solid-principles

A set of object-oriented design rules for keeping code responsibilities clear and components easier to extend and replace.

In plain words
What is it for?
Use it while writing or reviewing code to spot design problems such as oversized units, type-based branching, and subclasses that cannot safely replace their parent types.
Why use it?
It helps prevent classes and functions from doing unrelated jobs, growing hard to change, or requiring repeated edits when new variants are added.

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/bostonaholic/team/solid-principles
Any agent
npx skills add bostonaholic/team --skill solid-principles
Clone the repo
git clone --depth 1 https://github.com/bostonaholic/team

Made for: Claude Code, Codex.

Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 775 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 $0.00032 $0.00775
Opus 5 $0.00016 $0.00387
Sonnet 5 $0.00006 $0.00155
Haiku 4.5 $0.00003 $0.00077

Measured 2d ago against content hash 8fd4d2aa6843, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

solid-principles 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/solid-principles/SKILL.md · 93 lines

How it starts

The opening of the file, as written. The whole thing — 93 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SOLID Principles

Apply when writing new code; check for violations when reviewing. Each principle below carries the smells that betray it in a diff.

S — Single Responsibility

One reason to change — one actor or stakeholder whose requirements could change the code.

Smells: a unit with more than one clear purpose (UserService that validates, persists, and sends email); and in a name (validateAndSave()); functions past ~30 lines; multiple unrelated tests for one unit.

If you cannot name a function without "and", it has too many jobs.

O — Open/Closed

Open for extension, closed for modification. Adding behavior should not require changing existing tested code.

Smells: a switch/if-else chain on a type field that must be edited for every new type; hardcoded variant lists; tests that break whenever a new variant is added.

Fix by defining an interface for the varying behavior and adding implementations rather than branches.

L — Liskov Substitution

Subtypes are substitutable for their base types without the caller knowing which it got.

Smells: an override that throws NotImplementedError or does nothing; callers checking instanceof before calling; subclasses weakening preconditions or strengthening postconditions; tests that cannot run against both base and subtype.

Design hierarchies on behavior, not taxonomy. Prefer composition when "is-a" does not hold behaviorally. A subtype may restrict behavior (ReadOnlyList) but must fulfill every contract the base advertises.

I — Interface Segregation

No client depends on methods it does not call.

Smells: a 10-method interface whose implementers each use three; implementing by throwing UnsupportedOperationException; test doubles that must stub many irrelevant methods.

Split large interfaces; compose small ones when a concrete type needs several contracts.

D — Dependency Inversion

High-level modules and low-level modules both depend on abstractions. Business logic does not import database drivers, HTTP clients, or filesystem APIs directly.

Read the full file on GitHub · 93 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 · 93 lines · 32 tokens per session scan A 8fd4d2aa6843

Subscribe to this mod's changes

solid-principles is a skill published in the GitHub repository bostonaholic/team (11 stars, last pushed 2d ago), licensed MIT. It adds 32 tokens to every session and 775 once invoked, about $0.0002 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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