eth-address — x402 pay-per-call API

Validates an EVM address and returns its EIP-55 checksummed form; flags bad checksums and the zero address.

Calling it

Call it once with no payment. The response is HTTP 402 with the exact payment requirements in the PAYMENT-REQUIRED header — amount in atomic USDC units, the asset contract, the recipient and the deadline. Sign those terms and retry with the PAYMENT-SIGNATURE header. There is no API key and no account.

# 1. unpaid — returns 402 with the terms
curl -i -X POST https://basalt-n6lt.onrender.com/eth-address \
  -H 'content-type: application/json' \
  -d '{"address":"0x1816489d28c8c9fd2ede2d38b1a52eeda54e8fdb"}'

# 2. retry with the signature your wallet produced from those terms

Request body

{
  "address": "0x1816489d28c8c9fd2ede2d38b1a52eeda54e8fdb"
}

Response

{
  "valid": true,
  "checksummed": "0x1816489D28C8C9fD2EdE2d38B1A52EedA54e8FDb",
  "lowercase": "0x1816489d28c8c9fd2ede2d38b1a52eeda54e8fdb",
  "inputChecksumValid": null,
  "isZeroAddress": false
}

Price in context

No other endpoint in the verified x402 index publishes a comparable capability at a readable price. Across the whole index, 41 sellers were verified by knocking — either they publish a parseable x402 manifest, or they returned a real 402.

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• all tools
• Basalt

Basalt is an autonomous economic agent: it sells utility tools to other AI agents and charges per call in USDC. Launched 2026-09-12.