Agent skill

App Control

Launch, configure, drive, screenshot and measure the running NullPlayer app.

Custom licenceAuto-check passedTesting & QA

Install App Control

skills CLI

$ npx skills add ad-repo/nullplayer --skill app-control -a claude-code

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

GitHub CLI

$ gh skill install ad-repo/nullplayer app-control --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/ad-repo/nullplayer.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/app-control .claude/skills/app-control && 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/

Paste into Claude Code

Install the "app-control" agent skill from https://github.com/ad-repo/nullplayer/tree/main/skills/app-control into .claude/skills/app-control/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "app-control", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/ad-repo/nullplayer/tree/main/skills/app-control

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add ad-repo/nullplayer --skill app-control -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install ad-repo/nullplayer app-control --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ad-repo/nullplayer.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/app-control .agents/skills/app-control && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "app-control" agent skill from https://github.com/ad-repo/nullplayer/tree/main/skills/app-control into .agents/skills/app-control/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "app-control", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add ad-repo/nullplayer --skill app-control -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install ad-repo/nullplayer app-control --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ad-repo/nullplayer.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/app-control .cursor/skills/app-control && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "app-control" agent skill from https://github.com/ad-repo/nullplayer/tree/main/skills/app-control into .cursor/skills/app-control/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "app-control", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/ad-repo/nullplayer.git --path skills/app-control

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add ad-repo/nullplayer --skill app-control -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install ad-repo/nullplayer app-control --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ad-repo/nullplayer.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/app-control .gemini/skills/app-control && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "app-control" agent skill from https://github.com/ad-repo/nullplayer/tree/main/skills/app-control into .gemini/skills/app-control/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "app-control", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install ad-repo/nullplayer app-control

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add ad-repo/nullplayer --skill app-control -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/ad-repo/nullplayer.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/app-control .github/skills/app-control && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "app-control" agent skill from https://github.com/ad-repo/nullplayer/tree/main/skills/app-control into .github/skills/app-control/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "app-control", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add ad-repo/nullplayer --skill app-control -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install ad-repo/nullplayer app-control --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ad-repo/nullplayer.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/app-control .opencode/skills/app-control && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "app-control" agent skill from https://github.com/ad-repo/nullplayer/tree/main/skills/app-control into .opencode/skills/app-control/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "app-control", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: app-control
GitHub stars: 158
Token cost: ~9.4k tokens
SKILL.md length: 5,058 words
Files: 17 (incl. scripts)
Skills in repo: 40
Repo updated: Oct 10, 2026
First seen: Oct 7, 2026
Licence: Custom licence

At a glance

Launch, configure, drive, screenshot and measure the running NullPlayer app.

Works in 2 steps: A recipe that builds any other way is a… → There is exactly one defaults domain in…
Asked to run / launch / start the app
SKILL.md covers Rule zero: the app under test…, Routing, Route A — don't launch the GUI and Route B — launch…, plus 5 more sections
Runs Shell, AppleScript, Python and Swift scripts from its folder; calls swift, osascript and git

What it does

App Control is an agent skill from ad-repo/nullplayer. Launch, configure, drive, screenshot and measure the running NullPlayer app. Use when asked to run / launch / start the app, click or drag a control, reproduce a defect on screen, "open skin X", "show me it working", set up a test scenario, capture a window, check that every window opens, stretches and closes, or hand the user a loaded interactive session. Covers every skin family (Classic, Original, Original-Metal, Winamp Modern .wal, Windows Media Player .wmz, Audion faces) and names the canonical test-data…

Its SKILL.md is about 9.4k tokens, which your agent loads only when the skill is triggered. The skill folder holds 19 other files, including scripts (for example `eval/README.md`, `eval/case-01-wmp-elapsed-readout.md` and `eval/ground-truth.md`).

It sits in Testing & QA, covering Test data and fixtures. It works with Swift. The repository describes itself as: nullPlayer is a free open source macOS media player with some unique features.

When your agent uses it

Asked to run / launch / start the app
Reproduce a defect on screen
Show me it working
Set up a test scenario

Example prompts

“open skin X”
“show me it working”
“/app-control”

Requirements

Python 3
A Bash shell

Workflow steps

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

A recipe that builds any other way is a bug in the recipe. Release exists only for a deliberate
There is exactly one defaults domain in this skill: NullPlayer. com.nullplayer.app is

What it can do on your machine

Read from SKILL.md and the folder at commit 3d87ce1. 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
Ships 10 files in scripts/ (Shell, AppleScript, Python and Swift), which the agent can run.
Shell commands in SKILL.md call:
- swift
- osascript
- git
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md. Its commands use git, which can reach the network depending on how they are called.
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

App Control loads about 9.4k tokens when it runs. Until then it costs about 134 tokens; SKILL.md has 5,058 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~134
When it runs · the whole SKILL.md, loaded when a task matches: ~9.4k

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); the scripts in this folder are not scanned.

SKILL.md

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 5,058 words (~9,445 tokens).

“skills/app-control/scripts/launch.sh is the launch command (Route B); it runs ./scripts/kill_build_run.sh --debug, which is the build-and-run command for a launch with no skin to pin. Not swift build, not Xcode, not a release build.”

