# Idempotency Replay Guard

> Idempotency Replay Guard is a paid API for AI agents from phion.systems, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).

Detects whether reuse of an idempotency key is a safe replay of a prior request or a conflicting misuse that should be rejected

## Facts

- Endpoint: POST https://phion.systems/v1/paid/trust/idempotency-replay-guard
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/idempotency-replay-guard-01f1945a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_O-_CrIGNZQl6AGtpX9r2L

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 idempotency-replay-guard-01f1945a -d '<json body>'
```

Example prompt: Before retrying this payment, check whether idempotency key 'pay-abc-1234' is a safe replay of a prior identical request or a conflicting reuse with different parameters.

## When to prefer this

Use this endpoint when an agent or system is about to retry an operation and needs to verify whether the idempotency key is being reused safely (identical request) or dangerously (different payload or intent). Especially valuable in x402 payment flows, multi-step agentic pipelines, or any workflow where duplicate execution has financial or state consequences. Prefer this over ad-hoc key comparisons when you need a structured, policy-driven verdict rather than a simple equality check.

## Known failure modes

- Insufficient key or payload context provided — returns validation error
- Key not found in prior request history — cannot determine replay vs. conflict
- Ambiguous payload diff — partial match may yield inconclusive classification
- Malformed idempotency key format — rejected at input validation
- Service unavailable or timeout — caller should not assume safe replay

## How this service works

Detect safe replays and conflicting reuse of an idempotency key

## Output

Returns a classification of the idempotency key reuse as either a safe replay (identical request repeated) or a conflicting reuse (same key, different parameters), along with relevant flags and evidence to guide the caller's decision on whether to proceed, reject, or escalate.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema"
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/idempotency-replay-guard-01f1945a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from phion.systems](https://www.zero.xyz/host/phion.systems/llms.txt)