A coding guide for building interfaces with coss, a UI component library based on Base UI. It explains which components to use, how to combine them, and how to avoid common mistakes when moving from shadcn or Radix.

Use it to build buttons, dialogs, selects, forms, menus, tabs, inputs, toasts, and other coss-based interface elements, or to migrate an existing shadcn or Radix UI.

It helps prevent incorrect component usage, broken interactions, and accessibility problems when building with coss components.

How crafter-station/petdex configures Claude Code and Codex

About the project

Petdex is a gallery, installer, and desktop application for animated pets that accompany coding agents. People browse and submit pets through its website, install them with a command-line tool, and use the desktop app to display reactions to agent activity. The catalogue includes skills and instructions for creating or using these pets with supported coding agents.

crafter-station/petdex · 4,283 stars · on GitHub · petdex.dev

Reuse

Borrowing it

Nothing to install: this file belongs to crafter-station/petdex. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/crafter-station/petdex/main/.agents/skills/coss/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/crafter-station/petdex

Made for: Claude Code, Codex.

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/crafter-station/petdex/coss/github.svg)](https://agentmods.dev/skills/crafter-station/petdex/coss)

Your own site

<a href="https://agentmods.dev/skills/crafter-station/petdex/coss"><img src="https://agentmods.dev/badge/skills/crafter-station/petdex/coss/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/crafter-station/petdex/coss"><img src="https://agentmods.dev/badge/skills/crafter-station/petdex/coss.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 80 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,211 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.

Origin 95% copy Near-identical to another mod 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	$0.00080	$0.01211
Opus 5.5	$0.00032	$0.00484
Sonnet 5.5	$0.00016	$0.00242
Haiku 4.5	$0.00008	$0.00121

Measured 1mo ago against content hash e5a1362ea005, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

coss 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.

Origin

This is a copy

95% identical to coss — 1 line differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.agents/skills/coss/SKILL.md · 118 lines

How it starts

The opening of the file, as written. The whole thing — 118 lines — stays where its author put it; the contents beside it link to each section on GitHub.

coss ui

coss ui is a component library built on Base UI with a shadcn-like developer experience plus a large particle catalog.

What this skill is for

Use this skill to:

pick the right coss primitive(s) for a UI task
write correct coss usage code (imports, composition, props)
avoid common migration mistakes from shadcn/Radix assumptions
reference particle examples to produce practical, production-like patterns

Source of truth

coss components docs: apps/ui/content/docs/components/*.mdx
- https://github.com/cosscom/coss/tree/main/apps/ui/content/docs/components
coss particle examples: apps/ui/registry/default/particles/p-*.tsx
- https://github.com/cosscom/coss/tree/main/apps/ui/registry/default/particles
coss particles catalog: https://coss.com/ui/particles
docs map for agents: https://coss.com/ui/llms.txt

Out of scope

Maintaining coss monorepo internals/build pipelines.
Editing registry internals unless explicitly requested.

Principles for agent output

Use existing primitives and particles first before inventing custom markup.
Prefer composition over custom behavior reimplementation.
Follow coss naming and APIs from docs exactly.
Keep examples accessible and production-realistic.
Prefer concise code that mirrors coss docs/particles conventions.
Assume Tailwind CSS v4 conventions in coss examples and setup guidance.

Critical usage rules

Always apply before returning coss code:

Do not invent coss APIs. Verify against component docs first.
For trigger-based primitives (Dialog, Menu, Select, Popover, Tooltip), follow each primitive's documented trigger/content hierarchy and composition API; do not mix patterns across components.
Preserve accessibility labels and error semantics.
Consult primitive-specific guides for component invariants and edge cases.
For manual install guidance, include all required dependencies and local component files referenced by imports.
Prefer styled coss exports first; use *Primitive exports only when custom composition/styling requires it.

Read the full file on GitHub · 118 lines

Files

What ships with it

60 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.

1mo ago First seen · 118 lines · 80 tokens per session scan A e5a1362ea005

Subscribe to this mod's changes

coss is a skill published in the GitHub repository crafter-station/petdex (4,283 stars, last pushed 15d ago), licensed MIT. It adds 80 tokens to every session and 1,211 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 95% identical to coss, differing in 1 line, and is treated as a copy.

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Review UI code for Web Interface Guidelines compliance. Use when asked to "review my UI", "check accessibility", "audit design", "review UX", or "check my site against best practices".

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Mandatory design-brief gate for clarifying the product and outcome. Use before ideation, image-to-code builds, redesigns, or product UI work to clarify missing product information and play back the brief before proceeding.

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Builds, styles, and polishes anything drawn with HTML, CSS, or SVG: web UI, pages, components, HTML reports rendered to PDF or print, figures, PNG/SVG diagrams, slides, and images for Notion or Slack. Use for any styling, layout, animation, or visual-quality task, or when asked to make something look or feel a certain…

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petdex: Skill for Claude Code