Visually Explain

Turn a specific mechanism from the codebase into a single self-contained interactive HTML document that you can open in a browser and play with. For a visual learner, a toggle that flips between "what happens now" and "what should happen", or a stepper that walks a real example through each state, lands an idea that no paragraph can.

The artifact is the explanation. Prose annotates it; it doesn't carry it. If the result reads like a Markdown doc that happens to be wrapped in <div>s, it failed.

When this runs

Invoked explicitly with /visually-explain — it is never auto-triggered by a bare conceptual question. If someone just asks "how does X work?", answer in prose; you may offer to build an explainer, but only build on an explicit ask. Producing the artifact writes a file and opens a browser tab, so opting in should be deliberate.

Scope: codebase/spec-grounded only. This skill explains a particular system you can point at — the actual code, a design doc, a spec. It is not for general-concept tutorials ("explain how operational transform works in the abstract"). Without a concrete source to verify against, there's nothing to keep the visual honest, and honesty is the whole point (below). If the request is a general-concept explainer, say so and stop.

Correctness is the whole job (non-negotiable)

This is the one rule that overrides everything else in this skill. An interactive visual looks authoritative -- polished layout, confident color-coding, smooth transitions all signal "this is right". That makes a wrong explainer far more dangerous than wrong prose: the reader trusts it and builds a broken mental model on top. A bad or buggy explanation is worse than none at all.

So:

• Never guess, never hallucinate, never smooth over a gap. If you don't fully understand a mechanic, you cannot visualize it. Don't invent how something works to make a cleaner animation or a tidier diagram.
• Don't visualize anything you can't verify. Every state transition, index shift, color, and label must be something you've confirmed from the source -- the code, the spec, the user -- not inferred because it seems plausible.
• When you're unsure, stop and ask (or leave it visibly out). It is correct and expected to tell the user "I don't understand X well enough to draw it truthfully -- can you clarify, or should I leave it out?" That is a success, not a failure.
• Mark genuine uncertainty in the artifact itself. If something is your best-effort interpretation rather than confirmed fact, label it as such in the document (e.g. a dimmed "assumption" tag) so the reader never mistakes a guess for ground truth. Better still: resolve it first.
• Keep it simple, because simplicity is what makes it trustable. Simplicity here is not an aesthetic preference — it's a correctness requirement. Every bit of cleverness (more states, more moving parts, more computed logic) is extra surface where the explanation can quietly go wrong. A simple visual you can fully stand behind beats an elaborate one you can't. When in doubt, show less, more correctly.

There is no partial credit for a beautiful diagram that's subtly false.

First, actually understand the thing

You cannot visualize what you don't understand. Garbage in, garbage out.

Before writing any HTML: read the code, the design, the thread -- whatever the concept lives in. Trace the concrete worked example through by hand and confirm each state is what the real system would actually produce.

The source is the authority, not the user. You're usually invoked precisely because the user doesn't fully understand the thing yet — so don't quiz them to reconstruct it. Read the code, build from it, and keep questions minimal. Default to building. Only stop to ask when your hand-trace hits something genuinely ambiguous that changes the visual and you can't resolve it from the source and getting it wrong would make the visual false. That one high-stakes point is worth a quick confirm (or an "assumption" tag); everything else, just build it.

When you're confident you understand it, find the one concrete worked example that exposes the heart of the idea -- the smallest input that still shows the interesting behavior. The screenshot that inspired this skill threads "Hello" through two concurrent edits to show exactly where client-side rebasing diverges. That single example does more than three paragraphs of theory. Pick yours before you design anything.

Choose an interaction that fits the concept

The interaction is not decoration -- it's how the reader builds the mental model. Match it to what the concept actually is:

• Compare toggle / tabs -- flip the same state between two readings: "current behavior" vs "intended result", naive vs correct, before vs after a fix. Best when the whole point is a divergence.
• Stepper / timeline -- walk one concrete example through sequential states (Initial -> Client A -> Server -> ...), forward and back. Best for protocols, algorithms, request lifecycles, anything with ordered causality.
• Side-by-side -- two approaches running the same scenario in parallel (client-side rebasing vs server-side rebasing). Best for "why this design over that one".
• Annotated state -- render the domain object concretely (text as boxed characters, a queue as cells, a tree as nodes) and color-code roles: accepted/green, deleted/red, stale/amber, new/blue. The reader should see the state, not read a description of it.
• Diff / highlight -- show what changed between two states, with the delta emphasized and the unchanged parts dimmed.
• Progressive reveal -- expandable detail for layered ideas, so the overview stays uncluttered and depth is opt-in.
• Live playground -- let the reader change an input and watch the result recompute. The most powerful option when the concept is a transformation, and worth the extra effort when it is.

