property-based-testing

A guide to property-based testing for serialization, validation, normalization, and pure functions. Property-based testing checks general rules across many generated inputs instead of only fixed examples.

In plain words
What is it for?
Use it when testing data conversion, input validation, data normalization, or functions without side effects.
Why use it?
It helps find edge cases that example-based tests may miss.

Skill for Claude CodeCodex

Part of the house-style plugin — 9 skills shipped together

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/pbdeuchler/llm-plugins/property-based-testing
Any agent
npx skills add pbdeuchler/llm-plugins --skill property-based-testing
Clone the repo
git clone --depth 1 https://github.com/pbdeuchler/llm-plugins

Made for: Claude Code, Codex.

Or install house-style, the plugin that ships this one along with the rest of its 9 skills.

Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,311 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00033 $0.01311
Opus 5 $0.00016 $0.00656
Sonnet 5 $0.00007 $0.00262
Haiku 4.5 $0.00003 $0.00131

Measured 3d ago against content hash 99c3957eb3a8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

property-based-testing 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.

plugins/house-style/skills/property-based-testing/SKILL.md · 153 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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 · 153 lines · 33 tokens per session scan A 99c3957eb3a8

Subscribe to this mod's changes

property-based-testing is a skill published in the GitHub repository pbdeuchler/llm-plugins (13 stars, last pushed 2mo ago), with no licence file. It adds 33 tokens to every session and 1,311 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.