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Agent402 Action Gate — Pre-flight Safety & Spend Validator
x402
Agent402 Action Gate — Pre-flight Safety & Spend Validator is a paid API for AI agents from agent402.tools, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-13).
Validates a proposed agent action (URL fetch, spend proposal, payload, and action description) for safety, prompt injection, spend authorization, and schema conformance before execution.
Price / call$0.01
Success—
StatusUnknown
How this service works
Deterministic preflight check for a proposed AI agent action - a tool call, payment, fetch, or write - before it executes. Evaluates up to four independent checks (prompt-injection scan on action text/untrusted text, URL/hostname validation, a bounded JSON-schema check on a payload, and a spend proposal against a spend mandate) and returns ALLOW, REVIEW, or BLOCK with stable reason codes plus a SHA-256 request/receipt hash pair.
Output
Returns a JSON object with a top-level `decision` field (ALLOW or DENY), a `checks` object with per-check results (url, spend, prompt, payload each with a status of pass/fail and optional details), an array of `reason_codes` explaining any failures, a SHA256 hash of the request for audit, and a receipt SHA256. Includes a `limitation` notice that ALLOW is a deterministic static result and does not guarantee downstream safety or successful execution.
Example use cases
Pre-flight check before USDC micro-payment
“Before my agent sends that 0.01 USDC pay-per-call to the external tool API, validate the spend proposal — amount is 1000 atomic units, asset is USDC, counterparty is the tool's address — and make sure the action description doesn't contain any prompt injection signals.”
Screening third-party API response for injection
“I just got a response back from an untrusted third-party endpoint and my agent wants to act on it — can you pass the raw text through the Agent402 action gate to scan it for prompt injection before my agent does anything with it?”
Schema conformance check on outbound payload
“My agent is about to POST a JSON payload to an external service — validate it against this bounded schema I've defined (type, required fields, no additionalProperties) and tell me if it passes before we send it.”
Technical details
Endpoint
POSThttps://agent402.tools/api/action-gateWhen to prefer
Choose this endpoint when your AI agent needs a deterministic, pre-execution safety gate before taking any action that involves spending USDC, fetching an external URL, or acting on untrusted third-party content. It is especially valuable in agentic pipelines where prompt injection from external sources is a risk, or where a spend mandate must be enforced before any payment is authorized. Prefer it over ad-hoc agent-side checks because it provides auditable SHA256 receipts, structured reason codes, and a single unified decision, all without requiring API keys or signup — the x402 wallet is the identity.
Side effects
- Spend proposal fails if amount_atomic or counterparty fields are malformed or exceed mandate limits — returns spend.status: fail with reason codes
- Prompt injection check flags untrusted_text or action.description containing known injection patterns — returns prompt.status: fail
- Payload fails if it does not conform to the provided bounded JSON schema — returns payload.status: fail
- URL check fails if the target URL is on a blocklist or malformed — returns url.status: fail
- Malformed request body (missing required fields or wrong types) returns a 4xx error
- BigInt parsing errors if spend amounts are passed as floats instead of integer strings
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| url | string | URL the action would fetch/call, if any |
| spend | object | {proposal:{amount_atomic,asset,counterparty}, mandate:{...}, now?} - checked with BigInt, no floats |
| action | object | {name, description, effect} - describes the proposed action; description is scanned for prompt-injection signals |
| schema | object | Bounded JSON-schema (type/required/properties/additionalProperties) to validate payload against |
| payload | object | Data the action would send, if any |
| untrusted_text | string | Any additional untrusted text to scan for prompt-injection signals |
Output
Schema · Response
{
"type": "json",
"example": {
"checks": {
"url": {
"status": "pass"
},
"spend": {
"status": "pass",
"allowed": true
},
"prompt": {
"status": "pass"
},
"payload": {
"status": "pass"
}
},
"decision": "ALLOW",
"limitation": "Deterministic static checks only. ALLOW does not guarantee safety, authorization, or successful execution.",
"reason_codes": [],
"receipt_sha256": "…",
"request_sha256": "…"
}
}Tags
x402
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