bun-expert

Bun Runtime Development Guide

This skill is intentionally grounded in official Bun documentation. Bun moves quickly, so prefer current docs over hard-coded release timelines or benchmark claims.

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Recent Capability Radar

Bun ships new built-ins constantly. This list covers what landed roughly between Bun 1.3 (Oct 2025) and Bun 1.3.14 (May 2026) — the kind of thing a model's training data likely predates. For anything newer, check https://bun.com/blog before assuming a capability doesn't exist.

Reach for these instead of the dependency you'd otherwise install:

• Bun.SQL: one client for Postgres, MySQL/MariaDB, and SQLite — skip pg, mysql2, or postgres.
• Bun.redis: native Redis/Valkey client — skip ioredis/node-redis.
• Bun.secrets: OS-keychain-backed credential storage — skip keytar.
• Bun.YAML.parse/.stringify: built-in YAML — skip js-yaml/yaml.
• CompressionStream/DecompressionStream now support "brotli" and "zstd" formats, not just gzip/deflate.
• Bun.stripANSI, URLPattern, and DisposableStack/AsyncDisposableStack are built in — skip strip-ansi and userland URL-pattern/cleanup helpers.
• Bun.markdown (.html/.render/.react): built-in CommonMark+GFM parser; bun ./file.md renders Markdown in the terminal — skip markdown-it/marked for common cases.
• Fake timers landed in bun:test (useFakeTimers, advanceTimersByTime, setSystemTime, useRealTimers) — skip sinon/@sinonjs/fake-timers.
• HTML-entrypoint dev server gained hot module replacement via import.meta.hot — skip a separate Vite/webpack dev server for simple frontends.
• bun install --linker=isolated with globalStore = true (or BUN_INSTALL_GLOBAL_STORE=1): still-experimental global virtual store for much faster warm installs.
• Still experimental, don't default to these in production: Bun.WebView (browser automation without Puppeteer/Playwright) and HTTP/3 over QUIC in both Bun.serve({ http3: true }) and fetch({ protocol: "h3" }).

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Built-in API Map

Need	Bun API
HTTP server + WebSockets	Bun.serve()
SQL databases	sql, SQL, Bun.sql, Bun.SQL
S3-compatible storage	s3, S3Client
Redis	redis, RedisClient
Scheduled tasks (cron)	Bun.cron, Bun.cron.parse
Image processing	Bun.Image, Blob#image(), Bun.file().image()
Browser automation	Bun.WebView
Markdown rendering	Bun.markdown.html, Bun.markdown.render, Bun.markdown.react
Shell scripting	Bun.$ / $
Local files	Bun.file, Bun.write
SQLite (embedded)	bun:sqlite
Password hashing	Bun.password
PTY-backed subprocesses	Bun.Terminal, Bun.spawn({ terminal })

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Deep-Dive References

Reference	Contents
references/builtin-apis.md	Bun.serve, HTTP/3, WebSockets, SQL, S3, Redis, Bun.Image, Bun.WebView, Markdown, cron, shell, PTY, filesystem, and crypto APIs
references/package-management.md	Installs, lockfiles, isolated linker, global virtual store, catalogs, and lifecycle-script security
references/testing-and-bundling.md	bun test usage, suite-splitting flags, mocking patterns, bun build CLI and API
references/node-migration.md	Practical Node-to-Bun migration steps and compatibility guidance

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Authoritative Docs

• https://bun.com/docs
• https://bun.com/blog