solid

A set of five software-design principles known as SOLID, used to organize modules, interfaces, and classes. The principles aim to keep responsibilities clear and make systems easier to change and test.

In plain words
What is it for?
Use it when structuring modules or class hierarchies, designing interfaces, reducing coupling, or making code easier to test and maintain.
Why use it?
It helps prevent changes in one part of a codebase from causing unrelated parts to break. It also guides decisions about dependency injection, interfaces, and module boundaries.

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/jordancoin/codingskills/solid
Any agent
npx skills add JordanCoin/codingskills --skill solid
Clone the repo
git clone --depth 1 https://github.com/JordanCoin/codingskills

Made for: Claude Code, Codex.

Per session 65 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,426 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 $0.00065 $0.01426
Opus 5 $0.00032 $0.00713
Sonnet 5 $0.00013 $0.00285
Haiku 4.5 $0.00006 $0.00143

Measured 3d ago against content hash 75d5bce7809a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

solid 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 3d 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/solid/SKILL.md · 134 lines

How it starts

The opening of the file, as written. The whole thing — 134 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SOLID Principles

Before Applying

If .agents/stack-context.md exists, read it first. Apply this principle using idiomatic patterns for the detected stack. For framework-specific details, use context7 MCP or web search — don't guess.

Principle

Five design principles that produce modular, testable, and resilient systems. While originally framed for object-oriented design, the underlying ideas apply to any paradigm — functions, modules, services, or components.

Why This Matters in Production

SOLID code is change-friendly code. Production systems change constantly — new features, bug fixes, integrations, scaling. Systems designed with SOLID principles absorb change locally rather than requiring cascading modifications. This means fewer regressions, faster feature delivery, and smaller blast radius when things go wrong.


S — Single Responsibility Principle

A module should have one, and only one, reason to change.

Every module, function, or component should own exactly one piece of functionality. When a change request comes in, you should be able to predict which file needs editing without searching.

Violations look like:

  • A function that validates input, queries the database, applies business logic, and formats the response
  • A "utils" file that grows indefinitely because nothing else has a clear home
  • A class that changes every time any feature in the system changes

Apply it:

  • If a function does two things, split it into two functions
  • If a module handles both "what to do" and "how to do it," separate policy from mechanism
  • Name modules after their responsibility — if the name is vague ("Manager", "Helper", "Utils"), the responsibility is unclear

O — Open/Closed Principle

Software should be open for extension but closed for modification.

You should be able to add new behavior without modifying existing, working code. This doesn't mean you never touch existing code — it means you design so that the common extension points don't require it.

Read the full file on GitHub · 134 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. 3d ago First seen · 134 lines · 65 tokens per session scan A 75d5bce7809a

Subscribe to this mod's changes

solid is a skill published in the GitHub repository JordanCoin/codingskills (7 stars, last pushed 6mo ago), licensed MIT. It adds 65 tokens to every session and 1,426 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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