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 agentmods add skills/melodic-software/claude-code-plugins/principlesnpx skills add melodic-software/claude-code-plugins --skill principlesgit clone --depth 1 https://github.com/melodic-software/claude-code-pluginsWrote 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/melodic-software/claude-code-plugins/principles)<a href="https://agentmods.dev/skills/melodic-software/claude-code-plugins/principles"><img src="https://agentmods.dev/badge/skills/melodic-software/claude-code-plugins/principles.svg" alt="Measured on agentmods" 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 | $0.00159 | $0.01215 |
| Opus 5 | $0.00079 | $0.00607 |
| Sonnet 5 | $0.00032 | $0.00243 |
| Haiku 4.5 | $0.00016 | $0.00121 |
Grade A, and why
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 yesterday.
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 — 78 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mutation Testing Knowledge Base
Distilled from the primary sources, the foundational papers, the industrial-scale reports, and the
tool documentation that defines the vocabulary everyone else borrows. Reference files in
reference/ are source-attributed; this file routes and answers the common questions without a load.
Routing Table
| Query about... | Load |
|---|---|
| Mutant states (killed/survived/no-coverage/timeout), operator catalogs, what a mutation actually is | operators-and-states.md |
| Mutation score, covered-code score, test strength, MSI, the oracle gap, what to report | metrics.md |
| Cost, diff-scoping, arid nodes, productive vs unproductive mutants, suppression, why not to gate | scaling-and-suppression.md |
| Which tool for which ecosystem, what each supports, what to do when no tool exists | tooling.md |
| Equivalent mutants, coupling effect, competent programmer hypothesis, the theory | theory.md |
Quick decision guide (no load required)
"What is mutation testing?". Coverage tells you a line executed. It cannot tell you the line was checked. Mutation testing introduces a small deliberate fault (a mutant), re-runs the tests, and observes: tests fail → the mutant is killed, something genuinely asserted on that behavior; tests pass → the mutant survived, that line ran and nothing noticed it was wrong. The mutation is always reverted; the source is unchanged at the end.
"Is it just better coverage?". It answers a different question. Coverage measures execution; mutation testing measures fault detection. PIT states it directly: line coverage "does not check that your tests are actually able to detect faults." A file at 100% coverage and 40% mutation score has tests that run the code and assert almost nothing about it.
"Which number do I look at?". The covered-code one, always. Plain mutation score mixes two unrelated problems: "my tests are weak" and "I have no tests here." The covered-code variant (PIT calls it test strength, Infection calls it Covered Code MSI) isolates the first. A wide gap between the two means the coverage you have is thin, not that the tests are bad.
What ships with it
6 files 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.
- yesterday First seen · 78 lines · 159 tokens per session scan A e4e2a7d1b6e3
principles is a skill published in the GitHub repository melodic-software/claude-code-plugins (15 stars, last pushed today), licensed MIT. It adds 159 tokens to every session and 1,215 once invoked, about $0.0008 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 2026-09-03.
Other skills, from other repositories
count-combinations
For probability and counting: permutations, combinations, sample spaces, Monte Carlo simulation, brute-force enumeration, card/dice problems.
solve-constraint-puzzle
For constraint satisfaction: Sudoku, scheduling, N-queens, logic puzzles, SAT-like problems, assignment problems. Uses propagate-then-search pattern.
career-path-planner
Career goal mapping with skill gap analysis, actionable development plans, and milestone tracking. Use when planning career transitions, identifying skill gaps, setting professional development goals, or evaluating career options.
case-interview-practice
Interactive consulting case interview practice with structured frameworks, feedback mechanisms, and progressive difficulty. Use when preparing for management consulting interviews, case competitions, or business problem-solving exercises.
course-material-creator
Create custom educational materials including syllabi, lesson plans, assessments, reading lists, and learning objectives. Use when building course curricula, training programs, workshops, or educational content.
testing
TDD/BDD testing principles. Use when writing tests, reviewing test coverage, setting up testing, or discussing test strategy and test architecture.