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Cross-Origin Isolation Review

Reviews web apps for COOP/COEP/CORP header setup needed for cross-origin isolation

Source Download skill
Repository
thedaviddias/Front-End-Checklist
Stars
74,632
Licence
MIT
Files
2 files

What it does

When installed, the agent gets a checklist-style guide for reviewing a website's security headers and embedded resources so that it can enable cross-origin isolation, a browser mode needed for features like SharedArrayBuffer. The agent will check whether the app needs the Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy headers, whether third-party scripts, iframes, workers and fonts are compatible, and whether the page actually becomes crossOriginIsolated in the browser. It is written as guidance for review, not as an automated tool.

Great for

  • Web developers building apps that use SharedArrayBuffer or heavy web workers, such as browser editors or media tools
  • Security-minded engineers auditing headers for XS-Leak and opener-based attack risk
  • Teams planning a careful rollout of COOP/COEP who want a structured review of third-party embeds

Skip it if

  • Simple static sites or apps without advanced browser features, where enabling isolation adds breakage risk for no benefit
  • Non-developers trying to fix a live site without access to server configuration, since incorrect headers can break embeds and logins
  • Anyone expecting a complete security audit; the skill is a focused checklist and does not scan a live site

Try asking

  • “Review my server headers and tell me whether I need COOP and COEP for SharedArrayBuffer”
  • “Audit the third-party scripts and iframes on my app before I enforce COEP”
  • “Check whether my page becomes crossOriginIsolated after I add these headers”
  • “Flag any responses or popup integrations that would break once isolation is enforced”
Step-by-step guide: how to use Cross-Origin Isolation ReviewInstall, first run, examples, tips and FAQs

Install in 3 steps

  1. 1

    Download the skill

    The ZIP contains the 2 original files, the MIT licence and an attribution note.

    cross-origin-isolation.zip
  2. 2

    Add it to your agent

    Claude Code (all projects)

    mkdir -p ~/.claude/skills && unzip cross-origin-isolation.zip -d ~/.claude/skills/

    Claude Code / Agent SDK (this project only)

    mkdir -p .claude/skills && unzip cross-origin-isolation.zip -d .claude/skills/

    Claude apps (web/desktop): Settings → Capabilities → Skills → Upload skill, and choose the ZIP.

  3. 3

    Ask for the task

    No special command needed — the agent reads the skill's description and loads it when your request matches. Try one of the prompts above.

Get better results

  • Give the agent your actual response headers and list of embedded third-party resources so it can check compatibility concretely
  • Test in a real browser and confirm self.crossOriginIsolated is true before relying on isolated features
  • Roll out in report-only or staging first, since COEP can silently block cross-origin assets

What's inside

  • references/rule.md
  • SKILL.md

Redistributed unmodified from thedaviddias/Front-End-Checklist under the MIT licence. The assessment was drafted with AI from the skill's files on 2026-10-29. Skills can instruct your agent to run code — read SKILL.md and any scripts before installing.