My API Responded in 4 ms, but Navigation Still Felt Slow

I was debugging an internal project management application built with SvelteKit and a Rust API. Locally, navigation felt almost instant. On the VPS, opening the Tickets, Timeline, and OpenSpec docs pages felt noticeably slower. Clicking a ticket also took too long before the preview panel became useful. My first assumption was infrastructure: Maybe the VPS was underpowered. Maybe PostgreSQL queries were slow. Maybe the reverse proxy added latency. Maybe SvelteKit SSR was taking too long. The measurements pointed somewhere else. The Baseline I started with the feature list endpoint used by both Tickets and Timeline. For a project with 52 tickets: Metric Result API response time ~4 ms Response size 353,956 bytes Number of tickets 52 The API was not slow. But it was returning around 354 KB for a list of only 52 items. The SvelteKit route payload showed the same pattern: Route Data payload Tickets 349,857 bytes Timeline 354,731 bytes This explained why local testing was misleading. On localhost, transferring and parsing a few hundred kilobytes is easy to miss. Once the app runs behind a VPS, reverse proxy, TLS, and a real network connection, the payload becomes much more visible. What Was Inside the Payload? I broke down the feature response by field. The descriptions alone accounted for: 296,177 bytes That was more than 80% of the complete response. The list endpoint was returning something similar to this for every ticket: interface FeatureListItem { id : string ; title : string ; status : string ; priority : string ; storyPoints : number | null ; dueDate : string | null ; description : string | null ; checkoutCommand : string | null ; openSpecCommand : string | null ; } The problem was not that these fields were useless. They were useful on the ticket detail panel. They were not useful when rendering the initial list. Timeline was even more wasteful. It used ticket status, dates, dependencies, and assignees, but still downloaded every full Markdown description. The D