What is preview-widget?

A tool for viewing one Flutter widget by itself in Flutter's Widget Previewer. Flutter is a framework for building app interfaces; the preview uses the project's real theme and data providers.

Use it to preview and screenshot one widget while refining its layout, styling, and behavior in a Flutter project.

It lets you adjust a single component without starting the whole app or following a complete user flow. This makes small visual changes and light, dark, or tablet variants easier to compare.

preview-widget — Skill for Claude Code and Codex by ChunkyTofuStudios

Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo

git clone --depth 1 https://github.com/ChunkyTofuStudios/flutter-skills

agentmods

npx agentmods add skills/chunkytofustudios/flutter-skills/preview-widget

Made for: Claude Code, Codex.

Its marketplace also offers this one on its own, as the plugin preview-widget — /plugin install preview-widget after adding the marketplace above.

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/chunkytofustudios/flutter-skills/preview-widget/github.svg)](https://agentmods.dev/skills/chunkytofustudios/flutter-skills/preview-widget)

Your own site

<a href="https://agentmods.dev/skills/chunkytofustudios/flutter-skills/preview-widget"><img src="https://agentmods.dev/badge/skills/chunkytofustudios/flutter-skills/preview-widget/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/chunkytofustudios/flutter-skills/preview-widget"><img src="https://agentmods.dev/badge/skills/chunkytofustudios/flutter-skills/preview-widget.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 210 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,953 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00210	$0.02953
Opus 5.5	$0.00084	$0.01181
Sonnet 5.5	$0.00042	$0.00591
Haiku 4.5	$0.00021	$0.00295

Measured 1mo ago against content hash 23b6c47ac3c0, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

preview-widget 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 1mo ago.

The scan reads SKILL.md. This mod also ships 5 executable files (scripts/check_preview_support.sh, scripts/list_previews.sh, scripts/screenshot_preview.sh, …), 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.

skills/preview-widget/SKILL.md · 184 lines

How it starts

The opening of the file, as written. The whole thing — 184 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Render a single widget in Flutter's Widget Previewer so you and the human can iterate on it — design tweaks, light/dark variants, tablet sizing — without booting the full app. The agent screenshots the live preview headlessly; the human optionally opens the same localhost URL in their own Chrome to follow along.

When to use this

All three must hold — if any is false, this skill is the wrong tool:

The project is a Flutter project (pubspec.yaml at the cwd, lib/ exists).
Flutter ≥ 3.35 is on PATH (or via fvm flutter). The previewer is experimental on stable but stable enough to design against; older Flutters don't have it.
The user wants to iterate on a single widget, not a full screen or end-to-end flow. Full-screen visual work is what design-polish + android-emulator is for.

Setup (caller's machine)

Requirement	How to satisfy
Flutter ≥ 3.35	Run `bash scripts/check_preview_support.sh` — fails loudly with an upgrade hint if too old. Override the Flutter binary with `FLUTTER_BIN=…` (default: `flutter`, falls back to `fvm flutter`).
Google Chrome / Chromium	Used headlessly by `screenshot_preview.sh` to capture previews. macOS picks up `/Applications/Google Chrome.app` automatically; on Linux any of `google-chrome`, `chromium`, `chromium-browser` on PATH works. Override with `CHROME_BIN=/path/to/chrome`.
`bash` 3.2+ (macOS default), `awk`, `grep`, `find`	Standard. No Python or Node needed.

There's no per-machine auth, account, or token — everything runs on localhost.

Bundled scripts

scripts/check_preview_support.sh — verifies Flutter ≥ 3.35 and prints the resolved binary + version. Exit 0 = ready, exit 1 = version too old, exit 127 = no Flutter found.
scripts/start_preview.sh — launches flutter widget-preview start in the background, parses the URL out of its log, and writes a small JSON state file. Idempotent: re-runs return the existing URL. --stop tears the server down. Default state dir: ./.preview-widget/ (override with PREVIEW_WIDGET_STATE_DIR).
scripts/screenshot_preview.sh — headless-Chrome screenshot of the running previewer. Flags: --out <path>, --size WxH (default 1600x2400), --wait <ms> (virtual-time budget, default 10000), --url <url> (override the state file). Prints the absolute output path on stdout.
scripts/list_previews.sh — greps lib/ for @Preview(...), @<Custom>Preview(...), and extends (Multi)?Preview definitions so you don't re-add what's already there.

Read the full file on GitHub · 184 lines

Files

What ships with it

17 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.

1mo ago First seen · 184 lines · 210 tokens per session scan A 23b6c47ac3c0

Subscribe to this mod's changes

preview-widget is a skill published in the GitHub repository ChunkyTofuStudios/flutter-skills (5 stars, last pushed 5mo ago), licensed MIT. It adds 210 tokens to every session and 2,953 once invoked, about $0.0008 per session on Opus 5.5. 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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