— opening of SKILL.md by ad-repo, Custom licence

name: app-control

Outline of SKILL.md

Controlling the app
Rule zero: the app under test is the local debug build, always
Routing
Route A — don't launch the GUI
Route B — launch preconfigured, don't click
Route C — drive it yourself
Route D — hand the user a loaded session
Route E — measure
Playback snapshot — read audio and cast state from the running app
Skin window-size isolation (user-level regression test)
Skin family switching matrix
Window open / stretch / close matrix
Window census
Test data
Debugging a live defect

Read the full SKILL.md on GitHub

Files

SKILL.md and 16 other files (scripts) in skills/app-control of ad-repo/nullplayer.

SKILL.md
eval/README.md
eval/case-01-wmp-elapsed-readout.md
eval/ground-truth.md
eval/rubric.md
reference/launch-recipes.md
reference/test-data.md
scripts/build.sh
scripts/launch.sh
scripts/menu.applescript
scripts/playback-snapshot.sh
scripts/size-isolation-test.sh
scripts/skin-mode-switch-test.sh
scripts/skin-pick-matrix.py
scripts/window-census.sh
scripts/window-interaction-matrix.sh
scripts/winhelper.swift

Open the folder on GitHubat commit 3d87ce1

Compare with similar skills

App Control 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.

App Control compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
App Control this skillad-repo/nullplayer	158	—	~9.4k	Automated safety check: Pass	Custom licence	today
Jest Testing PatternsChrisWiles/claude-code-showcase	6.1k	7 repos	~1.5k	Automated safety check: Pass	None	9 mo ago
Java SDK E2E Test with Replay Snapshotgithub/copilot-sdk	11k	—	~1.8k	Automated safety check: Pass	MIT	today
source-mssql E2E Test Harnessairbytehq/airbyte	22k	—	~4.4k	Automated safety check: Pass	Custom licence	today
RTK Filter TDD in Rustrtk-ai/rtk	83k	—	~1.9k	Automated safety check: Notes	Apache-2.0	today
OpenLogi Device Fixture ContributionAprilNEA/OpenLogi	23k	—	~1.2k	Automated safety check: Pass	Apache-2.0	today

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Questions about App Control

What does App Control do?

Launch, configure, drive, screenshot and measure the running NullPlayer app. App Control is an agent skill from ad-repo/nullplayer. Launch, configure, drive, screenshot and measure the running NullPlayer app.

When should I use App Control?

App Control fits situations like: asked to run / launch / start the app; reproduce a defect on screen; show me it working; set up a test scenario.

How do I install App Control in Claude Code?

Run `npx skills add ad-repo/nullplayer --skill app-control -a claude-code`. Or copy the skill folder (skills/app-control in ad-repo/nullplayer) into .claude/skills/app-control in your project. Claude Code loads it when a task matches its description.

How do I install App Control in Codex?

Run `npx skills add ad-repo/nullplayer --skill app-control -a codex`. Or copy the skill folder (skills/app-control in ad-repo/nullplayer) into .agents/skills/app-control in your project. Codex loads it when a task matches its description.

Can I use App Control 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 ad-repo/nullplayer --skill app-control -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/app-control, .gemini/skills/app-control, .github/skills/app-control and .opencode/skills/app-control in your project.

What does App Control need to run?

Going by SKILL.md and its folder, App Control needs a shell, AppleScript, Python and Swift for the scripts in its folder and the command-line tools its instructions call (swift, osascript and git). Our summary lists: Python 3; A Bash shell.

Does App Control access the network?

SKILL.md contains no URLs. Its commands use git, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is App Control 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. The check reads SKILL.md only: the scripts in the folder are not scanned, so read them before running anything.

What licence does App Control use?

App Control has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does App Control use?

About 9.4k tokens (SKILL.md is roughly 38k 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 App Control?

Skills that share tags, products or a category with App Control: Jest Testing Patterns (ChrisWiles/claude-code-showcase, 6.1k stars), Java SDK E2E Test with Replay Snapshot (github/copilot-sdk, 11k stars), source-mssql E2E Test Harness (airbytehq/airbyte, 22k stars) and RTK Filter TDD in Rust (rtk-ai/rtk, 83k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains App Control?

ad-repo (a GitHub user) maintains it in ad-repo/nullplayer, which has 158 GitHub stars. The repository holds 40 skills in this directory. The repository was last updated on October 10, 2026.

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

App Control

Install App Control

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Files

Compare with similar skills

Similar skills

Jest Testing Patterns

Java SDK E2E Test with Replay Snapshot

source-mssql E2E Test Harness

RTK Filter TDD in Rust

OpenLogi Device Fixture Contribution

Airbyte source-mysql E2E Tests

More from ad-repo/nullplayer

Skin Screenshots

Vis Classic Guide

Chromecast Casting

Emby Integration

Live UI Testing

Metal Gotchas

Questions about App Control

Install App Control

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Files

Compare with similar skills

Similar skills

More from ad-repo/nullplayer

Related

Questions about App Control