Layer Ownership Checklist

Pack: performance Parent skill: Performance Triage And Bottleneck Hunting Source: performance/performance-triage-and-bottleneck-hunting/references/layer-ownership-checklist.md Use this reference to avoid optimizing the wrong layer.

Server / API dominated

• slow TTFB even before the browser starts rendering
• endpoint p95 is high
• expensive serialization or repeated I/O per request
• database or external service dominates the request path

React dominated

• input lag after the data already arrived
• one local interaction rerenders a large subtree
• DevTools shows expensive renders rather than slow network

Next.js route / bundle dominated

• route is dynamic without needing to be
• too many client boundaries near the top of the tree
• hydration cost is large on first load
• third-party scripts or large client bundles dominate startup

Network / third-party dominated

• waterfall from multiple remote calls
• blocking scripts or remote assets delay route completion
• backend is fine locally but slow with real network conditions

Default rule

Name the bottleneck owner before proposing a fix. If the owner is unclear, keep measuring instead of optimizing.