Combine them when it serves the idea (a stepper with a compare toggle at each step is exactly the screenshot's pattern). Don't combine them to show off.

Bake in pre-computed states; don't trust live JS

There are two independent ways the visual can lie: you can misunderstand the system (covered above), or your inline JS can be buggy — the stepper shifts an index wrong, a computed state comes out subtly off — so the explanation is false even though your mental model was right.

So by default, bake in the states you traced by hand. The states are data you already verified; the JS just reveals them step by step. A dumb presenter over hand-checked data has almost nothing to get wrong. This is the same simplicity = trust principle: the less the artifact computes, the less it can fool you with.

A live playground that recomputes from arbitrary user input is the opposite — a whole new program that must itself be correct, running on inputs you never traced. Reserve it for when the concept genuinely is a transformation worth playing with, and when you do reach for it, verify the computed output against your hand-traced example before shipping — e.g. run the logic in Node and confirm it reproduces the known-correct sequence. Never trust live computation blind.

Aesthetics

This skill owns what to show and how it behaves, not how it looks. If the frontend-design skill is available, invoke it (via the Skill tool) for typography, color, motion, and composition before styling — don't just nod at it.

It may not be installed, though (this skill ships standalone), so here's a self-sufficient fallback guardrail when it isn't:

• Distinctive but legible. No generic AI slop — no Inter/Arial, no purple-gradient-on-white. Pick type and color with intent.
• Restraint over flash. The simplicity that makes the artifact trustable also makes it look considered. Don't drown the explanation in effects.

Two domain-specific rules apply on top either way:

• Color must encode meaning, not just look nice. If green means "accepted" in one place, it means "accepted" everywhere. Keep a tiny, legible legend.
• Motion should clarify causality (a character sliding as an index shifts), never just animate for delight. A transition that shows why an index moved is worth it; a fade-in for its own sake is noise.

Self-contained, always

One .html file. All CSS and JS inline. No build step, no framework, no network calls -- the user double-clicks it, or opens it on a plane, and it just works. Vanilla JS and CSS are plenty for these; reach for nothing heavier.

The single tolerable exception is one web font from a CDN -- and only with a real system fallback in the stack so it degrades gracefully offline. Everything else (icons, logic, state, styles) ships in the file.

You can't see the render — split the work honestly

You write the HTML, but it opens in the user's browser, not yours. You can verify the data (the states are correct) by reading your own code; you cannot verify the rendering — that step 3 shows the right state, that the colors landed, that nothing overflows. So own what you can and hand off what you can't: you're responsible for truth-of-data, the user is your eyes on the visual. Never claim it "looks good" — you haven't seen it. Ask them to open it and flag anything off, then iterate. (If headless tooling like Playwright already exists in the project, a quick self-screenshot is a fine bonus check — but don't add it as a dependency.)

Output

Write the file to the current working directory with a sensible name derived from the topic (e.g. livetext-rebasing.html), then open it:

open livetext-rebasing.html

It's a throwaway artifact — an understanding aid, not a committed doc. Leave it in cwd for the user to keep or rm; never commit it. On revisions, overwrite the same file and re-open.

What goes in the chat. The artifact carries the explanation — don't re-explain the concept in prose (that's a redundant second copy to keep in sync). The chat carries only what the file can't speak for itself:

• The filename, and that it's opened.
• A short guided walkthrough — how to drive the visual to the interesting moment: "press Intended result, then step to the second Server row — that's where B's index goes stale." Point them straight at the aha, and note any subtlety about operating it.
• Any assumptions or unverified points you flagged, and anything specific you want them to eyeball ("does step 3 match what you'd expect?").

Smell test before you ship

• Is every single thing in it true and verified? Can you point to where each state, transition, and label comes from in the source? Any "I think it works like this" must be resolved or visibly marked as an assumption -- never shipped as fact. This gate comes first; a wrong artifact fails regardless of how good it looks.
• Are the displayed states baked-in hand-verified data, or computed live? If computed, have you run the logic and confirmed it reproduces the traced example?
• Could a reader get the core idea from the visual alone, with the prose hidden? If not, the visual isn't doing its job yet.
• Is there a real worked example, or just abstract boxes labeled "State A"?
• Does every color and animation mean something?
• Is it as simple as it can be? Could any state, control, or effect be removed without losing the point — and would removing it make the rest more trustable?
• Does it open offline by double-clicking, with nothing fetched?
• Is it one focused concept, not a sprawling tour? One artifact, one idea.