Diagnosing UI Agent Skill

UI branch of the diagnosing loop. Use when debugging any UI bug — wrong rendering, layout or scroll jumps, flicker, styling, interaction…

Context cost
2.4k tokensestimated from the bundle, loaded when it triggers
Bundle
1 file · 9.4 kBtext throughout, nothing executable
Licence
MITthe author’s own terms
Last change
—no release on file
Servers it uses
Noneruns standalone

What it does

UI branch of the diagnosing loop. Use when debugging any UI bug — wrong rendering, layout or scroll jumps, flicker, styling, interaction, focus/attention, or reactivity failures — in Composer plugins, react-ui components, storybook stories, or the running app. Applies from the first symptom report, before proposing any fix.

What this skill changes about the agent has not been set out here as a list. Its SKILL.md, shown below, says it in the author’s own words.

debuggingdesign
Filed under

Design & Media

The skill itself

A skill is instructions the model reads, so you can see what you are getting: below is the start of its SKILL.md. The front matter loads with every session, the body loads when the skill triggers, and the whole file comes with the install.

SKILL.md9.4 kB · preview
--- name: diagnosing-ui ---
6# Diagnosing UI
7
8The UI branch of the diagnosing-bugs skill. That loop governs — repro contract first, tight red loop, minimise, 3–5 ranked hypotheses, golden rule after every change. This skill adds what is specific to bugs a browser renders: the instrument table, the isolation ladder, the verification contract, and the interaction budget.
9
10Forked from the dxos repo's debugging-ui, with the generic phases evacuated into diagnosing-bugs.
11
12## Core principle
13
14**The user is the most expensive and least available instrument you have.** Every verification you can perform yourself — running a test, driving a browser, reading a frame trace — is strictly cheaper than asking the user to look. A debugging process that consumes user round-trips is a failing process even when it eventually finds the bug. One real session burned 13 user test-asks over 21 hours; every correction that worked came from the user, not the agent. This skill exists so that never happens again.
15
16Violating the letter of these rules is violating their spirit.
17
18## Instruments
19
20| Instrument | Use for |
21| ------------------------------------------ | ---------------------------------------------------------------- |
22| Unit tests (vitest) | State/logic isolation; cheapest repro |
23| Storybook stories + play scripts | Component/container behavior; deterministic fixtures |
24| Playwright / browser MCP against storybook | Gestures, frame traces, console, screenshots |
This is a preview of SKILL.md. Download or install the skill to get the whole thing.
In the file
SKILL.md1,388 words
Files1
LicenceMIT
Why you can read it

Nothing in a skill executes. The client loads the text and the model follows it, so a skill can be audited the way a runbook is — by reading it.

What it costs in context

Skills are not billed by the call. They are paid for in context: every token the instructions occupy is a token your code, your diff and your conversation cannot use. Here is what this one takes and when it takes it.

≈90
always loaded
The name and description, so the model knows the skill exists and when to reach for it.
2,260
on trigger
The instruction body, read only when the skill fires.
1.2%
of a 200k window
Ten skills this size would take about 12% of the window before you open a file.
050k100k150k200k context window

2.4k tokens, estimated from the bundle at four bytes to the token, held for the rest of the session once it triggers. Middling. Fine to keep on in a project where you use it weekly, worth unloading in one where you never do.

Servers bill, skills cost

A server charges by the month. A skill charges once per session, in context, and then keeps charging it for as long as the session lives.

Before and after

The same question, put to the same model twice: once as it comes, and once with these instructions loaded.

No worked example has been published for this skill yet.

The procedure it runs

The procedure has not been set out here step by step. It is in the body of its SKILL.md: the start of it is shown above, and the whole file comes with the install.

Prose, not code

These steps are written for a model to follow, not executed by a runtime. It can still be told to skip one, and it will say so when it does.

Servers it uses

None. This skill calls no MCP servers at all.

Everything it needs is in the instructions, so it works in a project with nothing connected — the model reads the file and changes how it works with what it can already reach.

Its SKILL.md does not declare which tools it asks the agent for, so what it touches is whatever the instructions themselves ask for — read them before you install it.

What it asks for
Writes filesnot declared
Network accessnot declared

This SKILL.md carries no allowed-tools line, so neither is declared. A skill grants no permissions of its own — it can only ask for tools your client already has.

What it will not do

Every skill is narrow, and the useful ones say where they stop. These are the jobs this one is the wrong tool for.

What this skill is not for has not been published here. Nothing is implied by that: it is a section the author has not filled in.

What is in the bundle

1 file, 9.4 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

  • SKILL.md9.4 kB
What is not in it

No dependencies and nothing executable: a skill is text the agent reads, so the bundle is 1 file you can review in full before installing. The MIT licence covers the templates and examples as well as the instructions.

Install

Installing copies the bundle into your project. Nothing runs at install time — the files sit on disk until the model reads them.

# Diagnosing UI · 2.4k tokens when loaded · macOS, Linux mkdir -p .claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/diagnosing-ui/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/diagnosing-ui" ] && { [ ! -e .claude/skills/diagnosing-ui ] || { mv .claude/skills/diagnosing-ui "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/diagnosing-ui" .claude/skills/ && echo "Installed .claude/skills/diagnosing-ui"
On Windows, or any OS with Node 20+
npx mcprush@latest skill add wittjosiah/diagnosing-ui

Windows PowerShell says 'running scripts is disabled on this system'? Run Set-ExecutionPolicy -Scope CurrentUser RemoteSigned once, or type npx.cmd instead of npx (codex.cmd, gemini.cmd, grok.cmd likewise). PowerShell 7 needs neither. Writes to .claude/skills/diagnosing-ui/ in the current project. For every project instead, run mkdir -p ~/.claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/diagnosing-ui/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/diagnosing-ui" ] && { [ ! -e ~/.claude/skills/diagnosing-ui ] || { mv ~/.claude/skills/diagnosing-ui "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/diagnosing-ui" ~/.claude/skills/ && echo "Installed ~/.claude/skills/diagnosing-ui" (macOS, Linux) — or add --global to the npx line. The curl line replaces .claude/skills/diagnosing-ui/ only after the download succeeds, so files left there by another skill of the same name, or by an older release, do not mix in. A copy already there is moved aside, not deleted, and the line prints where.

Which clients pick it up on their own

A skill is a folder of text. Most of these read a skills folder and pick it up without being told; the rest take the same folder another way — an upload in the app, a parameter on an API call — and then choose it by its description just the same.

Claude Code.claude/skills/
Claude DesktopCustomize › Skills
ChatGPTSkills › Create › Upload
Cursor.cursor/skills/
VS Code.github/skills/
Codex CLI.agents/skills/
Gemini CLI.gemini/skills/
Grok Build.grok/skills/
Microsoft CopilotSkills › Upload a skill
PerplexityComputer › Skills › Upload a skill
DeepSeek Harness.dsh/skills/
Zed.agents/skills/
Devin Desktop.devin/skills/
Windsurf (legacy).windsurf/skills/
OpenAI Agents SDKInstructions or sandbox Skills
HTTP / APIa request parameter
This release
Versionnot versioned
Publishedno release date on file
PriceFree
Referencewittjosiah/diagnosing-ui

Versions

Its author publishes no version number, so there is nothing here to pin to: what you install is the folder as it stands today. Instructions change more often than APIs do — a skill can be rewritten entirely without anything it depends on moving.

Pinning

Nothing to pin to: this skill carries no version number of its own. What you install is what the folder holds on the day you install it.

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