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Agent skill

App Extensions

by gustavscirulis in gustavscirulis/snapgrid

Generates app extension infrastructure for Share Extensions, Action Extensions, Keyboard Extensions, and Safari Web Extensions with data sharing via App Groups.

Custom licenceAuto-check: notes

Install App Extensions

skills CLI
$ npx skills add gustavscirulis/snapgrid --skill app-extensions -a claude-code

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

GitHub CLI
$ gh skill install gustavscirulis/snapgrid app-extensions --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/gustavscirulis/snapgrid.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.claude/skills/skills/generators/app-extensions .claude/skills/app-extensions && 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
app-extensions
GitHub stars
116
Used in
1 other repo
Token cost
~2.5k tokens
SKILL.md length
955 words
Files
2
Skills in repo
118
Repo updated
First seen
Licence
Custom licence

At a glance

Generates app extension infrastructure for Share Extensions, Action Extensions, Keyboard Extensions, and Safari Web Extensions with data sharing via App Groups.

  • Works in 7 steps: Project Context Detection → Existing Extension Detection → App Groups Detection → …
  • User wants to add a share extension
  • SKILL.md covers When This Skill Activates, Pre-Generation Checks, Configuration Questions and Generation Process, plus 4 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

App Extensions is an agent skill from gustavscirulis/snapgrid. Generates app extension infrastructure for Share Extensions, Action Extensions, Keyboard Extensions, and Safari Web Extensions with data sharing via App Groups. Use when user wants to add a share extension, action extension, keyboard extension, Safari web extension, or any app extension type.

Its SKILL.md is about 2.5k tokens, which your agent loads only when the skill is triggered. The skill folder holds 1 other file (for example `templates.md`).

The repository describes itself as: SnapGrid is an open-source Mac app for collecting, organizing, and analyzing UI screenshots. It uses AI to automatically detect UI components and patterns, making it a powerful…

When your agent uses it

  • User wants to add a share extension
  • Action extension
  • Keyboard extension
  • Safari web extension

Example prompts

  • “Use the app-extensions skill to generate app extension infrastructure for Share Extensions, Action Extensions, Keyboard Extensions, and Safari Web…”
  • “/app-extensions”

Requirements

  • Pre-approved tools (allowed-tools): Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion

Workflow steps

7 steps, taken from the step headings in SKILL.md.

  1. Project Context Detection
  2. Existing Extension Detection
  3. App Groups Detection
  4. Read Templates
  5. Create Extension Files
  6. Create Shared Infrastructure
  7. Determine File Location

What it can do on your machine

Read from SKILL.md and the folder at commit eb7eaf4. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves these tools, so the agent can use them without asking each time:

    • Read
    • Write
    • Edit
    • Glob
    • Grep
    • Bash
    • AskUserQuestion

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are swift).

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

  • Network

    Links to these hosts (documentation or services it may open):

    • developer.apple.com

    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 Extensions loads about 2.5k tokens when it runs. Until then it costs about 77 tokens; SKILL.md has 955 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~77
When it runs · the whole SKILL.md, loaded when a task matches
~2.5k

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: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

  • NotePre-approves every shell command (allowed-tools: Bash)SKILL.md
    allowed-tools: Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion

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

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 955 words (~2,483 tokens).

“Generate production app extension infrastructure -- Share Extensions for receiving content from other apps, Action Extensions for manipulating content in-place, Keyboard Extensions for custom input, and Safari Web Extensions for browser integration. Includes App Group data sharing between the host…”

— opening of SKILL.md by gustavscirulis, Custom licence
name
app-extensions
allowed-tools
Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion

Read the full SKILL.md on GitHub

Files

SKILL.md and 1 other file in .claude/skills/skills/generators/app-extensions of gustavscirulis/snapgrid.

  • SKILL.md
  • templates.md

Open the folder on GitHubat commit eb7eaf4

Used in 1 other repository

We found 1 copy of this SKILL.md (exact, near-identical or edited) in other folders, from 1 other GitHub owner. This page covers the copy in gustavscirulis/snapgrid, which our catalogue first saw on October 7, 2026.

Compare with similar skills

App Extensions 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 Extensions compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
App Extensions this skillgustavscirulis/snapgrid1161 repos~2.5kAutomated safety check: NotesCustom licence
ShareClickHouse/ClickHouse50k—~558Automated safety check: NotesApache-2.0
Generatealirezarezvani/claude-skills28k1 repos~1.1kAutomated safety check: PassMIT
Fal Generatenexu-io/open-design100k—~306Automated safety check: PassApache-2.0
Video Generationbytedance/deer-flow84k3 repos~1.4kAutomated safety check: PassMIT
Image Generationonyx-dot-app/onyx32k1 repos~1.7kAutomated safety check: PassCustom licence

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  • Alarmkit

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  • Analytics Interpretation

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  • Analytics Setup

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  • Announcement Banner

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Questions about App Extensions

What does App Extensions do?

Generates app extension infrastructure for Share Extensions, Action Extensions, Keyboard Extensions, and Safari Web Extensions with data sharing via App Groups. App Extensions is an agent skill from gustavscirulis/snapgrid. Generates app extension infrastructure for Share Extensions, Action Extensions, Keyboard Extensions, and Safari Web Extensions with data sharing via App Groups.

When should I use App Extensions?

App Extensions fits situations like: user wants to add a share extension; action extension; keyboard extension; safari web extension.

How do I install App Extensions in Claude Code?

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

How do I install App Extensions in Codex?

Run `npx skills add gustavscirulis/snapgrid --skill app-extensions -a codex`. Or copy the skill folder (.claude/skills/skills/generators/app-extensions in gustavscirulis/snapgrid) into .agents/skills/app-extensions in your project. Codex loads it when a task matches its description.

Can I use App Extensions 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 gustavscirulis/snapgrid --skill app-extensions -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-extensions, .gemini/skills/app-extensions, .github/skills/app-extensions and .opencode/skills/app-extensions in your project.

What does App Extensions need to run?

SKILL.md names no scripts, command-line tools or credentials: App Extensions is instructions for the agent only. Its frontmatter pre-approves these tools: Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion.

Does App Extensions access the network?

SKILL.md names 1 domain. As links in the text: developer.apple.com. This is read from the text; nothing was executed.

Is App Extensions safe to install?

Our automated static check of SKILL.md found notes only (pre-approves every shell command (allowed-tools: bash)), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does App Extensions use?

App Extensions 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 Extensions use?

About 2.5k tokens (SKILL.md is roughly 9.9k 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 Extensions?

Skills that share tags, products or a category with App Extensions: Share (ClickHouse/ClickHouse, 50k stars), Generate (alirezarezvani/claude-skills, 28k stars), Fal Generate (nexu-io/open-design, 100k stars) and Video Generation (bytedance/deer-flow, 84k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains App Extensions?

gustavscirulis (a GitHub user) maintains it in gustavscirulis/snapgrid, which has 116 GitHub stars. The repository holds 118 skills in this directory. The repository was last updated on April 30, 2026.

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