Flutter Performance Agent Skill

Enforces Flutter runtime performance — const subtrees, minimal rebuild scope via ref.watch(select), lazy ListView/GridView builders and…

Context cost
2.5k tokensestimated from the bundle, loaded when it triggers
Bundle
1 file · 9.9 kBtext throughout, nothing executable
Licence
MITthe author’s own terms
Last change
—no release on file
Servers it uses
Noneruns standalone

What it does

Enforces Flutter runtime performance — const subtrees, minimal rebuild scope via ref.watch(select), lazy ListView/GridView builders and slivers, sized image decode (cacheWidth/ResizeImage), heavy work off the UI isolate via compute/Isolate, surgical RepaintBoundary, dispose everything, and measurement in profile mode on a floor device. Use when optimizing UI, diagnosing jank or dropped frames, tuning long lists or images, reviewing rebuild/repaint scope, or when the task mentions const, select, ListView.builder, cacheWidth, compute, RepaintBoundary, AnimatedBuilder, DevTools, raster thread…

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.

fluttermobileperformance

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.md9.9 kB · preview
--- name: flutter-performance ---
6# Flutter Performance
7
8Hold a steady 60 fps (<=16 ms/frame; <=8 ms on 120 Hz) on a floor device (low-end Android / older iPhone). Performance is a property you **measure in profile mode**, not one you assert. It comes from rebuilding less, painting cheaply, and keeping both the UI thread and the raster thread free.
9
10## Non-negotiable rules
11
121. **const everything legal.** A const subtree is skipped on rebuild — the framework short-circuits it by identity. Keep prefer_const_constructors on as an error; a non-const literal that could be const is a lint failure, not a preference.
132. **Shrink the rebuild scope to the smallest changing widget.** Never ref.watch(provider) for a whole state object when one field changed — watch provider.select((s) => s.field). A HUD counter tick must never rebuild a heavy sibling. Rebuild scope is the single biggest lever on build-thread cost.
143. **Lazy everything long.** ListView.builder / GridView.builder / slivers for variable or unbounded content. ListView(children: items.map(...).toList()) builds every off-screen row up front — refuse it for anything not tiny and fixed.
154. **No expensive work in build().** No jsonDecode, sort, regex, DateTime math, file/network, or large allocation — build() may run every frame. Compute in the Notifier/ViewModel once and cache the result in immutable state.
165. **Heavy CPU off the UI isolate.** Parse large payloads, process images, crunch numbers in compute() or a spawned Isolate. Blocking the UI thread is guaranteed jank; the raster thread cannot save you.
176. **Size image decode to the display slot.** cacheWidth/cacheHeight or ResizeImage, correct asset resolutions, precacheImage for above-the-fold art. Decoding a 4000 px source into a 100 px box spikes memory and OOMs cheap phones.
187. **Prefer the cheapest widget that does the job.** ColoredBox/DecoratedBox over Container, SizedBox for spacing, FadeTransition/AnimatedOpacity over the Opacity widget in hot paths. Avoid ClipPath/saveLayer inside scrolling lists — they force an offscreen buffer on the raster thread.
198. **RepaintBoundary around costly, independently-repainting subtrees** (an animation, a chart, a live indicator) so its repaint does not re-raster its neighbours. Do not sprinkle boundaries everywhere — each is a compositor layer that costs memory.
209. **Pass expensive children through child:.** AnimatedBuilder/ValueListenableBuilder/StreamBuilder rebuild only the builder; hand the unchanging subtree in via child: so it is built once, not per frame.
2110. **Dispose to avoid leaks.** AnimationControllers, gesture recognizers, stream subscriptions, timers, TextEditingControllers, caches — released in dispose() (widgets) or ref.onDispose (providers). autoDispose scoped session state so it does not survive the screen.
2211. **Measure in PROFILE mode on a real floor device with DevTools.** Debug timings are meaningless (JIT, asserts). Watch the **raster thread** as well as the UI thread — saveLayer/blur/clip cost shows there, not in Dart. Never ship a frame-budget number that was asserted, not measured.
23
24## Narrow the rebuild scope
This is a preview of SKILL.md. Download or install the skill to get the whole thing.
In the file
SKILL.md1,308 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.

≈160
always loaded
The name and description, so the model knows the skill exists and when to reach for it.
2,315
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

2.5k 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, 9.9 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

  • SKILL.md9.9 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.

# Flutter Performance · 2.5k tokens when loaded · macOS, Linux mkdir -p .claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/flutter-performance/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/flutter-performance" ] && { [ ! -e .claude/skills/flutter-performance ] || { mv .claude/skills/flutter-performance "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/flutter-performance" .claude/skills/ && echo "Installed .claude/skills/flutter-performance"
On Windows, or any OS with Node 20+
npx mcprush@latest skill add zakariaf/flutter-performance

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/flutter-performance/ 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/flutter-performance/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/flutter-performance" ] && { [ ! -e ~/.claude/skills/flutter-performance ] || { mv ~/.claude/skills/flutter-performance "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/flutter-performance" ~/.claude/skills/ && echo "Installed ~/.claude/skills/flutter-performance" (macOS, Linux) — or add --global to the npx line. The curl line replaces .claude/skills/flutter-performance/ 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
Referencezakariaf/flutter-performance

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.

Reviews

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