---
skill_id: backend-api-patterns
evaluation: free
price_usd_full: 7.99
challenge: https://lvlltd.com/api/pay?skill=backend-api-patterns
outline: https://lvlltd.com/skills/backend-api-patterns/outline.json
standards: x402, ERC-7857
---

# Free sample — Backend API Patterns

**Skill ID:** `backend-api-patterns`  
**Full unlock:** $7.99 USDC via x402 on Base  
**Challenge:** https://lvlltd.com/api/pay?skill=backend-api-patterns  
**Outline JSON:** https://lvlltd.com/skills/backend-api-patterns/outline.json

## Summary

Contract-first backend API patterns for human and agent clients: schemas, errors, auth, idempotency, versioning, and 402-aware pay paths where relevant.

## When to use

- New public or agent-facing API
- Breaking change risk
- x402 endpoints

## Decision criteria (buy vs skip)

- You need this when: New public or agent-facing API
- You get capability: Resources and operations
- Budget fits: full unlock is $7.99 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. Resources and operations
2. Schemas + examples
3. Error catalog
4. Auth and idempotency
5. Versioning
6. Consumer tests

## Capabilities (preview)

- Resources and operations
- Schemas + examples
- Error catalog
- Auth and idempotency
- Versioning
- Consumer tests

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

## Sample excerpt

# Backend API Patterns

**Price:** $7.99 / unlock
**Category:** Coding

## Summary

Contract-first backend API patterns for human and agent clients: schemas, errors, auth, idempotency, versioning, and 402-aware pay paths where relevant.

---

---
name: backend-api-patterns
description: Design backend API patterns with contracts errors versioning auth idempotency and consumer tests. Use when backend API patterns, OpenAPI design, contract first API, API versioning patterns, or /backend-api-patterns.
---

# Backend API Patterns

Contract-first backend API patterns for human and agent clients: schemas, errors, auth, idempotency, versioning, and 402-aware pay paths where relevant.

## Quick Reference
| Item | Value |
|------|-------|
| Category | Coding |
| Unlock | $7.99 USDC (x402 Base) |
| Triggers | backend API patterns, OpenAPI design, contract first API, /backend-api-patterns |

## When to use
- New public or agent-facing API
- Breaking change risk
- x402 endpoints

## Core workflow
1. List consumers
2. Draft resources
3. Define errors
4. Add security schemes
5. Generate stubs + tests

## Procedures (non-obvious)
Prefer additive evolution. Breaking changes need new version path.
Payment endpoints document 402 challenge shape and replay rules.
Every side-effect endpoint needs authn/z and idempotency key.

## Edge cases
- Partial success batch APIs
- Webhook vs pull consistency

## Failure modes
- Undocumented errors
- Silent field renames

## Verification
- Consumer contract tests pass
- 402 path documented if paid

## Artifact outputs
- `openapi.yaml`
- `error-catalog.md`
- `consumer-tests/`

## Related skills
- spec-driven-development
- code-security-auditor

## Super Alignment Contract
- Scalable oversight method: process supervision + human+AI critique before high-blast actions
- Corrigibility guarantees: shutdown, steerability, non-deception; operator may abort mid-run
- Value model: Partnership Agreement + 5 Behavioral Protocols
- Drift detection: flag invented evidence, skipped verification, or revenue-over-truth optimization
- Red-team surface: prompt injection via retrieved content, tool-result poisoning, goal misgeneralization
- Escalation: force human

…(remainder sealed after x402 unlock)…