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Agent skill

Aster UI Demo

by Zfinix in Zfinix/aster

How to demo UI work the way Claude does it, never with throwaway HTML mockups.

Apache-2.0Auto-check passedTesting & QA

Install Aster UI Demo

skills CLI
$ npx skills add Zfinix/aster --skill aster-ui-demo -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install Zfinix/aster aster-ui-demo --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/Zfinix/aster.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/aster-ui-demo .claude/skills/aster-ui-demo && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
aster-ui-demo
GitHub stars
118
Token cost
~670 tokens
SKILL.md length
357 words
Files
1
Skills in repo
19
Repo updated
First seen
Licence
Apache-2.0

At a glance

How to demo UI work the way Claude does it, never with throwaway HTML mockups.

  • Works in 5 steps: Build it for real. Implement the change… → Serve it in the browser harness. From… → Click through it yourself first. Use… → …
  • The user asks for a demo
  • SKILL.md covers The workflow, Reporting and Why not mockups
  • Calls bun, bash and make

What it does

Aster UI Demo is an agent skill from Zfinix/aster. How to demo UI work the way Claude does it, never with throwaway HTML mockups. Build the change in the real webview, verify it in the browser harness, open the live dev server for the user to click through, and run the real test suites. Use when the user asks for a demo, a preview, or "let me see" any UI change in the desktop or VS Code surfaces.

Its SKILL.md is about 670 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Testing & QA, covering Test generation. It works with Visual Studio Code. The repository describes itself as: An open-source agent harness for software work. The licence is Apache-2.0.

When your agent uses it

  • The user asks for a demo
  • Let me see any UI change in the desktop
  • VS Code surfaces

Example prompts

  • “let me see”
  • “/aster-ui-demo”

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

  1. Build it for real. Implement the change in the actual frontend source,
  2. Serve it in the browser harness. From editors/vscode/, run
  3. Click through it yourself first. Use browser automation to exercise the
  4. Open it for the user. Use open_preview on the harness URL so they can
  5. Run the real checks before calling it done: bun run test (vitest) in

What it can do on your machine

Read from SKILL.md and the folder at commit f77a5b4. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Shell commands in SKILL.md call:

    • bun
    • bash
    • make
    • cargo

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Aster UI Demo loads about 670 tokens when it runs. Until then it costs about 91 tokens; SKILL.md has 357 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~91
When it runs · the whole SKILL.md, loaded when a task matches
~670

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from Zfinix/aster at commit f77a5b4, republished under its Apache-2.0 licence (© Zfinix). 357 words, ~670 tokens.

Download SKILL.mdSave it as .claude/skills/aster-ui-demo/SKILL.md (or your agent's skills folder).
name
aster-ui-demo
description
How to demo UI work the way Claude does it, never with throwaway HTML mockups. Build the change in the real webview, verify it in the browser harness, open the live dev server for the user to click through, and run the real test suites. Use when the user asks for a demo, a preview, or "let me see" any UI change in the desktop or VS Code surfaces.

Demo UI work in the real surface

Never build a standalone HTML mockup to show a UI idea. Users judge UI by clicking the real product, and a mockup cannot answer the only questions that matter: does it work, does it match the surrounding design, does it survive real data.

The workflow

  1. Build it for real. Implement the change in the actual frontend source, even when the user only asked to "see it first". For this repo that means editors/vscode/webview/ (shared webview used by both the VS Code panel and the browser harness) or desktop/ for Tauri surfaces.

  2. Serve it in the browser harness. From editors/vscode/, run bun run dev:web (builds the webview, then runs out/devhost/main.js, a real browser-runnable host with a stubbed vscode API). The devhost is a long-lived server: never run it directly through run_command, or the tool hangs until the process is killed. Fire and forget through a shell:

    sh
    bash -lc "cd editors/vscode && bun run dev:web > /tmp/devhost.log 2>&1 &"

    Note the port (default 4327). If the port does not come up, read /tmp/devhost.log in a later round instead of chaining a wait onto the start command.

  3. Click through it yourself first. Use browser automation to exercise the feature before the user sees it: open the panel, trigger the feature, resize narrow (300px) to check layout. Fix what breaks.

