replace(/\.$/, "");
while (name) {
if (list.has(name)) return true;
const dot = name.indexOf(".");
if (dot === -1) return false;
name = name.slice(dot + 1);
}
return false;
}
// list = new Set(["blocked-test.example"])If you use a shared list, check its licence, how it is maintained and how false positives are corrected.
Watch the side doors
Several ordinary features route around a single layer. Browsers can resolve names over encrypted DNS and ignore the system resolver. Phones switch between Wi-Fi and mobile data. Another VPN app can take over the network slot your filter relies on. In-app browsers inside social or messaging apps may behave differently from the main browser. None of this is unusual or suspicious; it is simply how modern devices work, and it is the main reason one layer is never enough.
Layer without overreaching
Blocking by hostname is enough for a personal blocker. Avoid designs that read the content of encrypted traffic, such as installing your own root certificate to inspect pages. That weakens the security of every connection on the device and creates far more risk than it removes. Two modest, well-understood layers, honestly described, protect better than one ambitious layer that breaks banking apps or leaks data.