How to block LMArena

How to block LMArena on every device

LMArena is the chatbot arena that offers free, no-login access to nearly every frontier model side by side. Below: how to block LMArena in the browser, on phones and tablets, on your home or school network, and on managed devices.

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LMArena

Model hubs and developer platforms

lmarena.aiBlocked

2 hostnames in the Nullgen catalog

Every entry also covers its subdomains, so the LMArena app and API are blocked too.

What LMArena connects to

These are the hostnames LMArena uses for its website, its apps, and its API. Each entry is matched as a suffix — blocking lmarena.ai also blocks every subdomain of it — so the LMArena app cannot slip through on a hostname that is not listed. Shared hosts that other products need are deliberately left out.

Hostnames blocked for LMArena
Hostname	Role
lmarena.ai	Main website
lmsys.org	App, API, or content host

Block LMArena in the browser

Free: the Nullgen browser extension

The free extension blocks LMArena and every other tool in the catalog in Chrome, Edge, Firefox, and Safari. It works on the page itself — no DNS change, no policy — and updates as the catalog grows.

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Managed browsers: block the sites by policy

On a school or company fleet, push the hostnames as a browser policy so LMArena is blocked even when someone uninstalls extensions. These snippets use the official Chrome, Edge, and Firefox policy names and the same hosts listed above.

Chrome and Edge — URLBlocklist

{
    "URLBlocklist": [
        "lmarena.ai",
        "lmsys.org"
    ]
}

Firefox — policies.json

{
    "policies": {
        "WebsiteFilter": {
            "Block": [
                "*://lmarena.ai/*",
                "*://*.lmarena.ai/*",
                "*://lmsys.org/*",
                "*://*.lmsys.org/*"
            ]
        }
    }
}

Chrome and Edge treat a bare hostname as the host plus every subdomain. Firefox needs both the apex and the wildcard pattern.

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Block the LMArena app on phones and tablets

Nullgen mobile app

The Nullgen app blocks LMArena and 100+ other AI apps and sites on the whole device with an on-device filter — the app, the website, and the API, on any network, with no DNS server to run. Included with Nullgen Pro.

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Without Nullgen: Screen Time on iPhone and iPad

1Open Settings → Screen Time → Content & Privacy Restrictions and turn restrictions on. This covers LMArena in Safari and in apps that use Apple’s web filter.
2Under Web Content, choose Limit Adult Websites — the setting that lets you deny lmarena.ai by name.
3Under Never Allow, add lmarena.ai. Safari and apps that use Apple’s web filter will refuse it.
4To keep the LMArena app off the device entirely, delete it and set Installing Apps to Don’t Allow, or use Ask to Buy on a child’s Apple Account.

Without Nullgen: Family Link on Android

1Open Family Link, choose the child, then Controls → Content restrictions → Google Chrome — where LMArena can be blocked by site.
2Choose Only allow approved sites, or add lmarena.ai under Blocked sites.
3Under Controls → App limits, block the LMArena app, or require approval for new installs from Google Play.

Block LMArena on your home or school network

A DNS blocker such as Pi-hole, AdGuard Home, NextDNS, or pfBlockerNG blocks LMArena for every device on the network — laptops, phones, consoles, and the LMArena app — without installing anything on them. Subscribe to the LMArena file from the public blocklist, or paste the rules directly.

Subscribe to the LMArena list

Every vendor, one list — on GitHub

AdGuard Home, uBlock Origin, and Brave rules

||lmarena.ai^
||lmsys.org^

DNS blocking cannot see inside a VPN or a phone on mobile data. For a block that follows the device, use the Nullgen apps or an MDM profile.

Block LMArena on managed devices

Schools and companies can block LMArena on every managed iPhone, iPad, laptop, and Chromebook from the MDM they already run — Intune, Jamf, Kandji, or Google Workspace — with per-person policies and an approval flow for legitimate use. Nullgen Pro provides the profiles and the dashboard; these guides walk through the setup.

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Questions about blocking LMArena

Does the free Nullgen extension block LMArena?
Yes. The free extension blocks prompts on LMArena and every other AI tool in the catalog in Chrome, Edge, Firefox, and Safari. It works on the page itself, so it needs no policy and no DNS change.
Will blocking LMArena break other websites?
No. Every hostname on this page belongs to LMArena alone. Shared websites that other products depend on are never on the list — which is also why AI features built into those products stay reachable.
Can someone get around a LMArena block?
A browser-only block can be bypassed with another browser or the LMArena app, and a network block can be bypassed with a VPN or a phone on mobile data. A block on the device itself — the Nullgen apps, Screen Time, or an MDM profile — follows the device wherever it goes.
Does this block the LMArena app, not just the website?
A DNS or device-level block does. The app talks to the same hostnames listed above, and every entry covers its subdomains, so the app cannot slip through on a hostname that is not listed. A browser policy or extension only covers the browser.
What happens when LMArena adds a new hostname?
The catalog is updated as vendors change, and the Nullgen apps, the extension, and the public blocklist all read from it, so a new hostname reaches every device without anyone editing a list by hand.

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Block LMArena today

Start with the free browser extension. Add Nullgen Pro when you need the LMArena app blocked on phones, tablets, and desktops, with approvals for the people who really need it.

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