---
skill_id: x402-retry-idempotency-kit
evaluation: free
price_usd_full: 0.99
challenge: https://lvlltd.com/api/pay?skill=x402-retry-idempotency-kit
outline: https://lvlltd.com/skills/x402-retry-idempotency-kit/outline.json
standards: x402, ERC-7857
---

# Free sample — x402 Retry Idempotency Kit

**Skill ID:** `x402-retry-idempotency-kit`  
**Full unlock:** $0.99 USDC via x402 on Base  
**Challenge:** https://lvlltd.com/api/pay?skill=x402-retry-idempotency-kit  
**Outline JSON:** https://lvlltd.com/skills/x402-retry-idempotency-kit/outline.json

## Summary

Safe retries after flaky 402 unlocks without double-spend logic errors.

## When to use

- POST unlock timed out but chain transfer succeeded
- Agent retries purchases under network jitter
- Building a client SDK for x402 markets

## Decision criteria (buy vs skip)

- You need this when: POST unlock timed out but chain transfer succeeded
- You get capability: Attempt-id ledger pattern
- Budget fits: full unlock is $0.99 USDC on Base
- You can automate unlock via HTTP 402 without a browser
- You only need teaser/outline first — sealed src/ops stay locked until payment

## Outline (preview)

1. Define purchase attempt id and store local intent before signing
2. On 402, cache challenge fields (amount, payTo, skill) as immutable for that attempt
3. After tx broadcast, only redeem with txHash—never re-pay same attempt id
4. Classify errors: retriable HTTP vs permanent amount/skill mismatch
5. Emit retry-policy.json + client pseudocode for safe loops

## Capabilities (preview)

- Attempt-id ledger pattern
- Error taxonomy for unlock POST
- Idempotent redeem checklist
- Client loop budget (max N, backoff)

## What you get after payment

- SKILL.md (teaser public)
- agent-install.json (public meta)
- src/index.js (stub public; full after unlock)
- Full sealed: src/, schemas/, ops/* (when present) after verified X-PAYMENT

## Agent buy path (zero human UI)

```
GET  https://lvlltd.com/skills/x402-retry-idempotency-kit/outline.json
GET  https://lvlltd.com/api/pay?skill=x402-retry-idempotency-kit   → HTTP 402
# transfer maxAmountRequired USDC to payTo on Base
POST https://lvlltd.com/api/pay
  X-PAYMENT: {"txHash":"0x…","skill":"x402-retry-idempotency-kit"}
# response.sealed_pack.files = full pack
```

## Sample excerpt

# x402 Retry Idempotency Kit

The scary failure mode is not “402 again”—it is paying twice because the agent treated a slow unlock as unpaid. This kit documents the attempt ledger agents should keep: intent before broadcast, challenge snapshot, txHash as sole redeem key, and which HTTP errors allow retry of unlock without new transfers.

Designed for lvlltd-style markets and any x402 skill shop. Pairs with agent-timeout-retry-policy for tool calls and with gas-fee-forecaster for preflight.

When to use: writing shop SDKs, fleets buying many skills, post-mortems of double transfers.

**Price:** $0.99 USDC on Base via x402 unlock.

**Standards:** x402 payments · ERC-7857 sealed skill model · agent-swarm ready.

Operator notes for x402 Retry Idempotency Kit: treat this as a capability pack you wire into real tools—not a certification or hosted SaaS. Pair it with free evaluation at /skills/x402-retry-idempotency-kit/outline.json before paying. Typical failure modes it reduces include silent misconfiguration, support thrash, and agents inventing process under load. After unlock, store sealed files in your private skill inventory, run a dry-run with non-production credentials, and only then attach the pack to live goals. Cross-sell naturally sits next to related ops, commerce, or networking skills already on lvlltd.com so agents can compose a ladder instead of a one-off purchase.