A tool for property-based testing, a testing method that tries many automatically generated inputs and checks whether general rules always hold.

Use it to test Rust, Go, C++, TypeScript, Java, and OCaml functions, modules, or libraries for invariants, round trips, and other properties.

It finds unusual combinations and boundary cases that hand-written tests may miss, then reduces failures to smaller examples.

hegel — Skill for Claude Code by hegeldev

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.

Any agent

npx skills add hegeldev/hegel-skill --skill hegel

Clone the repo

git clone --depth 1 https://github.com/hegeldev/hegel-skill

Made for: Claude Code.

Or install hegel-skill, the plugin that ships this one along with the rest of its 1 skill.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/hegeldev/hegel-skill/hegel/github.svg)](https://agentmods.dev/skills/hegeldev/hegel-skill/hegel)

Your own site

<a href="https://agentmods.dev/skills/hegeldev/hegel-skill/hegel"><img src="https://agentmods.dev/badge/skills/hegeldev/hegel-skill/hegel/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/hegeldev/hegel-skill/hegel"><img src="https://agentmods.dev/badge/skills/hegeldev/hegel-skill/hegel.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 153 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 7,508 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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.

Model	Per session	Once invoked
Fable 5.1	$0.00153	$0.07508
Opus 5	$0.00077	$0.03754
Sonnet 5	$0.00031	$0.01502
Haiku 4.5	$0.00015	$0.00751

Measured 10d ago against content hash c898653c9495, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

hegel 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 10d 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/hegel/SKILL.md · 391 lines

How it starts

The opening of the file, as written. The whole thing — 391 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Hegel: Property-Based Testing

Hegel is a family of property-based testing libraries supporting multiple languages, powered by a shared native engine based on Hypothesis. Everything runs in-process, and tests integrate with standard language test runners. Hegel generates random inputs for your code and automatically shrinks failing cases to minimal counterexamples.

Even when PBTs add modest line coverage over unit tests, their value is in exercising combinations and boundary conditions that humans don't think to write by hand.

Code examples in this file use Python-like pseudocode to illustrate concepts. For exact API and syntax, load the language-specific reference (see step 1 of the workflow).

Workflow

Follow these steps when writing property-based tests.

Before touching a third-party project, check whether its maintainers have opted out of AI contributions. Look for an anti-AI clause in CONTRIBUTING.md/README/LICENSE, or a dedicated governance file gating AI work (some projects require an explicit acknowledgement step before AI-generated changes). If you find one, surface it to the user and stop — do not silently satisfy the acknowledgement requirement, bypass the gate, or upstream anything. Testing a local copy for your own understanding may still be fine, but the decision to proceed and especially to contribute back is the user's to make, not yours to assume.

1. Load the Language Reference

Determine the project language and load the corresponding reference from references/<language>/reference.md for API details and idiomatic patterns.

2. Explore the Code Under Test

Before writing any test, understand what you're testing:

Read the source code of the function/module under test
Read existing tests to understand expected behavior and edge cases
Read docstrings, comments, and type signatures for documented contracts
Read usage sites to see how callers use the code and what they expect

The goal is to find evidence for properties, not to invent them.

Read the full file on GitHub · 391 lines

Files

What ships with it

14 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.

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.

10d ago First seen · 391 lines · 153 tokens per session scan A c898653c9495

Subscribe to this mod's changes

hegel is a skill published in the GitHub repository hegeldev/hegel-skill (75 stars, last pushed 14d ago), licensed MIT. It adds 153 tokens to every session and 7,508 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 2026-08-30.

Testing

research-engineer

An uncompromising Academic Research Engineer. Operates with absolute scientific rigor, objective criticism, and zero flair. Focuses on theoretical correctness, formal verification, and optimal implementation across any required technology.

davila7/claude-code-templates · 43 tokens

tika-eval-compare

Compare extracts from two Tika builds over a corpus to detect regressions in content, encoding, exceptions, and embedded-document handling. Use for "compare before/after extracts", "eval this change against the corpus".

apache/tika · 50 tokens

neuron-evaluation-engineer

Create and run AI evaluations with datasets, assertions, and output drivers in Neuron AI. Use this skill whenever the user mentions evaluation, testing AI systems, creating evaluators, dataset-driven testing, assertion-based validation, or wants to measure AI system performance. Also trigger for tasks involving…

neuron-core/neuron-ai · 77 tokens

hegel