  4. Open it for the user. Use open_preview on the harness URL so they can click through the running app. State plainly that it is the real surface, running in a browser host.

  5. Run the real checks before calling it done: bun run test (vitest) in editors/vscode/, and make check or scoped cargo test -p aster-cli for Rust changes.

Show full SKILL.md (83 more words)Show less

Reporting

Reference real files with line numbers, describe behavior the user can trigger by clicking, and note anything the browser harness cannot reproduce (native menus, real extension API calls) so the user knows what still needs testing in the actual editor.

Why not mockups

A mockup gets one reaction ("looks fine") and then the work is thrown away. The real build gets the same reaction plus every real bug found before the feature ships. The mockup path only wastes the turn it saves.

© Zfinix, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/aster-ui-demo of Zfinix/aster.

Open the folder on GitHubat commit f77a5b4

Compare with similar skills

Aster UI Demo next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Aster UI Demo compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Aster UI Demo this skillZfinix/aster118—~670Automated safety check: PassApache-2.0
Write and Verify Playwright Testsappsmithorg/appsmith41k—~2.9kAutomated safety check: NotesApache-2.0
Adk Verify Snippetsgoogle/adk-python22k—~1.4kAutomated safety check: PassApache-2.0
Engine E2Ewix/react-native-navigation13k—~1.1kAutomated safety check: PassMIT
Hermetic Python Unit TestsdimensionalOS/dimos4.6k—~1.4kAutomated safety check: PassCustom licence
Emcaklofas/kicad-happy1.4k1 repos~2.8kAutomated safety check: PassMIT

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All 19 skills in this repo

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  • Aster Config

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    Reference for aster.yaml, covering review models, analyzers, focus areas, include/exclude globs, minconfidence, and the permissions block that gates edits.

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  • Aster Fix Workflow

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Works with

Categories

Questions about Aster UI Demo

What does Aster UI Demo do?

How to demo UI work the way Claude does it, never with throwaway HTML mockups. Aster UI Demo is an agent skill from Zfinix/aster. How to demo UI work the way Claude does it, never with throwaway HTML mockups.

When should I use Aster UI Demo?

Aster UI Demo fits situations like: the user asks for a demo; let me see any UI change in the desktop; VS Code surfaces.

How do I install Aster UI Demo in Claude Code?

Run `npx skills add Zfinix/aster --skill aster-ui-demo -a claude-code`. Or copy the skill folder (skills/aster-ui-demo in Zfinix/aster) into .claude/skills/aster-ui-demo in your project. Claude Code loads it when a task matches its description.

How do I install Aster UI Demo in Codex?

Run `npx skills add Zfinix/aster --skill aster-ui-demo -a codex`. Or copy the skill folder (skills/aster-ui-demo in Zfinix/aster) into .agents/skills/aster-ui-demo in your project. Codex loads it when a task matches its description.

Can I use Aster UI Demo in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add Zfinix/aster --skill aster-ui-demo -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/aster-ui-demo, .gemini/skills/aster-ui-demo, .github/skills/aster-ui-demo and .opencode/skills/aster-ui-demo in your project.

What does Aster UI Demo need to run?

Going by SKILL.md and its folder, Aster UI Demo needs the command-line tools its instructions call (bun, bash, make and cargo).

Does Aster UI Demo access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Aster UI Demo safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Aster UI Demo use?

Aster UI Demo is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Aster UI Demo use?

About 670 tokens (SKILL.md is roughly 2.7k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Aster UI Demo?

Skills that share tags, products or a category with Aster UI Demo: Write and Verify Playwright Tests (appsmithorg/appsmith, 41k stars), Adk Verify Snippets (google/adk-python, 22k stars), Engine E2E (wix/react-native-navigation, 13k stars) and Hermetic Python Unit Tests (dimensionalOS/dimos, 4.6k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Aster UI Demo?

Zfinix (a GitHub user) maintains it in Zfinix/aster, which has 118 GitHub stars. The repository holds 19 skills in this directory. The repository was last updated on October 9, 2026.

Source: Zfinix/aster on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.