---
title: "Server response (TTFB) is slow (perf/ttfb-slow)"
description: "perf/ttfb-slow: Every millisecond before the first byte delays everything else."
canonical: https://void-design.vercel.app/rules/perf/ttfb-slow
lastModified: 2026-09-16
---

# Server response (TTFB) is slow

`perf/ttfb-slow` · severity **warn** · category Performance · detected by `void perf` and `void audit`

## Why it matters

Every millisecond before the first byte delays everything else. TTFB above ~800 ms usually makes a good LCP impossible.

## How to fix it

Serve static or prerendered HTML from a CDN edge, cache dynamic HTML with s-maxage + stale-while-revalidate, stream the shell early, and remove redirects on the entry URL.

## References

- https://web.dev/articles/optimize-ttfb

## More performance rules

`void perf` reports 25 rules in this category. Core Web Vitals and bytes: LCP, CLS, TBT, TTFB, JavaScript, CSS, fonts, images, caching and compression, measured as the median of several runs on a throttled mobile and a desktop profile.

- `lcp-slow` Largest Contentful Paint is slow — [perf/lcp-slow](https://void-design.vercel.app/rules/perf/lcp-slow)
- `cls-high` Cumulative Layout Shift is high — [perf/cls-high](https://void-design.vercel.app/rules/perf/cls-high)
- `fcp-slow` First Contentful Paint is slow — [perf/fcp-slow](https://void-design.vercel.app/rules/perf/fcp-slow)
- `tbt-high` Main thread is blocked by long tasks during load — [perf/tbt-high](https://void-design.vercel.app/rules/perf/tbt-high)
- `js-budget` First-load JavaScript exceeds the budget — [perf/js-budget](https://void-design.vercel.app/rules/perf/js-budget)
- `css-budget` CSS transfer exceeds the budget — [perf/css-budget](https://void-design.vercel.app/rules/perf/css-budget)
- `font-budget` Web font transfer exceeds the budget — [perf/font-budget](https://void-design.vercel.app/rules/perf/font-budget)
- `too-many-fonts` Too many font files are downloaded — [perf/too-many-fonts](https://void-design.vercel.app/rules/perf/too-many-fonts)

Detected by `void perf` and `void audit`. Explain it in a terminal: `void rules perf/ttfb-slow`