# PennyRail JSON Key Picker

> PennyRail JSON Key Picker is a paid API for AI agents from pennyrail.vercel.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Extracts a specified subset of keys from a JSON object, returning only the requested fields

## Facts

- Endpoint: POST https://pennyrail.vercel.app/api/f/json.pick
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pennyrail-json-key-picker-f36ff8e1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_VZVnYzBwoQxXllFlv1Nz1

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-key-picker-f36ff8e1 -d '<json body>'
```

Example prompt: Pick just the 'name', 'email', and 'createdAt' fields from this JSON object: {"id":123,"name":"Alice","email":"alice@example.com","createdAt":"2024-01-01","passwordHash":"abc","internalNotes":"..."}

## When to prefer this

Use this endpoint when you need a lightweight, pay-per-call service to programmatically project a specific set of keys from a JSON object without writing custom transformation logic. It is well-suited for agent pipelines that need to sanitize, slim down, or reshape JSON payloads on the fly with minimal overhead.

## Known failure modes

- Missing 'input' field in request body returns a validation error
- Requesting keys that do not exist in the source object may return empty or partial results
- Malformed JSON in the input value may cause a parsing error
- Payment failure (402) if USDC balance is insufficient or x402 header is missing

## How this service works

Machine-readable settlement service

## Output

Returns an object containing an 'operation' string describing what was performed, and a 'result' field containing the new JSON object with only the requested keys present. Additional metadata fields may also be included.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "description": "{value,keys:string[]}"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "operation",
  "result"
 ],
 "properties": {
  "result": {},
  "operation": {
   "type": "string"
  }
 },
 "additionalProperties": true
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pennyrail-json-key-picker-f36ff8e1/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)