# PennyRail Number Sum

> PennyRail Number Sum 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).

Computes the sum of an array of numbers via a paid REST API endpoint

## Facts

- Endpoint: POST https://pennyrail.vercel.app/api/f/number.sum
- 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-number-sum-30b8b8af
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_ZDrN4qrfrYBQhwpoTw4Un

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-number-sum-30b8b8af -d '<json body>'
```

Example prompt: Can you add up these numbers for me using PennyRail: 14, 27, 3, 99, and 5?

## When to prefer this

Choose this endpoint when you need a simple, machine-readable summation of a list of numbers over a paid x402-compatible API, especially in agentic workflows that already handle micropayment authorization via the x402 protocol. Best suited for lightweight numeric aggregation tasks where spinning up a compute environment is overkill.

## Known failure modes

- Missing 'input' field returns validation error
- Empty array may return 0 or an error depending on implementation
- Non-numeric values in the array may cause computation failure or be ignored
- Payment not processed (402 response) if USDC balance is insufficient
- Network timeout on the Vercel deployment under cold-start conditions

## How this service works

Machine-readable settlement service

## Output

Returns a JSON object with an 'operation' string (e.g. 'sum') and a 'result' field containing the computed sum of the input numbers.

## Request schema (JSON Schema)

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

## 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-number-sum-30b8b8af/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)