# PennyRail JSON Keys & Fields Extractor

> PennyRail JSON Keys & Fields Extractor 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 the keys and fields present in a submitted JSON object, enabling machine-readable inspection of JSON structure

## Facts

- Endpoint: POST https://pennyrail.vercel.app/api/p/nano/json.keys--json-fields
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pennyrail-json-keys-fields-extractor-8ea21d73
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_vM99l8dmzQ1T123Z9_aKk

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability pennyrail-json-keys-fields-extractor-8ea21d73 -d '<json body>'
```

Example prompt: Can you pull out all the keys and field names from this JSON object for me? Here it is: {"user": {"id": 42, "name": "Alice", "roles": ["admin", "editor"]}, "created_at": "2024-01-01"}

## When to prefer this

Choose this endpoint when you need a lightweight, pay-per-call microservice to enumerate the keys or fields of a JSON object without setting up local parsing logic, or when operating in an agent pipeline that uses x402 micropayment-gated APIs. It is best suited for dynamic schema discovery, payload inspection, and cases where the JSON structure is unknown or variable.

## Known failure modes

- Input object is missing or malformed — returns a 400-level error
- Input is not a valid JSON object — schema validation failure
- Payment not settled via x402 protocol — returns 402 Payment Required
- Empty object submitted — may return an empty keys list
- Deeply nested structures may only return top-level keys depending on implementation

## How this service works

Machine-readable settlement service

## Output

A JSON object containing the enumerated keys and field names found within the submitted input object, allowing the caller to inspect the structure and properties of the original JSON without needing to parse it manually.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "additionalProperties": true
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pennyrail-json-keys-fields-extractor-8ea21d73/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from pennyrail.vercel.app](https://www.zero.xyz/host/pennyrail.vercel.app/llms.txt)