Write cutting-edge and modern native CSS. Apply this skill whenever writing, reviewing, or refactoring CSS for components, layouts, design systems, or theming, even if the user doesn't say "modern CSS" explicitly. Covers a self-contained design-token scale (color, size, shadow, ease, type), cascade layers (@layer), @scope for component isolation (donut scopes, :scope specificity, scoping proximity), container queries, :has(), OKLCH/color-mix, native nesting, subgrid, fluid typography via clamp(), scroll-driven animations, logical properties, and concrete native replacements for SCSS mixins, maps, and variables.
Apply this skill whenever the task involves web security: writing or auditing HTTP security headers, configuring CSP, CORS, HSTS, or Permissions-Policy, sanitising untrusted HTML (Sanitizer API / DOMPurify), implementing Trusted Types to prevent DOM-XSS, setting up the Reporting API to capture CSP/COEP/deprecation violations, hardening cookies (SameSite, HttpOnly, Secure, Partitioned), implementing WebAuthn / Credential Management, using Web Crypto for client-side cryptography, or auditing code for XSS, CSRF, clickjacking, MIME-sniffing, mixed content, or cross-origin data leakage. Triggers on keywords: XSS, CSRF, CSP, CORS, HSTS, SameSite, innerHTML, eval, Trusted Types, Sanitizer, ReportingObserver, WebAuthn, cross-origin, clickjacking, Content-Security-Policy, Referrer-Policy, Permissions-Policy, subresource integrity, cookie security, secure context, same-origin, mixed content.
Patterns for invoking the GitHub CLI (gh) from agents. Covers structured output, pagination, repo targeting, search vs list, gh api fallback.
Audit and update durable architecture guidance after a cross-layer implementation, file move, package boundary change, coverage config change, or SDTE feature. Use when agent needs to reconcile AGENTS.md, package AGENTS.md files, local .agents/skills, older specs, dynamic imports, and test or coverage configuration with the architecture that was actually implemented.
Run the Spec → Design → Tasks → Execution workflow for non-trivial work — produces /specs/<feature>/{spec,design,tasks}.md, drives atomic per-task execution, and ends with a Review phase. Invoke when starting a new package, new game system, GameState shape change, or any change touching > 3 files or crossing a layer boundary.
Best practices for building scalable plain Web Components without turning custom elements into “god objects”. Provides patterns that keep Web Components modular, reusable, maintainable, and focused on UI concerns.
Common patterns and best-practices for writing tests (unit tests & E2E tests)
Safely evolve GameState shape — bump stateVersion, write a pure migration function, update replay fixtures and snapshot baselines