Front-End Checklist is a collection of front-end web development rules organized as a practical review and quality workflow for people and AI agents. Developers use it to audit projects and pull requests, check implementation details, and find guidance for remediation and verification. The catalogue entries provide skills, instructions, MCP tools, and a plugin for using the checklist in agent workflows.
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 thedaviddias/Front-End-Checklist --skill css-at-propertygit clone --depth 1 https://github.com/thedaviddias/Front-End-ChecklistWrote 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/thedaviddias/front-end-checklist/css-at-property)<a href="https://agentmods.dev/skills/thedaviddias/front-end-checklist/css-at-property"><img src="https://agentmods.dev/badge/skills/thedaviddias/front-end-checklist/css-at-property/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/thedaviddias/front-end-checklist/css-at-property"><img src="https://agentmods.dev/badge/skills/thedaviddias/front-end-checklist/css-at-property.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 | $0.00035 | $0.00437 |
| Opus 5.5 | $0.00014 | $0.00175 |
| Sonnet 5.5 | $0.00007 | $0.00087 |
| Haiku 4.5 | $0.00003 | $0.00044 |
Grade A, and why
css-at-property 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 23d 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.
What it actually says
Register CSS custom properties with @property for animation and type safety
CSS custom properties are powerful but limited by default: they are untyped string substitutions that the browser cannot interpolate during transitions or animations. Registering a property with @property gives the browser the information it needs to animate between values, validate token assignments, and scope inheritance — turning custom properties from string macros into first-class typed values. This unlocks gradient animations, typed design tokens, and scoped component theming that are impossible with unregistered properties.
Quick Reference
- Unregistered custom properties cannot be animated — they transition as discrete strings
- @property specifies syntax (color, length, number), initial-value, and inherits
- Registered properties enable smooth interpolation for gradients and complex values
- inherits: false creates scoped tokens that do not cascade to children
Check
Review the CSS custom properties in this file. Identify any properties that are used in transitions or animations — these require @property registration to animate correctly.
Fix
Add @property registrations for the custom properties used in transitions or animations in this CSS. Include the correct syntax descriptor, an initial-value, and the appropriate inherits value.
Explain
Explain how @property works, why unregistered custom properties cannot be animated, what the syntax descriptor values mean, and how inherits controls cascade behaviour.
Code Review
Inspect all CSS transitions and animations that reference custom properties. Flag any custom property used in a transition or animation that is not registered with @property, and flag any @property registration that is missing initial-value.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/css/css-at-property
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.
- 23d ago Changed f1e1da6dc3f3
- 1mo ago First seen · 46 lines · 35 tokens per session scan A 515aa3ab88dd
css-at-property is a skill published in the GitHub repository thedaviddias/Front-End-Checklist (74,577 stars, last pushed 21d ago), licensed MIT. It adds 35 tokens to every session and 437 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 2026-09-03.
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