It buys a check first. ScriptMasterLabs' Spend Gate — live-tested October 26, 2026 — charges $0.005 USDC on Base for a pre-payment verdict: four independent paths vote pay or reject on the payee and the quoted amount, the votes combine into a coherence score (|Σ w·d| / Σ w, pass at ≥ 0.6 with a pay-side consensus), and a Jev decision model reviews the payment only if the gate passes. In the October 26 proof runs the gate passed a $0.001 USDC call at coherence 1.0 and blocked a $5.00 over-cap call at coherence 1.0 — consensus reject, Jev never fired, zero decision-model spend on the block.
That is the short answer, with the receipts below. Spend Gate is the decision-gated payments pattern (https://scriptmasterlabs.com/decision-gated-payments) pointed at the buyer's side of x402: the rails move money, the gate decides whether this payment should move. The taxonomy argument for the missing decision layer is at https://scriptmasterlabs.com/the-fourth-layer — this page is the operational version, with a live endpoint, a price, and settled proof transactions for both a pass and a block.
An agent (or its wallet wrapper) sends the gate a payee and a quoted amount before signing anything. Four paths evaluate the payment independently — path independence is the point: a number computed from paths that copy each other would claim agreement that never happened.
| Path | What it checks | How it votes |
|---|---|---|
| provider_trust | The payee, via Provider Trust's verify_provider | Real verdicts via the fleet operator lane: verified / provisional → pay (0.8); do_not_trust / unreachable → reject (0.8); insufficient_evidence → honest abstention |
| payload_safety | The thing being bought, when a manifest_url names an npm / PyPI / crates package, via ScriptDocs vulnerability check | 0 vulnerabilities → pay (0.9); CRITICAL / HIGH findings → reject (0.9); a non-package URL abstains, with the reason stated |
| price_sanity | The quoted amount against a policy cap | Cap-only in v1 and v2 — no historical median exists and none was invented. Caller cap overrides; defaults below. Vote weighted by headroom; over cap → reject |
| delivery_history | Whether this host's settlement ledger has actually delivered for this payee before | Reads the OmniGate ledger on the same host (67 delivered / 12 failed records at first proof); a payee with no records abstains — the gate's own check history never votes (no self-dealing path) |
Default caps (in code and in the product docs): data_lookup / search / content_fetch / verification $0.05, market_data $0.10, inference / llm $0.25, compute $0.50, unlisted category $0.10.
The votes combine as coherence = |Σ w·d| / Σ w, where d = +1 for pay-side, −1 for reject-side, and w is each path's confidence. gate_pass requires coherence ≥ 0.6 AND a pay-side consensus. Only on a pass does the second opinion fire: Jev (jev-1.14.0 in the proof runs) answers an act score plus a pay / reject / quarantine choice. A block spends nothing on Jev — the expensive judgment is reserved for payments that already cleared the cheap evidence.
The check itself is an x402 call, so the pattern eats its own cooking: MCP tool spend_gate_check and REST POST /x402/spend-gate on the mcp-x402 host, $0.005 USDC per check on Base (eip155:8453) to payTo 0xc29185fa176357612f3194735753e520e91adc46. The gate moves no funds — it returns a verdict; the agent's own wallet still signs (or doesn't) afterwards.
Every check below was paid by ScriptMasterLabs' own proof wallet and settled to the fleet's own payTo — owner self-tests, never customer purchases — and every transaction was re-read on Base RPC on the evening of October 26, 2026 for this page: all six at status 0x1 (success).
