Bun performance tuning: push first paint and edge response to the limit
Around Bun's real bottlenecks, an actionable LCP / INP / CLS checklist.
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Quick answer
Why does my existing project break when I run it on Bun?
Native modules may be missing or APIs differ. Bootstrap new projects with bun first, then migrate legacy projects gradually and fill in types.
Machine-readable page data: /data/bun-performance-optimization.json
In-depth analysis
Bun unifies runtime, package manager, and bundler into one toolchain, beating Node on startup and install speed. It pairs especially well with AI coding workflows. Performance tuning concentrates on three fronts — build-time code splitting, edge caching, and zero runtime dependencies — to push first paint and response time to their floor.
// Local server + script runner with Bun (zero extra deps)
Bun.serve({ port: 3000, fetch: () => new Response('hi') });
// Install: bun install Run: bun run dev Build: bun build ./src/index.tsBun Performance Tuning · Key takeaways
- First-paint JS bundle audited
- Static assets hit edge long cache
- Core interaction INP measured ≤ 100ms
- Lighthouse hits the budget target
FAQ & pitfalls
How do I cache Bun build artifacts at the edge?
Artifacts use hash filenames with immutable long cache. Bun itself does not participate in runtime — static delivery is handled by the edge.
Explore the hub
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Git-driven Bun deployment in practice: commit to build, atomic publish to every edge node.
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Use Bun as a unified runtime, package manager, and bundler to speed up Node development and builds by several times.
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What readers are asking
Questions that keep coming back in reader feedback, already answered.
- 01
Why does the same project error out when I run it with Bun?
Native modules are missing, or some Node APIs behave differently under Bun. Pin the Bun version in CI; migrate older projects gradually and initialise new ones with Bun directly.
See the full guide → - 02
Why is my Astro component's interactivity not working?
Components ship as zero-JS HTML by default, so an interactive one needs a client:* directive (client:load, client:visible, …). Without it the script is never bundled into the page.
See the full guide → - 03
Why is my custom Tailwind v4 brand colour not applied?
Colours must be declared in @theme (for example --color-brand). A missing @tailwindcss/vite plugin, or a leftover v3 config, makes bg-brand silently render nothing.
See the full guide →