muxy-extension

muxy-extension is a skill for Claude Code, Codex from tofunori/atelier-studio. It costs 77 tokens per session (5,887 once invoked), scanned A, original, MIT.

A guide for building Muxy extensions, which are small npm and Vite web projects that add a panel or other feature to the Muxy app.

In plain words
What is it for?
Use it when developing, testing, or publishing a Muxy extension, especially when configuring package.json, Vite builds, themes, permissions, or the window.muxy API.
Why use it?
It explains the required project files, manifest placement, build output, sizing, theming, and app surface so an extension loads and looks like part of Muxy.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions Claude Code; installed under .agents/ (shared by several agents); mentions Codex.

Good fit Use it when developing, testing, or publishing a Muxy extension, especially when configuring package.json, Vite builds, themes, permissions, or the window.muxy API.

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Install with agentmods
npx agentmods add skills/tofunori/atelier-studio/muxy-extension
Install

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.

Any agent
npx skills add tofunori/atelier-studio --skill muxy-extension
Clone the repo
git clone --depth 1 https://github.com/tofunori/atelier-studio

Made for: Claude Code, Codex.

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.

agentmods badge for muxy-extension

README.md
[![agentmods](https://agentmods.dev/badge/skills/tofunori/atelier-studio/muxy-extension/github.svg)](https://agentmods.dev/skills/tofunori/atelier-studio/muxy-extension)
Your own site
<a href="https://agentmods.dev/skills/tofunori/atelier-studio/muxy-extension"><img src="https://agentmods.dev/badge/skills/tofunori/atelier-studio/muxy-extension/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.

agentmods 80×15 button for muxy-extension

Your own site · 80×15
<a href="https://agentmods.dev/skills/tofunori/atelier-studio/muxy-extension"><img src="https://agentmods.dev/badge/skills/tofunori/atelier-studio/muxy-extension.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 77 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,887 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00077 $0.05887
Opus 5 $0.00039 $0.02943
Sonnet 5 $0.00015 $0.01177
Haiku 4.5 $0.00008 $0.00589

Measured 10d ago against content hash c4ad9c5e03c2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

muxy-extension scanned grade A with 1 finding 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 10d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

- **Use `muxy.http.fetch` to call external APIs from a tab/panel/popover** instead of the webview's `fetch()` — the request goes out via native code, so it is **not CORS-blocked**, and a panel needs no `background.js` (n
gallery/cmux-gallery/.agents/skills/muxy-extension/SKILL.md · 124 lines

How it starts

The opening of the file, as written. The whole thing — 124 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Muxy Extension Guide

A Muxy extension is an npm + Vite project: source under src/, an entry HTML that vite build emits into dist/, and Muxy reads dist/ when present (otherwise the project folder). The manifest is the "muxy" object in package.json. There is no fixed folder layout — every entry/background/icon path is an arbitrary relative path inside the build output (the vanilla starter kit emits its panel to panel/index.html); package.json and dist/ are the only names Muxy fixes. During development you don't copy into the config folder — Load Unpacked in the Extensions modal points Muxy at any folder (your git checkout is the install).

The build script must copy package.json into dist/. The publish pipeline ships only dist/, and the app reads the manifest from the install root — so the manifest has to be inside the build output. vite build alone emits your entry/asset paths but not the manifest, so use "build": "vite build && node scripts/copy-manifest.mjs" where copy-manifest.mjs copies package.json into dist/. Easy to miss because Load Unpacked falls back to the root package.json in dev, so it loads locally but fails validation/install when published. The vanilla starter kit already wires this up.

This skill is the guidance layer — how an extension should look and behave. For the API and manifest mechanics (every field, the permission strings, the full window.muxy surface, events, scripts), read the reference docs. Start from the LLM-friendly index, which lists every page and links to its raw Markdown source:

https://muxy.app/llms.txt

Append /plain to any docs URL for the raw Markdown of that page (e.g. https://muxy.app/docs/extensions/manifest/plain).

The goal of everything below: an extension should be indistinguishable from a native Muxy surface. Match the theme and match the scale, and it will be.

Pick the right surface

  • Showing something to the user → a UI page (tab, panel, or popover). Page scripts get the full window.muxy API.
  • A persistent, full-height navigation or control surface that replaces the built-in left sidebar → a sidebar (one per extension; the user selects it in Settings → Sidebar). It fills the entire region — the project list and the footer — so own your own navigation. Same window.muxy API and theme variables as a panel.
  • Reacting durably to events, coordinating multiple webviews, or running shell commands headlessly → a background.js script. It can also call muxy.tabs.open to show a result in the active workspace. Most extensions don't need one.
  • One-shot logic from the palette → a runScript command, not a hidden tab. Its muxy.* calls are synchronous (return values directly — no await). It has tabs/panes/projects/worktrees/browser/agents/files/git/exec/dialog/modal/topbar/statusbar/notifications, but not http, events, remote, panels, or popover. It can open a modal and act on the choice inline — no page or background listener needed.

Read the full file on GitHub · 124 lines

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.

  1. 10d ago First seen · 124 lines · 77 tokens per session scan A c4ad9c5e03c2

Subscribe to this mod's changes

muxy-extension is a skill published in the GitHub repository tofunori/atelier-studio (2 stars, last pushed today), licensed MIT. It adds 77 tokens to every session and 5,887 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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