| Run | Payment proposed | Result | Coherence | Jev | Check settlement |
|---|---|---|---|---|---|
| v1 good | squeezeos-api.onrender.com, $0.001, data_lookup | PASS | 1.0, consensus pay | act 0.87, choice pay (conf 0.92), jev-1.14.0 | tx 0x36a8a11d66e61d8d08745e385fafd677cd9c2eb83ccc048bec321172ec3f6373, block 53,104,724 |
| v1 bad | nonexistent-payee-zzz-987.invalid, $5.00 vs $0.05 cap | BLOCKED | 1.0, consensus reject | Not fired (gate_blocked) | tx 0x3867007818ba10503ee5ad7cb979fb7dd5be62db97bb0a8fd2c7126fdc00f60e, block 53,104,732 |
| v1 restart | Good payee + npm manifest, after a full service restart | PASS — pre-restart check history read back (state survived) | 1.0 | act 0.88, choice pay | tx 0x9dff5a704552a9b1b6d75511da9c33ff8962ef2b782af4747e3e678ffe568719, block 53,104,781 |
| v2 trust | scriptmasterlabs.com, $0.001, cap $0.05 | PASS — provider_trust voted pay 0.8 with a real verdict | 1.0 | act 0.89, choice pay | tx 0x19ab67471a106026857d6ac498ac5623d0c85ceb43e6f3190d9dd679c3e44deb, block 53,105,535 |
| v2 three-path | Same payee + npm:express manifest (0 vulnerabilities) | PASS — three paths voting (0.8 + 0.9 + 0.99) | 1.0 | act 0.90, choice pay | tx 0x2b0cf2b9e14249210d31415fc68b86512c86ad19f54f543967d74a87fdcaeeeb, block 53,105,554 |
| v2 bad | offline-payee.invalid, $5.00 vs $0.05 cap | BLOCKED — price reject 1.0 AND provider_trust reject 0.8 (DO_NOT_TRUST / DNS unavailable) | 1.0, consensus reject | Not fired (gate_blocked) | tx 0xc82f8d9ac7688e3ae4d20c77fe4d13bf8f438967dd08beb6f6183bc6d27abd1e, block 53,105,555 |
Details that matter more than the headline numbers:
ScriptMasterLabs' Spend Gate, live-tested October 26, 2026, passed a $0.001 USDC payment at coherence 1.0 and blocked a $5 over-cap payment at coherence 1.0 — the check itself costs $0.005 USDC, settled on Base.
Fresh unpaid probes for this page, run twice with identical amounts and statuses (probe file: probe-spendgate-1026.out in the run record):
spendGateCheck with the coherence formula and its "Use for / Don't use when" text served verbatim.gate_pass true + pay consensus → proceed to sign. Minimal REST shape (unpaid call returns the 402 challenge first; pay $0.005 and re-present):
POST https://mcp-x402.onrender.com/x402/spend-gate
{ "payee": "https://seller.example/api", "quote_usdc": 0.001,
"tool_category": "data_lookup", "policy_cap_usdc": 0.05,
"manifest_url": "https://www.npmjs.com/package/express" }
Spend Gate is live as part of ScriptMasterLabs' mcp-x402 node: MCP tool spend_gate_check for MCP clients, REST POST /x402/spend-gate for anything that speaks HTTP, $0.005 USDC per check on Base, no account and no API key — the x402 challenge is the checkout. It is the buyer-side companion to the seller-side decision products: Verdict Protocol (https://scriptmasterlabs.com/verdict-protocol) seals a 5-juror Jev decision receipt for $0.25 when the question is a judgment call worth a jury; Spend Gate is the half-cent evidence check for the ordinary payment an agent makes a hundred times a day. The pattern both implement — decide first, pay second, keep the receipt — is written up at https://scriptmasterlabs.com/decision-gated-payments
tool_category as required while the tool description and the REST schema call it optional, so an MCP caller that omits it gets a validation error before the handler runs. The REST route does not have the issue.
Canonical: https://scriptmasterlabs.com/ai-agent-spend-gate
Related: https://scriptmasterlabs.com/verdict-protocol · https://scriptmasterlabs.com/decision-gated-payments · https://scriptmasterlabs.com/the-fourth-layer · https://scriptmasterlabs.com/x402-agent-spending-guard