Joan León Posts
All the articles I've posted.
A skill that knows nothing: the architecture of Modern Web Guidance
Published:Modern Web Guidance doesn't keep the knowledge in the skill, it teaches the agent to retrieve it. Local semantic search with MiniLM and TensorFlow.js, guides with their own grader, and empirical calibration of the content.
The CrUX 28-day rolling window
Published:How the CrUX 28-day rolling window actually works, what each source publishes, and why p75 takes so long to move even though the data is only two days old.
A 301 on every click: the trailing slash that slowed down all internal navigation
Published:A real finding on skills.addy.ie: every internal link triggered a 301 redirect on Netlify because of a missing trailing slash. What it costs the UX, how I spotted it in DevTools, the quick fix I first thought of, and the underlying solution (Astro directory format + trailingSlash: 'always'). With Network panel evidence before and after.
Keep-Alive is not Cache-Control: anatomy of a network waterfall
Published:A real audit case: two heavy images (608 KB and 403 KB) over HTTP/1.1 with Connection: Keep-Alive but no Cache-Control. Why they are different things, what HTTP/2 fixes and how preconnect gets ahead of the handshake. With an interactive waterfall demo.
The mystery of the self-repainting #document: Paint flashing and composited layers
Published:Why the #document layer racks up hundreds of repaints at rest because of a ticker animated with transform, how to catch it with the Layers tab and Paint flashing, and how to promote the element to its own composited layer with will-change.
Antigravity Skills: advanced YAML frontmatter configuration
Published:The kind, model, temperature, max_turns and tools fields in SKILL.md frontmatter let you precisely control how each agent runs in Antigravity. A practical guide to the extended fields that Google hasn't officially documented yet.
Video editing in the browser with WebGPU
Published:WebGPU enables real-time video effects and transformations in the browser. Practical implementation with benchmarks and real-world limitations.
Forced Synchronous Layout: how to detect and analyze it with DevTools
Published:How a scroll reset after mass DOM manipulation triggers a Forced Synchronous Layout, how to detect it in the Performance Panel and Selector Stats in Chrome DevTools, and how to fix it with requestAnimationFrame.