Review communication between different websites for security issues. Inspect code and browser behavior to identify overly broad CORS permissions, unchecked message senders, missing request protections, and unsafe redirects, then propose fixes and browser checks.
Use when reviewing scripts, client components, bundles, or runtime behavior related to Handle cross-origin requests securely. Inspect both source code and the browser execution path so fixes target the real bottleneck or bug.
Review the instructions the agent will receive before you install.
The Same-Origin Policy is the browser's primary defense against malicious sites stealing data or performing actions on behalf of your users. Misconfiguring CORS or failing to validate postMessage origins can allow attackers to bypass this protection — reading private data, submitting forms as users, or injecting content into your pages.
next, redirect, or callbackUrlCheck this code for insecure cross-origin patterns: missing origin validation in postMessage listeners, overly permissive CORS settings, and missing CSRF protections. Flag redirect parameters that accept arbitrary external URLs.
Add origin validation to postMessage listeners and review CORS configuration to ensure it's not overly permissive for authenticated routes. Reject or allow-list untrusted redirect destinations before navigating.
Explain the Same-Origin Policy, how CORS works, and how to securely use postMessage for cross-origin communication.
Review scripts, client components, and browser execution paths related to Handle cross-origin requests securely. Flag exact imports, event handlers, runtime side effects, or blocking operations that violate the rule, and state how the change should be verified in the browser. Check login, logout, SSO, and return-to flows for open redirects.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/javascript/cross-origin-security
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Create and review custom 404 pages that help visitors recover from broken or moved links through search and navigation. Check the rendered page and HTTP response so missing content returns a proper 404 status.
Audit or create a dedicated About page that explains a website’s purpose and identifies its people or organization. Review the rendered output and supporting information, including expertise and contact details, to find gaps.
Review and add automated accessibility checks for components, pages, and continuous integration workflows. Use axe-based tools to detect structural and attribute issues, while identifying checks that still need keyboard or screen reader testing.
Review sign-in, registration, multi-factor authentication, and account recovery for accessibility barriers. Find blocked paste, difficult code entry, and inaccessible backup methods, then suggest authentication paths that support password managers, autofill, or device approval.
Review form errors, success messages, and live updates so screen reader users receive important notifications. Check the HTML delivered to the browser, announcement settings, display duration, and dismissal controls, then identify specific elements that need changes.
Review HTML tables so screen reader users can understand how headers and data relate. Check header markup, table descriptions, and merged cells, then identify specific fixes and ways to verify them.