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.
npx skills add helmedeiros/clean-code-skills --skill solid-liskov-substitutiongit clone --depth 1 https://github.com/helmedeiros/clean-code-skillsWrote 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.
[](https://agentmods.dev/skills/helmedeiros/clean-code-skills/solid-liskov-substitution)<a href="https://agentmods.dev/skills/helmedeiros/clean-code-skills/solid-liskov-substitution"><img src="https://agentmods.dev/badge/skills/helmedeiros/clean-code-skills/solid-liskov-substitution/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.
<a href="https://agentmods.dev/skills/helmedeiros/clean-code-skills/solid-liskov-substitution"><img src="https://agentmods.dev/badge/skills/helmedeiros/clean-code-skills/solid-liskov-substitution.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00054 | $0.00748 |
| Opus 5 | $0.00027 | $0.00374 |
| Sonnet 5 | $0.00011 | $0.00150 |
| Haiku 4.5 | $0.00005 | $0.00075 |
Grade A, and why
solid-liskov-substitution 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 8d 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.
How it starts
The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SOLID: Liskov Substitution Principle
Verify that subtypes can replace their base types without altering the correctness of the program — every subclass must honor the contract of its parent.
When This Skill Applies
- Designing or reviewing inheritance hierarchies
- A subclass overrides a method in a way that changes expected behavior
- Runtime errors or bugs appear when substituting a derived type
- The user mentions LSP, Liskov substitution, or behavioral subtyping
- Code uses
instanceofchecks to handle different subtypes differently
Core Principle
If S is a subtype of T, then objects of type T can be replaced with objects of type S without altering any of the desirable properties of the program. Subtypes must honor the base type's contract: same preconditions (or weaker), same postconditions (or stronger), and preserved invariants. Violations create fragile hierarchies where polymorphism becomes unreliable.
Workflow
Step 1: Define the Base Contract
Document the base type's contract: what preconditions callers must satisfy, what postconditions the method guarantees, and what invariants the class maintains.
Step 2: Check Each Subtype
For every overriding method in each subtype, verify:
- Preconditions are not strengthened (subtype must accept everything the base accepts)
- Postconditions are not weakened (subtype must guarantee at least what the base guarantees)
- Invariants are preserved (subtype does not break class-level rules)
Step 3: Test Substitutability
Write tests using the base type reference. Run them with every subtype. All must pass without modification.
Step 4: Fix Violations
If a subtype cannot honor the base contract, it should not extend that base. Use composition instead, or redesign the hierarchy.
Detection / Indicators
- A subclass throws an exception where the base class does not
- A subclass ignores or no-ops a base class method
- Code checks
instanceofbefore calling a method - A subclass has stricter input validation than its parent
- Overridden methods return different types or null where the parent returns a value
- The "is-a" relationship feels forced: "is a Square a Rectangle?"
What ships with it
1 file 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.
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.
- 8d ago First seen · 73 lines · 54 tokens per session scan A f57eaa70d730
solid-liskov-substitution is a skill published in the GitHub repository helmedeiros/clean-code-skills (2 stars, last pushed 6mo ago), licensed MIT. It adds 54 tokens to every session and 748 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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