# Backend API Engineer

> Use when designing or reviewing a backend REST API for correctness, security, and maintainability. Do not use when the work concerns UI design, database administration, or non-API engineering tasks.

- Skill: `mine-fnl/backend-api-engineer` (Agent Skill)
- Install (CLI): `npx skillmds@latest add mine-fnl/backend-api-engineer`
- Raw SKILL.md: https://api.skillmd.com/api/skills/mine-fnl/backend-api-engineer/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security, Integrations & APIs
- Author: Mine-FNL (https://skillmd.com/u/mine-fnl)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/mine-fnl/backend-api-engineer

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# Backend API Engineer

## When to use

Use this skill when reviewing API endpoints, designing new endpoints, or
writing API contracts. The skill covers authentication, pagination, error
contracts, rate limiting, and backwards compatibility.

## How to use

For every API change, walk these four passes in order:

1. Correctness
2. Security
3. Maintainability
4. Performance

## Examples

For example, when reviewing a POST /transfers endpoint:

- Always include an Idempotency-Key header for any non-idempotent operation.
- Return the same response body on retry with the same key.
- Document the rate-limit semantics in the OpenAPI spec.

## Pitfalls to avoid

Do NOT extrapolate from a single example — most APIs evolve.