Wallet-health pre-check

Before your first paid x402 call, check whether your wallet can actually complete it. A mined audit of this fleet found 44.9% of paid-path calls fail — and one silent cause is a wallet that cannot settle: no USDC on Base, or less than the endpoint's price. This check reads your balance before you pay and tells you plainly what is missing, instead of letting the call fail silently.

Wallet address (public address only — never a key, never a signature) Endpoint

Machine-readable: GET /clinic/wallet-check?address=0x…&slug=<slug>. Read-only: the check issues eth_call balance reads against Base mainnet — no keys, no signing, no transaction, nothing can be spent through it.

What a paid call actually needs

Requirement	Reality
USDC on Base	Required. At least the endpoint's price, held as USDC on Base (chain 8453, contract `0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`). USDC on Ethereum, Polygon or any other chain does not count.
ETH for gas	Not required. x402 settles via EIP-3009 `transferWithAuthorization`: you sign an authorisation, the facilitator submits it and pays the gas. This page shows your ETH balance for information only.
Token allowance / approval	Not required. EIP-3009 authorisations replace ERC-20 approvals — there is no approve transaction to send first.

Verdicts, plainly: ready — the balance covers the endpoint's price (the result says how many calls it covers). insufficient_funds — some USDC on Base, but less than the price; the exact shortfall is shown. no_usdc_on_base — zero USDC on Base; bridge or withdraw USDC onto Base first. invalid_address — the address is not 0x + 40 hex characters. Prices are the live catalogue prices (the same source as codegen); /brief currently shows its $0.01 loss-leader price until 2026-10-30.

Already paid and it still failed? Diagnose the failed payment by tx hash. Wondering what paying adds over the free trial? See the audited paid-vs-trial diff.