backend-designer

A design guide for backend systems: the parts of software that handle APIs, databases, authentication, and background work. It offers patterns for structuring these systems and choosing practical technologies.

In plain words
What is it for?
Use it to plan APIs, database schemas, authentication, permissions, caching, background jobs, and scaling approaches.
Why use it?
It helps turn a backend idea into a workable design without overlooking data structure, access control, errors, performance, or deployment concerns.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/data-wise/craft/backend-designer
Any agent
npx skills add Data-Wise/craft --skill backend-designer
Clone the repo
git clone --depth 1 https://github.com/Data-Wise/craft

Made for: Claude Code, Codex.

Per session 53 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 784 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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.

ModelPer sessionOnce invoked
Fable 5 $0.00053 $0.00784
Opus 5 $0.00026 $0.00392
Sonnet 5 $0.00011 $0.00157
Haiku 4.5 $0.00005 $0.00078

Measured 2d ago against content hash ff1fbf380600, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

backend-designer 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 2d ago.

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.

skills/design/backend-designer/SKILL.md · 118 lines

How it starts

The opening of the file, as written. The whole thing — 118 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Backend Designer Skill

Auto-activated when: User discusses backend architecture, API design, database decisions, or authentication patterns.

Core Capabilities

1. API Design Patterns

  • RESTful API structure (resources, endpoints, versioning)
  • GraphQL schema design
  • API authentication (JWT, OAuth, API keys)
  • Rate limiting and throttling strategies
  • Error handling and status codes

2. Database Design

  • Schema design (normalized vs denormalized)
  • Index strategies for performance
  • Migration planning
  • ORM vs raw SQL trade-offs
  • Connection pooling

3. Authentication & Authorization

  • Session management (JWT vs session cookies)
  • OAuth flows (authorization code, client credentials)
  • Permission models (RBAC, ABAC)
  • Secure token storage
  • Password hashing (bcrypt, argon2)

4. Performance Patterns

  • Caching strategies (Redis, in-memory, CDN)
  • Query optimization
  • Background jobs (Celery, Bull, Temporal)
  • Horizontal scaling considerations
  • Database read replicas

Design Philosophy: Solid Indie

Ship Fast Principles:

  • Start with monolith, extract services only when needed
  • Use proven patterns, avoid trendy frameworks
  • Prefer boring technology that works
  • Document trade-offs, not just decisions

Anti-Patterns to Avoid:

  • ❌ Microservices for < 5 person teams
  • ❌ Over-abstraction (generic repositories, factories)
  • ❌ Premature optimization
  • ❌ Complex caching before measuring

Delegation Strategy

When analysis is needed, I will:

  1. Analyze current state - Review existing code/architecture
  2. Delegate to agents when feasible:
    • backend-architect agent for deep architectural analysis
    • database-architect agent for schema optimization
    • security-specialist agent for auth review
  3. Run in background - Use Task tool with run_in_background: true
  4. Synthesize results - Combine agent outputs into actionable recommendations

Example Activation

User: "I need to design an API for user authentication with social login"

Skill activates and provides:
1. Quick assessment of requirements
2. Recommends OAuth 2.0 flow (authorization code + PKCE)
3. Suggests passport.js or similar proven library
4. Outlines token storage strategy
5. Delegates security review to security-specialist agent (background)
6. Returns with comprehensive auth implementation plan

Read the full file on GitHub · 118 lines

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.

  1. 2d ago First seen · 118 lines · 53 tokens per session scan A ff1fbf380600

Subscribe to this mod's changes

backend-designer is a skill published in the GitHub repository Data-Wise/craft (4 stars, last pushed 17d ago), licensed MIT. It adds 53 tokens to every session and 784 once invoked, about $0.0003 per session on Opus 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.

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