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PennyRail JSON Key Lister
x402
PennyRail JSON Key Lister is a paid API for AI agents from pennyrail.vercel.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).
Extracts and returns a flat list of all top-level keys present in a given JSON object
Price / call$0.001
Success—
StatusUnknown
How this service works
Machine-readable settlement service
Output
A JSON object containing a list of all top-level key names extracted from the provided input object. The response is machine-readable and enumerates each property name present at the root level of the submitted JSON.
Example use cases
Inspect unknown API response structure
“I got back this JSON from an API and I'm not sure what fields it contains — can you list all the keys so I know what I'm working with: {"id": "abc123", "ts": 1700000000, "payload": {}, "status": "ok"}?”
Validate expected fields in JSON payload
“Can you pull out all the top-level keys from this JSON so I can check whether the required fields like 'userId' and 'amount' are present: {"userId": "u99", "amount": 42, "currency": "USD"}?”
Document JSON schema from live data
“I'm writing documentation and need to know every key this JSON object exposes — can you enumerate them for me: {"product": "Widget", "sku": "W-001", "price": 9.99, "inStock": true, "tags": []}?”
Technical details
Endpoint
POSThttps://pennyrail.vercel.app/api/p/nano/json.keys--list-json-keysWhen to prefer
Choose this endpoint when you need a quick, paid, machine-readable enumeration of top-level JSON keys without setting up any local parsing logic. It is useful in agent pipelines where the JSON structure of a dynamic or unknown payload needs to be discovered programmatically before downstream processing. Prefer it over custom code when operating in a tool-calling context where invoking a microservice is more convenient than running code.
Side effects
- Missing or malformed 'input' field returns an error — input must be a JSON object, not a scalar or array
- Empty object input returns an empty key list rather than an error
- Non-object values nested inside the input are not recursively enumerated — only top-level keys are returned
- Payment failure (402) if USDC balance or x402 authorization is insufficient
- Vercel cold-start latency may cause occasional slow responses on first call
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Output
Schema · Response
{
"type": "object",
"additionalProperties": true
}Tags
x402
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