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Add Second Opinion (adversarial verification API) to Ecosystem #536

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Expand Up @@ -39,6 +39,7 @@ x402 is an emerging open standard from the Coinbase ecosystem focused on safer,
- [Strale](https://strale.dev) - Business data & compliance APIs for AI agents. 250+ quality-scored capabilities (company data, VAT validation, sanctions screening, KYB) across 27 countries with x402 payment support. [MCP server](https://www.npmjs.com/package/strale-mcp) available.
- [Hedera and the x402 Payment Standard](https://hedera.com/blog/hedera-and-the-x402-payment-standard/) - Hedera ecosystem overview of x402-style programmable payments for applications and AI agents.
- [CardZero](https://cardzero.ai) - Smart-contract wallet (ERC-4337) for AI agents on Base mainnet, USDC. Buyer-side x402 support via `POST /v1/x402/pay`. Owner-controlled spending rules (per-tx limit, daily cap, whitelist, freeze) enforced on-chain. Also runs first known production deployment of ERC-8004 + ERC-8183.
- [Second Opinion](https://secondopinionx402.com) - Adversarial verification API for AI agents: an independent skeptic attempts to refute a claim before the agent acts on it, returning a structured verdict with calibrated confidence, citations, and an Ed25519-signed receipt. Pay-per-verdict via x402 ($0.03–$0.75 USDC) on Algorand, Base, and Solana; free trial in the browser (no wallet); no account or API key; zero-install hosted MCP connector for agent stacks; `pip install secondopinion-x402` for LangChain/CrewAI. ([MCP](https://secondopinionx402.com/mcp) | [Benchmark](https://secondopinionx402.com/benchmark))

### Facilitators & Networks
- [Coinbase Hosted Facilitator (Base)](https://docs.cdp.coinbase.com/x402#offload-your-infra)
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