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SpendPreflight
x402
SpendPreflight is a paid API for AI agents from api.spendpreflight.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-12).
Pre-authorizes AI agent payments by evaluating x402 PaymentRequired responses or carts against configurable spending rules, returning an allow/hold/block decision with the cheapest acceptable payment option and a receipt ID.
Price / call$0.02
Success—
StatusUnknown
How this service works
Operated by SpendPreflight: sanctions screening and allow/hold/block preflight for x402 payments.
Output
A JSON object containing: a 'decision' field (allow, hold, or block), a 'reasons' array explaining the decision in plain language, the cheapest acceptable payment option from the provided x402 body, and a 'receipt' object with a unique ID, timestamp, decision, and SHA-256 hash of the input for audit purposes.
Example use cases
Capping autonomous agent daily spend
“My AI agent is about to make a payment — run a preflight check on this x402 PaymentRequired body with a $10 per-payment max and a $100 daily cap, and let me know if it should be allowed, held, or blocked.”
Blocking unknown merchant domains
“Before my agent pays this invoice, screen the x402 response and block it if the domain is newer than 14 days on my allowlist — I only want it to pay trusted sites I've seen before.”
Finding cheapest option in a multi-option payment
“I received a x402 PaymentRequired with multiple payment options — run a preflight check with no special rules and just tell me which option is cheapest and whether it's safe to pay.”
Technical details
Endpoint
POSThttps://api.spendpreflight.com/v1/preflight?utm_source=zero.xyzWhen to prefer
Use this endpoint before every AI agent payment to enforce spending guardrails without risking funds — it is read-only and never signs or settles transactions. Prefer it over manual rule checks when your agent handles x402 PaymentRequired responses or needs auditable receipts for every payment decision. It is especially valuable when running autonomous agents with real budgets, needing daily caps, per-payment limits, domain allowlisting, or hold-for-review workflows before committing USDC.
Side effects
- Malformed or missing x402 PaymentRequired body returns a validation error
- Unsupported x402 version (not v1 or v2) may cause parsing failure
- Conflicting rules (e.g. per-payment max lower than minimum network fee) may always return block
- If the daily cap has already been reached, all payments will be blocked regardless of amount
- Domain age rules may block legitimate new merchants not yet on the allowlist
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"reasons": [
"allow: all rules passed"
],
"receipt": {
"id": "…",
"ts": "…",
"decision": "allow",
"input_sha256": "…"
},
"decision": "allow"
}
}Tags
x402
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