How to block Arena

How to block Arena on every device

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

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Arena

Model hubs and developer platforms

arena.aiBlocked

3 hostnames in the Nullgen catalog

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

What Arena connects to

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

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

Block Arena in the browser

Free: Nullgen browser extension

The Nullgen extension stops typing and pasting into the Arena prompt box — and into AI prompt fields on any website, including new tools that launched last week. Everything else on the page keeps working. It runs right in Chrome, Edge, Firefox, and Safari, with no DNS or policy setup.

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Managed browsers: block the sites by policy

On a school or company fleet, push the hosts above as a browser policy to block the whole Arena site. These snippets use the official Chrome, Edge, and Firefox policy names.

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

Chrome and Edge treat a bare hostname as the host plus every subdomain.

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

Firefox needs both the apex and the wildcard pattern.

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Block the Arena app on phones and tablets

Nullgen mobile app

The Nullgen app blocks Arena 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.

Install iOS App Install Android App

Without Nullgen: Screen Time on iPhone and iPad

1Open Settings → Screen Time → Content & Privacy Restrictions and turn restrictions on. This covers Arena in Safari and in apps that use Apple’s web filter.
2Under Web Content, choose Limit Adult Websites — the setting that lets you deny arena.ai by name.
3Under Never Allow, add arena.ai. Safari and apps that use Apple’s web filter will refuse it.
4To keep the Arena 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 Arena can be blocked by site.
2Choose Only allow approved sites, or add arena.ai under Blocked sites.
3Under Controls → App limits, block the Arena app, or require approval for new installs from Google Play.

Block Arena on your home or school network

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

Subscribe to the Arena list

Every vendor, one list — on GitHub

AdGuard Home, uBlock Origin, and Brave rules

||arena.ai^
||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 Arena on managed devices

Schools and companies can block Arena 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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About Arena

How people use Arena

Arena, formerly LMArena, is the model comparison site that grew out of UC Berkeley’s Chatbot Arena research project. Users chat with two anonymous models side by side and vote on the better answer, which produces its public leaderboard. It runs at arena.ai, with lmarena.ai redirecting to it, and the original research domain lmsys.org is still live.

What makes Arena hard to block

Arena is in the catalog because it is a free, no-login way to use nearly every frontier model at once. The three domains are all listed, so the current site, the previous address, and the original project site are covered together.

Arena has no apps or API for end users, and nothing about it is embedded in other products, so the block is complete at the network or device level.

On a managed laptop, a browser policy or DNS block for the three Arena hosts stops the site from loading, and the browser extension stops typing into its prompt box. Arena needs no sign-in to chat, so the hostnames are the only control.

Questions about blocking Arena

Is Arena the same as LMArena?
Yes. LMArena became Arena in January 2026, and lmarena.ai now redirects to arena.ai. Both are listed, along with the original lmsys.org. Arena’s own announcement, dated January 2026, describes the rename.
Why block a research benchmark?
Because the site lets anyone chat with many frontier models without an account, which makes it an easy way around a block on the individual vendors. Arena’s site describes a leaderboard built from side-by-side votes.
Does Arena have an app?
No. It is a web product, and the listed domains cover it. Arena’s site has a leaderboard, a blog, and the comparison chat, all on arena.ai.
Does the free Nullgen extension block Arena?
Yes. The free extension blocks the prompt box on Arena and on any other site where it recognizes an AI prompt, in Chrome, Edge, Firefox, and Safari. It works on the page itself, so it needs no policy and no DNS change.
Does this block the Arena 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 Arena 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 Arena today

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

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