Is this RPC actually Arc?
A chain ID is a label your wallet writes on the tab. The RPC decides which chain you are talking to. Paste an endpoint and this page asks it the questions Circle's published genesis lets us ask. It only ever reads. Nothing is signed and no wallet is connected.
Your browser sends read-only JSON-RPC calls straight to that server. If the server does not allow browser requests the check fails with a network error rather than a verdict; that is a limitation of the browser, not evidence about the chain. The testnet endpoint is pre-filled because it is the only public Arc RPC as of 4 September 2026.
What this can and cannot prove
methodIt can prove that an endpoint answers with the chain ID it claims, that it is producing blocks at roughly Arc's cadence, that USDC's system contract exists at Arc's reserved address, and, for chain 5042, whether block zero carries the coinbase and the 12 May 2026 timestamp that Circle's published mainnet genesis specifies.
It cannot prove that the endpoint is Circle's chain rather than a fork of it. A fork of the public genesis passes every one of these tests. The only thing that settles identity is comparing the endpoint's block-zero hash against the hash of Circle's genesis as served by Circle's own RPC. That RPC is not public yet. The day it is, this page will pin the hash and compare against it.
What to do instead: pull the genesis yourself from circlefin/arc-node, add the network only from an official source, and confirm any balance on a second, independent reader before you act on it.