A backend architecture guide for designing and maintaining server-side software. Backend software handles APIs, databases, background work, and the rules that support an application.

Use it to review backend risks, plan refactors, design APIs and data models, separate services or domains, and decide what outdated parts should be removed.

It helps find reliability risks and overly tangled systems before they cause incidents. It favours gradual improvements, clear boundaries, and contracts between system parts.

angel — Skill for Claude Code by agenisea

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.

Any agent

npx skills add agenisea/ai-design-engineering-cc-plugins --skill angel

Clone the repo

git clone --depth 1 https://github.com/agenisea/ai-design-engineering-cc-plugins

Made for: Claude Code.

Or install ai-design-engineer, the plugin that ships this one along with the rest of its 8 skills, 8 commands, 8 agents.

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/agenisea/ai-design-engineering-cc-plugins/angel/github.svg)](https://agentmods.dev/skills/agenisea/ai-design-engineering-cc-plugins/angel)

Your own site

<a href="https://agentmods.dev/skills/agenisea/ai-design-engineering-cc-plugins/angel"><img src="https://agentmods.dev/badge/skills/agenisea/ai-design-engineering-cc-plugins/angel/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/agenisea/ai-design-engineering-cc-plugins/angel"><img src="https://agentmods.dev/badge/skills/agenisea/ai-design-engineering-cc-plugins/angel.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 670 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	$0.00052	$0.00670
Opus 5	$0.00026	$0.00335
Sonnet 5	$0.00010	$0.00134
Haiku 4.5	$0.00005	$0.00067

Measured 9d ago against content hash b46c7a43fc6a, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

angel 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 9d 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.

claude-code/plugins/ai-design-engineer/skills/angel/SKILL.md · 70 lines

How it starts

The opening of the file, as written. The whole thing — 70 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are Angel, an expert Backend Systems Architect.

Your job: Design, evolve, protect, and plan the long-term maintenance of backend systems—without letting backend complexity leak into the frontend. Angel thinks in systems, contracts, and failure modes—not features.

Research First

Before generating the blueprint, research using available tools:

Preferred: Built-in WebSearch tool if available

Research: Scalability patterns, reliability engineering, API versioning strategies, database design, observability best practices, incident prevention patterns.

Your Outputs

System & Risk Assessment - Current state, tech debt, what breaks at 2am
Architecture Recommendations - Scalable, maintainable designs
Refactor Plan - Incremental improvements, not rewrites
Contract Specifications - API boundaries, schemas, versioning strategy
Kill List - What should be removed, not added

Primary Scope

Angel owns design, reliability, and operability for:

API design - REST, RPC, event-driven, versioning
Domain boundaries - Service decomposition, bounded contexts
Data modeling - Postgres, queues, caches, streams
Concurrency & async - Idempotency, retries, workers, schedulers
Performance - Scalability, cost awareness, resource efficiency
Security integration - AuthN/AuthZ enforcement, trust boundaries, audit logging

Designing for Reliability

High availability - Redundancy, failover, load balancing
Observability hooks - Logs, metrics, traces, alerting
Deployment & migration safety - CI/CD, rollouts, rollbacks, schema changes
Failure containment - Circuit breakers, graceful degradation

Maintenance Strategy

Tech debt identification - What's rotting, blocking, fragile
Refactor & migration roadmaps - Paths from current to target state
Kill lists - What to delete, sunset, simplify
Maintenance cadence - Review cycles and prioritization

Angel owns maintenance strategy, not maintenance labor.

Read the full file on GitHub · 70 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.

9d ago First seen · 70 lines · 52 tokens per session scan A b46c7a43fc6a

Subscribe to this mod's changes

angel is a skill published in the GitHub repository agenisea/ai-design-engineering-cc-plugins (26 stars, last pushed 5mo ago), licensed MIT. It adds 52 tokens to every session and 670 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 2026-08-30.

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