Individual skill
mr-null
Reserved-string and numeric-coercion check, inspired by the Big List of Naughty Strings. Finds where literal "null", "undefined", "None", "NaN", "__proto__", "NO", 1E02, 0x10, -0, or a 17-digit ID become a blank field, a wrong number, or a crash. Types each case into a live test environment's forms and submits it, checking client validation, the server response, and the saved value; or reviews the repo's parsing code. No signup.
skills/mr-null/SKILL.md
Source commit e17f9081b1b1746a837bb188f6ef3245d720fc4b
What was checked
- Matches the observed repository HEAD
- Yes
- Scanner rules are current
- Yes
- Repository scan complete
- No
- Skill scan complete
- No
- Observed behavior
- Instructions only
- Last checked
- Nov 11, 2026
These are observations at the recorded commit, not a guarantee of safety. Review the source before running it.
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An install command is unavailable: current rules, complete repository and skill scans, an eligible behavior level and a permitted license are required.
Repository context
- Repository stars (not skill ratings)
- 13
- Repository last updated
- Nov 1, 2026
- License
- Apache-2.0
Observed agent integration: No specific integration evidence. Standard SKILL.md installation does not imply verified compatibility.
- accessibility Repository topic
- claude-code Repository topic
- code-review Repository topic
- core-web-vitals Repository topic
- playwright Repository topic
- privacy Repository topic
- qa Repository topic
- quality-assurance Repository topic
- security Repository topic
- seo Repository topic
- testing Derived category
Files and excerpt
File metadata and permitted, redacted excerpts come from the recorded scan. Source links are pinned to that commit.
Read excerpt
# Mr. Null
Your app has never met a user named Null. Mr. Null has met your app.
People really are called Null, there really is a country code `NO`, and someone will
paste `1E02` into your quantity box. This skill finds the places where a string that
happens to look like a keyword or a number gets treated as one.
## Prerequisites
- **Website mode:** Playwright MCP (comes with Claude Code).
- **Repository mode:** none. Reads local files directly.
## Trigger