Cross Origin Isolation

CommunityPopular

thedaviddias

cross-origin-isolation

Use when reviewing security-sensitive web apps, SharedArrayBuffer usage, worker-heavy apps, editors, or measurement features that require cross-origin isolation. Check both headers and real browser behavior.

Overview

Publisher	thedaviddias
Repository	`Front-End-Checklist`
Skill name	`cross-origin-isolation`
Stars	74.4K
Forks	6.8K
Bundled files	1
License	MIT
Links	Skill source Repository Homepage

Markdown instructions
A SKILL.md file the model loads on demand, so it only costs tokens when a request actually matches.
Works with any LLM
AI skills are plain Markdown, not provider-specific code, so this works with GPT, Claude, Gemini, Grok, or a local model.
1 bundled files
Scripts, templates, and references the model can read while it works. Files are read-only and never executed.
Open source
Published by thedaviddias on GitHub. Read the source before you install it.

Installation

Install the Cross Origin Isolation AI skill in TypingMind to use it with any LLM, or drop it into another agent that reads SKILL.md.

Install in TypingMind

TypingMind installs a skill straight from its GitHub folder — it reads SKILL.md, bundles the resource files, and stores the result locally.

Open the app and go to Plugins → Skills.
Choose "Install from GitHub".
Paste the skill folder URL below and confirm.
https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/cross-origin-isolation
Enable the skill in any chat where you want it available.

Store

Installed

Skills

Add skills

Import one or more skills from a public GitHub folder or a local .skill or .zip archive, or SKILL.md file.

From GitHub URLFrom .skill, .zip, or SKILL.md

GitHub repo or folder

https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/cross-origin-isolation

Points to a single skill folder, or any folder that contains multiple skills. Public repos only.

CancelContinue

Plugins → Skills → Add skill → From GitHub URL, then paste the folder URL and press Continue.

Install in another agent

Any agent that reads the Agent Skills format can use this skill — copy the folder into that agent's skills directory.

Claude Code — .claude/skills

git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git /tmp/Front-End-Checklist
mkdir -p .claude/skills
cp -r /tmp/Front-End-Checklist/skills/cross-origin-isolation .claude/skills/cross-origin-isolation

Restart Claude Code after copying so it picks up the new skill.

Use it in TypingMind

Enable Cross Origin Isolation in any TypingMind chat and the model takes it from there. Its name and description sit in the system prompt, and the moment a request matches, the model loads the full instructions itself — you never invoke it by hand, and it costs no tokens until it is actually used.

The model loads Cross Origin Isolation on its own as soon as a request matches it.

Works with any AI model

AI skills are plain Markdown instructions rather than provider-specific code, so Cross Origin Isolation is not tied to the model it was written for. Install it once in TypingMind and use it with GPT-5, Claude, Gemini, Grok, DeepSeek, Mistral, Llama, or a local model you run yourself — all on your own API keys.

Loaded only when it is needed
The system prompt carries just the name and description. The instructions are fetched on the first matching request, so an idle skill costs nothing.
Switch models mid-chat
Because the skill is instructions rather than code, changing model does not break it — the next model reads the same SKILL.md.

Skill instructions

This is the SKILL.md content the model loads. Read it before installing — a skill is instructions your model will follow.

Use COOP, COEP, and CORP for cross-origin isolation when needed

Cross-origin isolation reduces opener-based attacks and XS-Leak risk, and it is required for powerful browser features such as SharedArrayBuffer in modern browsers. It also breaks integrations if deployed carelessly, so it needs a deliberate rollout rather than a copy-pasted header block.

Quick Reference

Use Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy together when you need cross-origin isolation
Audit every cross-origin script, iframe, image, worker, and font before enforcing COEP
Serve embeddable resources with CORS or Cross-Origin-Resource-Policy as appropriate
Verify self.crossOriginIsolated === true before depending on isolated-only features

Check

Review security headers and embedded resources for cross-origin isolation. Check whether the app needs COOP/COEP, whether resources are compatible with COEP, and whether the runtime actually becomes crossOriginIsolated.

Fix

Add COOP and COEP only after auditing dependencies, ensure subresources use CORP or CORS as required, and verify the final document becomes crossOriginIsolated in the browser.

Explain

Explain how COOP, COEP, and CORP work together, what they protect against, and why third-party embeds often block a successful rollout.

Code Review

Review server headers, third-party integrations, popups, workers, and asset responses related to Use COOP, COEP, and CORP for cross-origin isolation when needed. Flag exact responses or integrations that would block isolation or break once isolation is enforced.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/rules/security/cross-origin-isolation

Bundled files

The model reads these on demand while the skill is loaded. They are exposed as readable files and are never executed.

references/rule.md4 KB

Frequently asked questions

What does the Cross Origin Isolation AI skill do?

Why use Cross Origin Isolation on TypingMind?

Because you install it once and use it with any model. Cross Origin Isolation is plain Markdown rather than provider-specific code, so the same skill runs on GPT-5, Claude, Gemini, Grok, or a local model — and you can switch model mid-chat without it breaking. TypingMind runs on your own API keys, so you pay providers directly instead of a per-seat subscription, and your skills and chats stay in your own storage.

How do I install Cross Origin Isolation in TypingMind?

Open Plugins → Skills → Install from GitHub in TypingMind and paste https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/cross-origin-isolation. TypingMind reads its SKILL.md and bundles its files and installs it as a skill you can enable per chat.

Which AI models can use Cross Origin Isolation?

Any model you connect in TypingMind. AI skills are plain Markdown instructions rather than provider-specific code, so GPT, Claude, Gemini, Grok, and local models can all load this skill when a request matches it.

How many AI models can I use with Cross Origin Isolation?

As many as you like. As long as a model supports skills, you can use Cross Origin Isolation with it — GPT, Claude, Gemini, Grok, DeepSeek, Mistral, Llama and more — all on TypingMind with your own API keys.

Is the Cross Origin Isolation AI skill free?

Yes. It is published on GitHub by thedaviddias under the MIT license. You only pay your own AI provider for the tokens you use.

What are AI skills?

An AI skill is a reusable instruction bundle that teaches an AI model how to do one specific task. It follows the open Agent Skills format: a SKILL.md file with a name and description, plus any scripts, templates or reference files the model may need. The model reads the instructions only when your request matches the skill, so an installed skill costs nothing until it is used.

How are AI skills different from plugins or MCP servers?

A plugin or MCP server gives a model new tools to call — code that runs somewhere and returns a result. An AI skill gives the model knowledge and process instead: how to approach a task, which steps to follow, what good output looks like. Skills are plain Markdown, so they need no server, no API key and no runtime, and they work with any model.

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Overview

Installation

Install in TypingMind

Install in another agent

Use it in TypingMind

Works with any AI model

Skill instructions

Use COOP, COEP, and CORP for cross-origin isolation when needed

Quick Reference

Check

Fix

Explain

Code Review

Bundled files

Frequently asked questions

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