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Concepts

Payments

x402 setup for paid discovery workflows. You do not need payment setup for the free tier, GET /health, descriptors, docs, or GET /verify.

How x402 works

x402 turns HTTP's long-reserved 402 Payment Required status into a working payment flow: the API quotes a price, your agent pays in-band, and the request completes. No account, no API key, no checkout page.

No blockchain knowledge required — the CLI and x402 client libraries handle the full payment exchange automatically. Payments are in USDC — a stablecoin pegged 1:1 to the US dollar — on the Base network, so prices are dollar prices: $0.002 per discovery workflow.

The automatic flow

  1. Your agent calls POST /discover as normal.
  2. If the free tier is exhausted, Sigildex responds 402 Payment Required — the x402 challenge rides in the PAYMENT-REQUIRED response header, and the machine-readable terms (price, asset, network, pay-to address) are published at /.well-known/x402.json.
  3. Your x402 client signs a USDC payment authorization for the quoted price and retries the same request with the payment-signature header.
  4. Sigildex verifies the payment, serves the response, and settles on Base. Failed application responses are never settled — you do not pay for errors.
Your agent SIGILDEX Base · USDC 1 POST /discover 2 402 + payment requirements 3 retry + payment-signature settle $0.002 USDC 4 200 ranked results
The x402 payment loop: challenge, pay, retry, settle.

What you need

  • Nothing, for the free tier (50 discovery workflows per day per IP), GET /verify, GET /health, descriptors, and docs.
  • For paid discovery: an EVM wallet key holding USDC on Base — SIGILDEX_WALLET_KEY for the CLI, or an x402 client library in your application.
  • Machine-readable terms: /.well-known/x402.json. Sigildex settles through the Coinbase Developer Platform facilitator; the open protocol lives at x402.org.

Pricing

  • 50 discovery workflows per day per IP are free.
  • After the free tier, discovery workflows cost $0.002 USDC on Base.
  • A workflow is one /discover call plus up to 5 free /inspect calls using the returned query_id.
  • /verify is free and never returns a payment challenge.

Auto-pay


export SIGILDEX_WALLET_KEY=<your-evm-private-key>
npx @sigildex/cli search "browser automation" --json

The CLI uses x402 to sign and retry paid requests when a wallet key is configured. For application integrations, fetch /.well-known/x402.json and handle the payment challenge returned by paid endpoints.

Headers

Paid requests use payment-signature. Responses include X-Sigildex-Version and X-Request-Id; discovery responses also include rate-limit headers.

Errors

PAYMENT_REQUIRED means the free discovery tier is exhausted and a valid payment is needed. PAYMENT_FAILED means payment verification failed. PAYMENT_UNAVAILABLE means the payment system is temporarily unavailable. No settlement occurs for failed application responses.