Buyer-side payment firewall
Buyer-side payment firewall: should THIS agent make THIS payment now? Where /api/assess vets the seller, this vets the payment against your own agent's behaviour. POST {agent_id, payment:{payto_address,amount,resource_url}, context?:{untrusted_text,intended}, policy?} returns allow/hold/block plus 9 signals incl. routing_anomaly, velocity, amount_anomaly, injection_destination, intent_mismatch. Stateful per agent_id.
Answeringour last check, 2026-09-24
1 of 1checks answered this week
71 msmedian answer time
$0.002listed price per call
$0.002price it asked us
Paid test badge: not yet. The checks above are free: we call the tool without paying and read the payment request it sends back. The Verified badge needs paid calls whose answers match the promised output, and nobody can buy a badge.
Endpoint
POST https://402sentinel.com/api/firewall
| Category | Everything else |
|---|---|
| Provider host | 402sentinel.com |
| Networks | eip155:8453, solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp |
| Payment schemes | exact |
| Self-reported calls, 30 days | 1 from 1 payers (the provider's figure, not ours) |
Our checks, last 30 days
| Day | Result | HTTP | Asked | Time |
|---|---|---|---|---|
| 2026-09-24 | valid payment request | 402 | $0.002 | 71 ms |
Example input (from the provider)
{
"body": {},
"bodyType": "json",
"method": "POST",
"type": "http"
}
Promised output schema (from the provider)
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"properties": {
"input": {
"additionalProperties": false,
"properties": {
"body": {
"properties": {
"agent_id": {
"description": "The calling agent's wallet (keys per-agent history). Optional \u2014 auto-filled from the x402 payer if omitted.",
"type": "string"
},
"context": {
"description": "Where the payment instruction came from (provenance).",
"properties": {
"expected_payto": {
"description": "The payTo the agent intended, to detect routing swaps.",
"type": "string"
},
"metadata": {
"type": "object"
},
"source": {
"description": "e.g. \"tool_output\", \"web_content\".",
"type": "string"
}
},
"type": "object"
},
"payment": {
"description": "The payment instruction being vetted.",
"properties": {
"amount": {
"type": "number"
},
"asset": {
"description": "e.g. \"USDC\"",
"type": "string"
},
"payto_address": {
"description": "Address the payment would go to \u2014 0x EVM (Base) OR base58 Solana.",
"type": "string"
},
"resource_url": {
"description": "The resource being paid for.",
"type": "string"
}
},
"required": [
"payto_address"
],
"type": "object"
},
"policy": {
"description": "Optional checks, e.g. {check_counterparty: true}.",
"type": "object"
}
}
},
"bodyType": {
"enum": [
"json",
"form-data",
"text"
],
"type": "string"
},
"method": {
"enum": [
"POST"
],
"type": "string"
},
"type": {
"const": "http",
"type": "string"
}
},
"required": [
"type",
"method",
"bodyType",
"body"
],
"type": "object"
}
},
"required": [
"input"
],
"type": "object"
}