# PennyRail JSON Field Picker

> PennyRail JSON Field Picker is a paid API for AI agents from pennyrail.vercel.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-31).

Selects and returns a subset of fields from a JSON object, filtering out unwanted keys

## Facts

- Endpoint: POST https://pennyrail.vercel.app/api/p/nano/json.pick--pick-json-fields?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pennyrail-json-field-picker-8d44215b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_DVjcLkhk84ToZtqffS7G8

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-field-picker-8d44215b -d '<json body>'
```

Example prompt: Take this JSON object and give me back only the 'name', 'email', and 'createdAt' fields, dropping everything else.

## When to prefer this

Choose this endpoint when you need a lightweight, pay-per-call JSON field projection without standing up your own transformation logic. Best for agents that receive large, noisy JSON payloads and need to distill them to a smaller set of fields before passing data downstream.

## Known failure modes

- Missing or malformed 'input' field returns an error
- Requested field names not present in the input object may return empty or partial results
- Non-object input type may cause processing failure
- Payment failure (402) if USDC balance is insufficient

## How this service works

Machine-readable settlement service

## Output

A JSON object containing only the fields that were requested, with all other keys removed from the original input object.

## 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-field-picker-8d44215b/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)