⚠ What this does NOT check
The format/checksum check only confirms the address is structurally valid: the right shape, and (where possible) a passing checksum. The optional on-chain check adds one more signal: whether the address has ever been used on that specific network, but neither one can tell you whether it's the correct recipient, whether it belongs to a scammer, or whether the exchange/wallet you're sending from actually supports that network. A technically "valid" and "active" address can still be the wrong one. Always send a small test amount first and confirm it arrives before sending the rest, the same rule as every guide on this site.
How this works: the format/checksum check runs entirely as JavaScript in your browser: the address is never sent to a server, logged, or stored anywhere. The optional "Check on-chain activity" button is different: clicking it sends the address directly from your browser to a public blockchain node (e.g. a public Ethereum or Solana RPC provider) so it can look up whether that address has been used. Nothing is sent unless you click that specific button, and it still never touches a PlainCrypto server. Full detail in the Privacy Policy. Don't take our word for it: right-click → "View Page Source" to read the exact code yourself (see Our Promises).