What is 21st-ui-review?

A guide for reviewing an existing website interface for accessibility, responsive behavior, interaction quality, design consistency, and clear production defects.

Auditing components and pages, checking keyboard and screen-reader access, responsive layouts, images, menus, dialogs, loading states, and safely fixing clear defects.

It helps developers distinguish code-backed usability problems from subjective design suggestions and gives each finding a location and priority.

21st-ui-review — Skill for Claude Code and Codex by 21st-dev: A guide for reviewing an existing website interface for…

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/21st-dev/skill/21st-ui-review

Any agent

npx skills add 21st-dev/skill --skill 21st-ui-review

Clone the repo

git clone --depth 1 https://github.com/21st-dev/skill

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/21st-dev/skill/21st-ui-review.svg)](https://agentmods.dev/skills/21st-dev/skill/21st-ui-review)

Your own site

<a href="https://agentmods.dev/skills/21st-dev/skill/21st-ui-review"><img src="https://agentmods.dev/badge/skills/21st-dev/skill/21st-ui-review.svg" alt="Measured on agentmods" height="20"></a>

Per session 103 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 437 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin 100% 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	$0.00103	$0.00437
Opus 5	$0.00051	$0.00218
Sonnet 5	$0.00021	$0.00087
Haiku 4.5	$0.00010	$0.00044

Measured 4d ago against content hash 78939e830bce, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

21st-ui-review 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 4d 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

100% identical to 21st-ui-review — 0 lines 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.

skills/21st-ui-review/SKILL.md · 50 lines

What it actually says

Review UI with evidence

Separate deterministic defects from subjective design recommendations.

Workflow

Read .21st/design.json, project instructions, and the relevant source.

Run the deterministic review first:

21st review <path>
21st review <path> --json

Inspect the actual component composition and runtime states. Validate claims against code rather than inferring behavior from names.
Group findings into:
- deterministic defects;
- design-system drift;
- accessibility and interaction defects;
- responsive risks;
- subjective product/design recommendations.
Prioritize by user impact and include exact file and line attribution.
Use 21st review <path> --fix only for deterministic, low-ambiguity fixes. Never silently redesign, change brand identity, or alter product behavior.
Run relevant project tests after fixes and rerun review to prove resolution.

Review priorities

semantic controls and accessible names;
keyboard access, focus visibility, and dialog/menu behavior;
image alternatives and meaningful labels;
touch target size and disabled/loading states;
responsive overflow and fixed-width assumptions;
reduced-motion handling;
hardcoded visual values that conflict with project tokens;
duplicate primitives instead of existing components;
inconsistent typography, radius, spacing, shadows, and icons;
fake data, placeholder copy, or missing empty/error states.

Output

Lead with actionable findings ordered by severity. Keep subjective suggestions clearly labeled. If no issue is proven, say so and state what was inspected.

Files

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.

agents/openai.yaml 200 B

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.

4d ago First seen · 50 lines · 103 tokens per session scan A 78939e830bce

Subscribe to this mod's changes

21st-ui-review is a skill published in the GitHub repository 21st-dev/skill (4 stars, last pushed 9d ago), licensed Apache-2.0. It adds 103 tokens to every session and 437 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to 21st-ui-review, differing in 0 lines, and is treated as a copy.

Design and UX

html-ppt-hermes-cyber-terminal

OpenDesign + BYOK: choosing and wiring your own model, hands-on — cost, quality, and the routing decision. Built as a decision-grade AI literacy deck for engineers, IT, applied-AI teams.

nexu-io/open-design · 53 tokens

html-ppt-taste-brutalist

16:9 HTML deck in tactical-telemetry / CRT-terminal taste. Deactivated-CRT charcoal slides, white-phosphor monospace, hazard-red accent, scanline overlay, ASCII syntax, density over decoration. Distilled from Leonxlnx/taste-skill brutalist-skill (Tactical Telemetry mode).

nexu-io/open-design · 78 tokens

21st-ui-review