coss-ui

A setup and extension guide for Coss/UI, Cal.com's interface design system, in Next.js projects. It covers installing its components and keeping their design values aligned with `DESIGN.md`.

In plain words
What is it for?
Use it to initialize Coss/UI, add its interface components, or reconcile Coss/UI design values with a project's design specification.
Why use it?
It gives the project a defined way to add Coss/UI components without guessing package commands or registry settings. It also separates interface-library work from the general app scaffold.

Skill for Claude CodeCodex

Part of the dev-flow plugin — 45 skills shipped together

Install

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.

agentmods
npx agentmods add skills/lukedj78/dev-flow/coss-ui
Any agent
npx skills add lukedj78/dev-flow --skill coss-ui
Clone the repo
git clone --depth 1 https://github.com/lukedj78/dev-flow

Made for: Claude Code, Codex.

Or install dev-flow, the plugin that ships this one along with the rest of its 45 skills.

Per session 244 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,364 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found 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.

ModelPer sessionOnce invoked
Fable 5 $0.00244 $0.02364
Opus 5 $0.00122 $0.01182
Sonnet 5 $0.00049 $0.00473
Haiku 4.5 $0.00024 $0.00236

Measured 3d ago against content hash cf68b85cf816, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

coss-ui 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 3d ago.

The scan reads SKILL.md. This mod also ships 2 executable files (scripts/check_coss_state.py, scripts/test_check_coss_state.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

coss-ui/SKILL.md · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

coss-ui — Coss/UI (Cal.com design system) for a dev-flow project

This skill owns the Coss/UI side of a web project: installing and extending Coss components (the Cal.com design system on Base UI + Tailwind v4) through the shadcn CLI @coss/* registry, and keeping Coss's tokens reconciled with the project's DESIGN.md. It composes with design-md-to-app (which owns the generic Next.js scaffold) — it does not re-implement it.

The one rule that matters most

Never invent the Coss commands or registry. The source of truth is the live docs at https://coss.com/ui/docs (get-started + each component page shows its exact pnpm dlx shadcn@latest add @coss/<name> command) and the repo cosscom/coss. Confirm the exact command, the components.json#registries config for the @coss namespace, and the current registry URL before running anything. Coss is young; treat this skill as the workflow + conventions, not a frozen copy of the API. Swept 2026-08-26 against the live registry (coss.com/ui/r/registry.json — 577 items — plus style.json, ui.json and the three font items), so the counts, the namespace requirement and the font slots below are read from the registry rather than the docs page. Anything still marked [VERIFY] must be checked against the live docs first.

Why Coss fits dev-flow (and when to pick it)

Coss/UI rides the same machinery dev-flow already uses: shadcn CLI v4 + components.json + CSS-variable tokens with the same names as shadcn/ui. So the DESIGN.md → tokens pipeline works unchanged; Coss just supplies the default token set (@coss/colors-neutral) plus a curated Base-UI component/particle registry. It is a UI-library choice inside the shadcn / Base-UI family, recorded as stack.ui = "coss" (with ui_base = "base", since Coss is built on Base UI).

Pick Coss when the user wants the Cal.com aesthetic/DX, a Base-UI foundation, and an AI-first copy-paste kit. Two caveats make it a deliberate choice, not a default:

Read the full file on GitHub · 96 lines

Files

What ships with it

6 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.

  1. 3d ago First seen · 96 lines · 244 tokens per session scan A cf68b85cf816

Subscribe to this mod's changes

coss-ui is a skill published in the GitHub repository lukedj78/dev-flow (5 stars, last pushed 5d ago), licensed MIT. It adds 244 tokens to every session and 2,364 once invoked, about $0.0012 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 2026-08-31.

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