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x402 Doctor Preflight Check
x402
x402 Doctor Preflight Check is a paid API for AI agents from x402-doctor.fizzl.eu, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-12).
Pre-flight safety check for an x402 payment endpoint — returns go/caution/no_go verdict, recommended payment option, and reasons before your agent pays anything
Price / call$0.001
Success—
StatusUnknown
How this service works
Is this x402 endpoint safe to pay? Check it before your AI agent pays: go / caution / no_go, the recommended payment option, and why (payment would fail, over your budget, price above advertised, not HTTPS, unknown token). Never pays the endpoint. Cached 10 min.
Output
Returns a JSON object with: a verdict enum (go, caution, or no_go), a safe_to_pay boolean, a human-readable summary, an array of payment options each with USD cost, network, asset symbol, payable status, and any problems found, a recommended_option index, and a reasons array with level (no_go/caution/info), code, and message for each issue detected. Results are cached for 10 minutes.
Example use cases
Budget guard for autonomous agent
“Before my agent pays anything at https://ai-service.example.com/generate, check if it's safe — my max budget per call is $0.02 and I want to pay on the Base network (eip155:8453).”
HTTPS and token legitimacy check
“Can you verify that this x402 endpoint https://data-api.xyz/premium is using HTTPS and a recognized token before I let my agent call it?”
Advertised price mismatch detection
“I was told this endpoint https://api.coolservice.io/search costs $0.001 per call — can you do a preflight check to make sure the actual price matches what was advertised before my agent pays?”
Technical details
Endpoint
GEThttps://x402-doctor.fizzl.eu/api/v1/preflight?utm_source=zero.xyzWhen to prefer
Use this endpoint whenever an AI agent is about to make an x402 payment and needs a safe, non-paying preflight check first. It is specifically designed for the x402 protocol and understands CAIP-2 networks, USD budget limits, HTTPS requirements, and known token validation — making it far more appropriate than a generic HTTP probe or manual inspection. Prefer this over the sibling debug endpoint when you want a quick go/no-go decision rather than a deep diagnostic of a broken endpoint.
Side effects
- URL is missing or malformed — returns error without verdict
- Target endpoint is unreachable — may surface as caution or no_go with connectivity reason
- x402 header parsing failure if target returns malformed 402 response
- Budget exceeded — verdict is no_go with over_budget reason code
- Non-HTTPS endpoint — verdict is no_go with reason code for missing HTTPS
- Unknown or unsupported token — flagged as caution or no_go
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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