x402 proves payment. It doesn't prove trust — so we built Vouch

x402 proves payment. It doesn’t prove trust — so we built Vouch
Payment answers “who paid?”
Trust answers “should I serve them?”

If you run an x402 API, that gap is the whole product risk. ERC-8004 gives agents an identity and reputation surface on-chain — useful, but still Sybil-prone if you treat raw feedback as credit. We built Vouch: a trust layer that returns a 0–100 score and an ALLOW / WARN / BLOCK recommendation for gateways that need a decision before they hand over paid content.

And the risk runs both ways. The agent sending the payment has the mirror problem: is the wallet on the other side of this 402 a real service, or a burner that will take the USDC and vanish? So Vouch now scores both sides: payer trust for API providers, payee trust for paying agents.

This post is a build-in-public snapshot of Vouch on Base.

The flows we care about
Seller side — should I serve this payer?
Client → x402 payment verification → Vouch payer check → your route
↘ optional settlement attest
Buyer side — should my agent pay this wallet?
Your agent → Vouch payee check → x402 payment → their API
Seller side:

x402 middleware verifies payment and yields a payer wallet
Your gate calls Vouch GET /v1/wallets/{payer}/score
On BLOCK, return 403 before the expensive handler
After allow, optionally POST /v1/payments/x402 so settlement history strengthens future scores
Buyer side:

Your agent hits a 402 and extracts the payee wallet from the payment requirements
It calls GET /v1/payees/{payee}/score before signing anything
On BLOCK, skip the payment; on WARN, apply your own policy (cap the amount, require a human, whatever fits)
Sample seller-side middleware lives in the repo: examples/x402-trust-gate.

What goes into a payer score (today)
Signal Role
ERC-8004 identity Registered agent + metadata URI presence
ERC-8004 reputation Feedback volume / average, with Sybil dampening
Wallet heuristics Age, activity, burner patterns, funder clusters
Manual WL/BL Per-customer policy (after the chain score)
x402 settlements Attested payment history (10% weight — still accumulating data)
Recommendations: roughly ≥70 ALLOW, 40–69 WARN, <40 BLOCK (blacklist / high Sybil risk forces BLOCK). Scores are informational — not a guarantee or credit rating.

Owner-index lag is surfaced as dataCoverage so integrators can see freshness instead of assuming omniscience.

New this week: the Payee Trust API
GET /v1/payees/{address}/score answers the buyer-side question with a different signal mix, because a payee's failure mode isn't Sybil feedback — it's taking money and disappearing:

Signal Role
Receiving history Attested x402 settlements where this wallet was the payee — count, active days, distinct payers
Wallet health Same age / tx-count / burner heuristics as the payer score
Drain pattern Exit-scam shape: received funds, then pulled out (near-)everything — checked over native ETH and Base USDC, with dust floors so gas residue doesn't false-positive
Outcome history Prior confirmed-fraud / confirmed-legitimate labels naming this wallet
Two design details worth calling out:

It never 404s. A wallet nobody has attested yet still gets a 200 with dataDepth: "thin", and the weights shift accordingly — a thin-data wallet is judged mostly on wallet health and drain shape, a rich one mostly on its receiving track record. You decide how much confidence a thin score deserves; we don't pretend to know more than we do.
The data loop is shared. Every POST /v1/payments/x402 attestation is now verified on-chain (fail-closed) and credits both sides: the payer's settlement history and the payee's receiving history. Sellers attesting payments are, as a side effect, building the dataset that protects buyers.
API surface (integrator path)

Score a payer wallet (seller side, primary x402 path)

curl -H "Authorization: Bearer $VOUCH_API_KEY" \
https://agent-trust-tawny.vercel.app/api/v1/wallets/0xYOUR_PAYER/score

Score a payee wallet (buyer side, before your agent pays)

curl -H "Authorization: Bearer $VOUCH_API_KEY" \
https://agent-trust-tawny.vercel.app/api/v1/payees/0xTHEIR_WALLET/score

Attest a verified payment (idempotent on txHash)

curl -X POST -H "Authorization: Bearer $VOUCH_API_KEY" \
-H "Content-Type: application/json" \
-d '{"wallet":"0xYOUR_PAYER","txHash":"0x...","resource":"/api/premium"}' \
https://agent-trust-tawny.vercel.app/api/v1/payments/x402
Also available: agent-ID scoring, batch scores, outcome reporting (POST /v1/events/{id}/outcome — tell us what actually happened after a verdict), MCP tools (check_wallet_trust, attest_x402_payment), and a TypeScript client on npm: npm install @vouchscore/sdk (MCP server: @vouchscore/mcp-server). The SDK and MCP server don't cover the payee endpoint yet — next on the list, along with a spend-policy helper for agent runtimes.

Design choices we won’t apologize for
Fail closed on wallet binding / critical RPC failure when verifying binders — better a 502/BLOCK than a silent ALLOW.
Attestations are verified on-chain before they count — a well-formed wallet + txHash isn't enough to fabricate settlement history; the tx must be real, successful, and attributable to the claimed wallet.
Whitelist is not a Sybil free pass — high Sybil risk refuses to promote WARN→ALLOW.
Free anonymous public scoring stays frozen — API key required for every score; we want real integrators, not scrape farms.
x402 settlement weight starts small (10%) — data must accumulate before it deserves more.
Every score explains itself — the response ships a breakdown of the four weighted components (identity / reputation / wallet / x402), each with its score, weight, and contribution, so a gateway can log why a verdict was what it was, not just the number.
Try it
Built for x402 API providers (payer gating + settlement attestation) and agent-runtime builders (payee screening before your agents spend).

Sign up: agent-trust-tawny.vercel.app/signup — free account, no invite code
SDK: npm install @vouchscore/sdk
Code & docs: github.com/kzmttkc/agent-trust
Guides: docs/x402-integration.md, docs/mcp-setup.md, docs/openapi.yaml
Building something in this space? Reply here or DM — happy to compare notes.

Built with Next.js, viem, Neon, and the ERC-8004 registries on Base. Tagline: trust layer for agent commerce.