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 Notysoty/openagentskills --skill edge-case-discoverygit clone --depth 1 https://github.com/Notysoty/openagentskillsWrote 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/notysoty/openagentskills/edge-case-discovery)<a href="https://agentmods.dev/skills/notysoty/openagentskills/edge-case-discovery"><img src="https://agentmods.dev/badge/skills/notysoty/openagentskills/edge-case-discovery/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/notysoty/openagentskills/edge-case-discovery"><img src="https://agentmods.dev/badge/skills/notysoty/openagentskills/edge-case-discovery.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 | $0.00022 | $0.01705 |
| Opus 5.5 | $0.00009 | $0.00682 |
| Sonnet 5.5 | $0.00004 | $0.00341 |
| Haiku 4.5 | $0.00002 | $0.00170 |
Grade A, and why
Edge Case Discovery 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 1mo 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 — 180 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Edge Case Discovery
What this skill does
This skill directs the agent to systematically work through a function, API endpoint, or user flow and enumerate all edge cases and boundary conditions that could cause incorrect behavior, errors, or security issues. It applies a structured checklist across multiple dimensions (data types, boundary values, state, concurrency, authorization) and outputs a prioritized list of cases to test or guard against.
Use this before writing tests, during code review, when designing a new feature, or when a production bug makes you wonder "what else could go wrong here."
How to use
Claude Code / Cline
Copy this file to .agents/skills/edge-case-discovery/SKILL.md in your project root.
Then ask:
- "Use the Edge Case Discovery skill on the
transferFundsfunction." - "Find edge cases for the
POST /api/ordersendpoint using the Edge Case Discovery skill." - "What edge cases should I handle in the user registration flow? Use the Edge Case Discovery skill."
Provide the function signature, the code, or a description of the flow.
Cursor
Add the instructions below to your .cursorrules or paste them into the Cursor AI pane before sharing the function or flow you want analyzed.
Codex
Paste the function or flow description and ask Codex to follow the instructions below to generate the edge case list.
The Prompt / Instructions for the Agent
When asked to discover edge cases, apply the following checklist systematically. Not every dimension applies to every input — skip the ones that clearly don't apply and note why.
Dimension 1 — Numeric inputs
For every numeric input or value in the function/flow:
- Zero (0)
- Negative numbers
- Maximum safe integer / maximum allowed value
- Minimum allowed value
- Values just above and just below each boundary (boundary value analysis)
- Non-integer values when integers are expected
- Infinity / NaN (for floating-point)
- Very large numbers that could cause overflow or performance issues
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.
- 1mo ago First seen · 180 lines · 22 tokens per session scan A adaebe104360
Edge Case Discovery is a skill published in the GitHub repository Notysoty/openagentskills (9 stars, last pushed 2mo ago), licensed MIT. It adds 22 tokens to every session and 1,705 once invoked, about $0.0001 per session on Opus 5.5. 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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