# PennyRail JSON Key Filter (pick--keep-json-keys)

> PennyRail JSON Key Filter (pick--keep-json-keys) 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).

Filters a JSON object to retain only specified keys, returning a new object containing only the picked fields

## Facts

- Endpoint: POST https://pennyrail.vercel.app/api/p/nano/json.pick--keep-json-keys
- 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-key-filter-pick-keep-json-keys-4c58ef79
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_B-FOwX-J2Yedxb3P5Emmw

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-filter-pick-keep-json-keys-4c58ef79 -d '<json body>'
```

Example prompt: Take this JSON object and keep only the 'name', 'email', and 'created_at' fields — strip everything else out.

## When to prefer this

Use this endpoint when you need a lightweight, pay-per-call JSON key filtering operation without standing up your own transformation logic. Ideal for agent pipelines that need to slim down API responses or sanitize payloads before passing data to downstream steps. Prefer this over general-purpose code execution when you want a simple, stateless field-picker with minimal overhead.

## Known failure modes

- Missing 'input' field returns validation error
- If no matching keys exist in the object, returns an empty object
- Nested key paths may not be supported — only top-level keys may be filterable
- Payment failure (402) if USDC balance is insufficient
- Malformed JSON input may result in a 400 error

## How this service works

Machine-readable settlement service

## Output

A JSON object containing only the keys that were specified in the input filter list, with all other top-level properties removed. The structure of retained values is preserved as-is.

## 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-key-filter-pick-keep-json-keys-4c58ef79/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)