Biome 2.5.15: type-inference speedups, nursery rules, HTML formatter (30 Sep 2026)

No affiliate links. This is a frontend toolchain note from public Biome docs and the GitHub release. ShopperCove has not migrated a production monorepo to 2.5.15 for this article.

Why 2.5.15 now

Biome’s npm latest is @biomejs/biome@2.5.15, published 30 Sep 2026 (registry time 2026-09-30T15:23:18.673Z; GitHub release 2026-09-30T15:23:21Z). Cont11 already covered pnpm 12.9.1; this slot is the freshest Biome patch among Biome / Bun / Prettier signals as of 5 Oct 2026 sources—not a Bun 1.4.2 or Prettier 3.9 rehash.

Baseline for the 2.5 line remains the Biome v2.5 blog (5 Jun 2026): 500+ lint rules, plugin includes + plugin code fixes, delimiterSpacing, CLI --watch, linter.rules.preset, go-to-definition, and related LSP/CLI work. 2.5.15 is the patch you pin after that line when you want the late-September inference and formatter wins.

What 2.5.15 highlights (release notes)

From the GitHub release for @biomejs/biome@2.5.15:

Performance

• Type inference — significant speedups; release notes cite roughly ~2–240× on benchmarks for heavy libraries such as Zod, Valibot, Arktype, Effect, Kysely, and Drizzle (affects typed rules).
• HTML formatter — up to ~4× faster.
• Indexing / analysis of big files — up to ~2× (most visible with project and types lint rules).

New nursery rules (examples)

Rule	Intent (from release notes)
noReactObjectTypeAsDefaultProp	Disallow array/object/function default props in React components
noSvelteExportLet	Prefer $props() over legacy export let
useSvelteKitRuneImports	Prefer $app/state over deprecated $app/stores
useLogicalProperties	Prefer CSS logical properties; direction option ltr (default) or rtl
noMeaninglessVoidOperator	Flag unnecessary void (allows discarded calls, thenables, void 0, never)
useStrictBooleanExpressions	Report ambiguous truthiness such as if (value) on `number	undefined`
noAstroConflictingSetDirectives	Flag conflicting set:html / set:text / children
noTailwindRawColors	Discourage raw palette classes like bg-pink-500 in favor of design tokens
noSelfImport	Forbid a module importing itself
usePromiseRejectErrors	Require Error objects as Promise rejection reasons
noMisplacedListElements	Require <li> under <ul> / <ol> / <menu> when parent is an HTML element

Nursery rules are opt-in until you promote them. Do not treat nursery as “recommended” by default.

Notable fixes / behavior

• Astro multiline expressions indent correctly under biome check --write; Astro expressions also format via biome format.
• Configuration file errors are retained and checked before commands (no silent ignore).
• Unix daemon socket restricted to the running user (0600 under a biome-daemon cache directory).
• Tailwind class detection in Svelte / Vue / Astro class attribute expressions without a merge helper.
• Domain disable no longer turns off rules that also belong to another enabled domain.
• HTML parser mismatch reporting and several Svelte comment/indent fixes.

ShopperCove is not attaching CVE IDs to this note.

Hands-on upgrade checklist

1. Inventory: npx @biomejs/biome --version (or your package-manager pin) and whether CI uses npm/pnpm/yarn/bun.
2. Confirm registry: npm view @biomejs/biome version → expect 2.5.15 as of 5 Oct 2026 sources.
3. Pin exact: follow Getting started — install with -E / --save-exact (npm i -D -E @biomejs/biome@2.5.15).
4. Migrate if needed: if you still use deprecated linter.rules.recommended, run biome migrate --write toward linter.rules.preset (v2.5 blog).
5. Staging bump: upgrade on a branch; run biome check (and format) before enabling new nursery rules.
6. Typed-rule projects: re-time CI after 2.5.15 if you lean on project/types rules—the release’s main claim is inference cost.
7. HTML / Astro / Svelte / Vue stacks: re-run format+lint once; expect Astro expression and Svelte comment indent diffs.
8. Do not invent urgency: this is a docs/release checklist, not a security advisory.

ShopperCove did not change production Biome versions for this article. Prefer biomejs.dev and the GitHub release over third-party roundups.

Bottom line

Biome 2.5.15 (30 Sep 2026) is worth the pin if you care about type-inference cost, HTML format speed, and late nursery coverage for React / Svelte / Astro / CSS logical properties. Start from the v2.5 feature baseline, then land on 2.5.15. No affiliate.

Sources

• https://github.com/biomejs/biome/releases/tag/%40biomejs%2Fbiome%402.5.15
• https://biomejs.dev/blog/biome-v2-5/
• https://biomejs.dev/guides/getting-started/
• https://www.npmjs.com/package/@biomejs/biome
• https://registry.npmjs.org/@biomejs/biome/2.5.15
• https://biomejs.dev/

Related

• https://www.shoppercove.com/blog/vite-plus-1-0-unified-toolchain-october-2026
• https://www.shoppercove.com/blog/eslint-10-12-release-october-2026
• https://www.shoppercove.com/blog/oxlint-1-87-react-suggestions-a11y-fixes-october-2026
• https://www.shoppercove.com/blog/typescript-eslint-8-71-no-unsafe-enum-assignment-october-2026
• https://www.shoppercove.com/blog/astro-starlight-0-42-popover-js-dist-october-2026
• https://www.shoppercove.com/blog/playwright-1-63-test-locks-october-2026
• https://www.shoppercove.com/blog/webpack-5-111-esm-output-stable-september-2026
• https://www.shoppercove.com/blog/nodejs-26-lts-october-2026-schedule-change