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 OutlineDriven/odin-claude-plugin --skill property-test-authoringgit clone --depth 1 https://github.com/OutlineDriven/odin-claude-pluginWrote 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/outlinedriven/odin-claude-plugin/property-test-authoring)<a href="https://agentmods.dev/skills/outlinedriven/odin-claude-plugin/property-test-authoring"><img src="https://agentmods.dev/badge/skills/outlinedriven/odin-claude-plugin/property-test-authoring/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/outlinedriven/odin-claude-plugin/property-test-authoring"><img src="https://agentmods.dev/badge/skills/outlinedriven/odin-claude-plugin/property-test-authoring.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00057 | $0.01765 |
| Opus 5 | $0.00028 | $0.00882 |
| Sonnet 5 | $0.00011 | $0.00353 |
| Haiku 4.5 | $0.00006 | $0.00177 |
Grade A, and why
property-test-authoring 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 6d 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 — 79 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Property test authoring
Contract
| Field | Bound contract |
|---|---|
| Trigger | The user asks to add or improve generated property tests for an inverse, invariant, oracle, idempotence rule, parser, normalizer, algorithm, data structure, or smart-contract state machine. |
| Authority | Reversible-local: write property tests to local files tracked by version control. Roll back with git revert or git checkout of the test file. |
| Side effect | Write property tests in the existing framework. Add a new testing dependency or production-code seam only with user approval. |
| Done | The strongest grounded property is encoded with domain-aware generators and pinned edge cases, avoids tautology and vacuity, and the targeted test run passes while a plausible contract violation would fail it. |
Inputs
- Target code: the function, module, or contract under test. Required.
- Property type: roundtrip, inverse, oracle, idempotence, invariant, commutativity, associativity, identity, or determinism. Inferred from the code's algebraic shape when not stated.
- Test framework: the project's existing property-based testing library (Hypothesis, fast-check, proptest, jqwik, rapid, Echidna, Medusa, or equivalent). Required.
- Existing tests: any current property or example tests for the target. Optional.
- Known edge cases: domain-specific boundary values. Optional.
Procedure
- Examine the target code for an algebraic shape. Check whether the shape is missing or merely buried. A calculation wrapped in I/O, a string built by concatenation, or an in-place mutation may have a property but no seam through which to assert it. If the shape is buried, identify the refactoring that exposes it and propose it to the user before proceeding. Done when: the code's algebraic shape is named (inverse, invariant, idempotence, oracle, roundtrip, commutativity, associativity, identity, or determinism), or the shape is absent and the stop recommendation is stated.
- Determine which property applies. Use the property catalog and strength ordering:
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.
- 6d ago First seen · 79 lines · 57 tokens per session scan A 7fafb5e4b9ce
property-test-authoring is a skill published in the GitHub repository OutlineDriven/odin-claude-plugin (35 stars, last pushed today), licensed Apache-2.0. It adds 57 tokens to every session and 1,765 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 2026-09-04.
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