Working examples that call https://mcp.chainhelix.io/ and pay per tool call. No account, no signup - a funded wallet is the whole integration.
Networks you can pay on: Base (USDC over x402) and BNB Smart Chain (U, USD1, USDT, USDC over Binance b402). Prices are 1 to 25 cents per call; the current price list is in every 402 response.
| template | what it shows |
|---|---|
js-x402-fetch/ |
The standard client (@x402/fetch, x402 v2). Five lines of payment code. Start here. |
js-pay-per-call/ |
The whole protocol hand-rolled in one file (viem): 402 -> sign EIP-3009 -> retry. Base and BNB Smart Chain with one flag. |
python-pay-per-call/ |
Same flow in Python (eth-account + requests). |
Try the free tools first - they need no payment and let you check our record
before spending anything: proof_spec, list_reveals, verify_reveal,
attestation_stats. Every paid signal is committed on chain before its outcome
exists and revealed 72 hours later.
Payment safety, as implemented server-side: you are charged only when a payment settles; a settled payment whose response you never received is redeemable for 24 hours by re-sending the identical payment header - never a second charge.
Notes
- The hand-rolled templates sign EIP-3009 (gasless). On BNB Smart Chain that covers U and USD1; USDT and USDC there use permit2-exact (one-time on-chain approval to the Permit2 contract, then gasless).
- Verified against the live endpoint: all three templates run the full flow to the facilitator's on-chain funds check with an unfunded key (refused for funds only). Fund the wallet and the same code returns tool results.