Tim Kadlec

@tkadlec

Principal Product Manager @cloudflare—focused on performance and observability. Co-chair of Taller than my photo looks.

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Tim Kadlec@tkadlec· Mar 26

p75 and p90 JavaScript bytes on the web have exploded since May, 2025—easily the largest 10 month period based on HTTP Archive data since 2023. The long-tail is getting worse, very quickly. Gemini, what happened in May 2025?

Tim Kadlec@tkadlec· Oct 31

Always, always happy to see @yoav.ws get a shout-out. So much incredible work has happened because of him. Most recent example—speculation rules in WebKit. #perfnow

Tim Kadlec@tkadlec· Oct 31

I have been sooooo looking forward to this! SPA heuristics are gonna be such a huge step forward for measuring perf on the web and finally having hard data on the perf impact. @mmocny.com #perfnow

Michal Mocney presenting at perfnow about SPA heuristics, demoing being able to measure LCP and other metrics on soft navigations

Tim Kadlec@tkadlec· Oct 30

@inesakrap.bsky.social starting her #perfnow talk with Lego's and Bluey has me already a fan.

Tim Kadlec@tkadlec· Oct 15

This is super exciting, particularly knowing Safari has it in Tech Preview so we're _this_ close to having it cross-browser. Also fun to watch the rollout through the lens of Cloudflare's Web Analytics.

Tim Kadlec@tkadlec· Jul 2

👀 Safari plans to ship LCP and INP in 2025?! Be still my beating heart. webkit.org/blog/16458/a...

Tim Kadlec@tkadlec· Jul 1

This is incredible data from @dbelson.com showing HTML requests from crawlers versus referrals from that platform. Very easy to see the cost of AI here. ClaudeBot: 70.9k requests : 1 referral (!!!) OpenAI: 1.6K : 1 Perplexity: 202.4 : 1 blog.cloudflare.com/ai-search-cr...

Tim Kadlec@tkadlec· Jun 22

Lake Superior remains undefeated

Tim Kadlec@tkadlec· May 26

Concur!

Tim Kadlec@tkadlec· Jan 31

Been wondering why a bunch of sites have been SUPER slow lately. Turns out it's the @1password.bsky.social chrome extension doing really bad things. :/ Gonna have to disable for awhile.

Chrome's performance timline, showing a 3.99s long task caused by a script injected by the 1Password Chrome Extension.

Screenshot showing the chunk of code (a mutation obsever) in the 1Password extension that seems to be the culprit.

Tim Kadlec@tkadlec· Dec 14

Basically doing the same thing.

Tim Kadlec@tkadlec· Nov 15

"Always iterate". @anniesullie.bsky.social Good advice for product management, performance experimentation and so much more. I'm a huge proponent of the "what's the least amount of work we can do to see if we're on the right path" approach. #perfnow

Annie Sullivan on stage at perfnow, with a slide showing the cycle of change - measure - learn

Tim Kadlec@tkadlec· Aug 2

Friendly reminder that when a third-party provider requires you to load their script in a render-blocking manner, their problems become your problems. Always build with resilience in mind.

This image shows the LCP metric from two page loads (same page, same location, same connection, same device). One is 1.96s, the other is 10.08s.

The difference is a third-party provider who was having server issues, causing their script to take 9.5s to load.

Tim Kadlec@tkadlec· Jul 14

Started working with these folks in mid-May and not gonna lie, pretty pleased with the progress they've made on INP in such a short span of time. From a p75 of 4.25s in April (90% of sessions having a poor experience) to a p75 of 225ms in June (9% of sessions have a poor experience).

Screenshot from Treo showing INP on mobile for the past year. There's a massive jump in INP performance in May, followed by another big one in June. INP went from 89.8% poor in April to 9% poor in June.

Tim Kadlec@tkadlec· Jun 8

Phew. What a difference a `:last` makes in jQuery. Third-party Shopify app with a very long list of selectors in a click handler. With the deprecated `:last` selector: ~616ms Without: ~16ms (Talked to the app devs and they're looking at it now so hopefully this gets fixed)