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.
npx agentmods add skills/flutter/agent-plugins/flutter-add-widget-previewnpx skills add flutter/agent-plugins --skill flutter-add-widget-previewgit clone --depth 1 https://github.com/flutter/agent-pluginsWhat 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 | $0.00036 | $0.01324 |
| Opus 5 | $0.00018 | $0.00662 |
| Sonnet 5 | $0.00007 | $0.00265 |
| Haiku 4.5 | $0.00004 | $0.00132 |
Grade A, and why
flutter-add-widget-preview 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 2d 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.
How it starts
The opening of the file, as written. The whole thing — 146 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Previewing Flutter Widgets
Contents
Preview Guidelines
Use the Flutter Widget Previewer to render widgets in real-time, isolated from the full application context.
- Target Elements: Apply the
@Previewannotation to top-level functions, static methods within a class, or public widget constructors/factories that have no required arguments and return aWidgetorWidgetBuilder. - Imports: Always import
package:flutter/widget_previews.dartto access the preview annotations. - Custom Annotations: Extend the
Previewclass to create custom annotations that inject common properties (e.g., themes, wrappers) across multiple widgets. - Multiple Configurations: Apply multiple
@Previewannotations to a single target to generate multiple preview instances. Alternatively, extendMultiPreviewto encapsulate common multi-preview configurations. - Runtime Transformations: Override the
transform()method in customPrevieworMultiPreviewclasses to modify preview configurations dynamically at runtime (e.g., generating names based on dynamic values, which is impossible in aconstcontext).
Handling Limitations
Adhere to the following constraints when authoring previewable widgets, as the Widget Previewer runs in a web environment:
- No Native APIs: Do not use native plugins or APIs from
dart:ioordart:ffi. Widgets with transitive dependencies ondart:ioordart:ffiwill throw exceptions upon invocation. Use conditional imports to mock or bypass these in preview mode. - Asset Paths: Use package-based paths for assets loaded via
dart:uifromAssetAPIs (e.g.,packages/my_package_name/assets/my_image.pnginstead ofassets/my_image.png). - Public Callbacks: Ensure all callback arguments provided to preview annotations are public and constant to satisfy code generation requirements.
- Constraints: Apply explicit constraints using the
sizeparameter in the@Previewannotation if your widget is unconstrained, as the previewer defaults to constraining them to approximately half the viewport.
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.
- 2d ago First seen · 146 lines · 36 tokens per session scan A 88cfeb7084e7
flutter-add-widget-preview is a skill published in the GitHub repository flutter/agent-plugins (2,895 stars, last pushed 4d ago), licensed BSD-3-Clause. It adds 36 tokens to every session and 1,324 once invoked, about $0.0002 per session on Opus 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 2026-08-30.
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