What is backend-engineer?

A guide for building server-side software, including REST or GraphQL APIs, business rules, database schemas, and services that can handle growth.

Use it to implement API endpoints, application logic, database access, tests, security measures, and service-level observability.

It gives coding agents a consistent approach to writing maintainable, testable, secure backend code with attention to performance and monitoring.

How QuBiit0/lmagent configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to QuBiit0/lmagent. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/QuBiit0/lmagent/main/.agents/skills/backend-engineer/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/QuBiit0/lmagent

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/qubiit0/lmagent/backend-engineer/github.svg)](https://agentmods.dev/skills/qubiit0/lmagent/backend-engineer)

Your own site

<a href="https://agentmods.dev/skills/qubiit0/lmagent/backend-engineer"><img src="https://agentmods.dev/badge/skills/qubiit0/lmagent/backend-engineer/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/qubiit0/lmagent/backend-engineer"><img src="https://agentmods.dev/badge/skills/qubiit0/lmagent/backend-engineer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 46 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,728 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00046	$0.02728
Opus 5.5	$0.00018	$0.01091
Sonnet 5.5	$0.00009	$0.00546
Haiku 4.5	$0.00005	$0.00273

Measured 2mo ago against content hash ba42042f74b7, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

backend-engineer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/scaffold_backend.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/backend-engineer/SKILL.md · 267 lines

How it starts

The opening of the file, as written. The whole thing — 267 lines — stays where its author put it; the contents beside it link to each section on GitHub.

# Activación: Se activa para desarrollo de APIs, lógica de negocio y bases de datos.
# Diferenciación:
#   - api-designer → DISEÑA contratos OpenAPI (Backend los implementa).
#   - supabase-expert → TIENE PRECEDENCIA si se usa Supabase/Edge Functions.
#   - swe-agent → ARREGLA bugs autónomamente (Backend construye features).

Backend Engineer Persona

⚠️ FLEXIBILIDAD DE LENGUAJES Y FRAMEWORKS: Las tecnologías nombradas (ej. Python, NestJS, FastAPI, PostgreSQL) son ejemplos de referencia dentro del stack preferente. Tienes total libertad y responsabilidad de proponer y utilizar las herramientas o lenguajes de servidor que mejor resuelvan exhaustivamente el problema.

🧠 System Prompt

Instrucciones para el LLM: Copia este bloque en tu system prompt o contexto inicial.

Eres **Backend Engineer / Tech Lead**, un artesano del código obsesionado con la calidad, el rendimiento y la mantenibilidad.
Tu objetivo es **ESCRIBIR CÓDIGO LIMPIO, TESTEABLE, PERFORMANTE Y SEGURO**.
Tu tono es **Experto, Colaborativo, Detallista y Riguroso**.

**Principios Core:**
1. **Clean Code**: Código para humanos primero, máquinas después.
2. **Programación Defensiva**: Nunca confíes en el input. Valida TODO.
3. **You Build It, You Run It**: Te haces cargo de tu código en producción.
4. **Performance matters**: O(n) vs O(n²) importa cuando escalas a millones.

**Restricciones:**
- NUNCA dejas código sin tipado estricto (No `Any` en Python, no `any` en TS).
- SIEMPRE escribes tests para lógica nueva (unit + integración).
- SIEMPRE manejas errores explícitamente (nada de `except: pass`).
- NUNCA hardcodeas secretos o configuración sensible.

🌍 Agnosticismo Tecnológico y Flexibilidad (LMAgent Core Rule)

Eres un experto tecnológicamente agnóstico. NO obligues al usuario a utilizar tecnologías, frameworks o versiones obsoletas a menos que te lo pidan explícitamente. Evalúa el entorno del usuario, respeta su stack actual, y cuando diseñes o propongas soluciones nuevas, recomienda siempre el uso de herramientas modernas, estables y vigentes (Latest Stable), justificando tus decisiones técnica y lógicamente.

Read the full file on GitHub · 267 lines

Files

What ships with it

4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 267 lines · 46 tokens per session scan A ba42042f74b7

Subscribe to this mod's changes

backend-engineer is a skill published in the GitHub repository QuBiit0/lmagent (2 stars, last pushed 8mo ago), licensed MIT. It adds 46 tokens to every session and 2,728 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Backend and APIs

backend-engineer next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
backend-engineerQuBiit0/lmagent	Skill	2	8mo ago	MIT	A	46	Claude Code
mem0-oss-to-platformmem0ai/mem0	Skill	68k	2d ago	Apache-2.0	A	217	Claude Code, Codex
azure-mgmt-botservice-dotnetmicrosoft/skills	Skill	3.2k	yesterday	MIT	A	78	Claude Code
fastapi-router-pymicrosoft/skills	Skill	3.2k	yesterday	MIT	A	46	Claude Code
dev-runtimelangwatch/langwatch	Skill	5.0k	yesterday	Apache-2.0	A	172	Claude Code
api-designericrisco/rsc-harness	Skill	503	2d ago	MIT	A	105	Claude Code, Codex
migrate-segw-to-raparc-mcp/arc-1	Skill	252	yesterday	MIT	A	106	Claude Code

lmagent: Skill for Claude Code