tsconfig

Development

TypeScript config conventions for this monorepo: the two-base layering, the eight leaf tiers, and the never-redeclare list. Use when adding a package, editing any tsconfig.json, picking a tier for a new app, or debugging module resolution.

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tsconfig conventions

Every package here is source-only .ts: exports point at ./src/*.ts, there is no build step, and consumers (Bun, Vite, WXT, Tauri, the Cloudflare Worker) operate on raw .ts. That single fact decides the whole config.

The one rule

A leaf tsconfig.json may set only: types, library-only strictness (noUnusedLocals/noUnusedParameters), checkJs (SvelteKit), and genuinely package-specific options (jsx, paths, customConditions, include).

Anything else belongs in a base. If a leaf option repeats a base value or a TypeScript default, delete it.

Two base files

tsconfig.base.json   universal: target/lib[ESNext], module preserve, strict,
                     noEmit, isolatedModules, verbatimModuleSyntax, types []
tsconfig.dom.json    extends base; its ONLY job is lib [ESNext, DOM, DOM.Iterable]

There is no tsconfig.base.lib.json and no project references. Source-only packages never emit, so composite/declaration/outDir have no place here.

Module strategy: one, repo-wide

module: "preserve" + moduleResolution: "bundler". preserve implies bundler (TS 5.4+); the explicit pair is kept for legibility. Never use NodeNext anywhere: nothing in this repo is published as emitted Node ESM, and bundler resolution already reads package.json imports/exports.

The eight leaf tiers

Pick the tier, copy the shape, change nothing else.

Tier	`extends`	Leaf adds
Bun library	`"../../tsconfig.base.json"`	`types:["bun"]`, `noUnusedLocals`, `noUnusedParameters`
Node library	`"../../tsconfig.base.json"`	`types:["node"]`, `noUnusedLocals`, `noUnusedParameters`
Svelte library	`"../../tsconfig.dom.json"`	`types:["bun"]`, `noUnusedLocals`, `noUnusedParameters`
SvelteKit app	`["../../tsconfig.base.json", "./.svelte-kit/tsconfig.json"]`	`checkJs:true`, `types:["bun"]`
Cloudflare Worker	`"../../tsconfig.base.json"`	`jsx`, `jsxImportSource`, `types`, `include`
Bun app	`"../../tsconfig.base.json"`	`types:["bun"]`, `include`
Astro app	`["../../tsconfig.base.json", "astro/tsconfigs/strict"]`	astro `include`/`exclude`
WXT extension	`["../../tsconfig.dom.json", "./.wxt/tsconfig.json"]`	`customConditions`, `paths`, `include`

A generated config (./.svelte-kit/tsconfig.json, ./.wxt/tsconfig.json) goes last in the array so its lib/module win where they must. Never hand-edit a generated config.

The two canonical library shapes in full:

// bun library: packages/workspace, filesystem, util, sync, cli, ...
{
	"extends": "../../tsconfig.base.json",
	"compilerOptions": {
		"types": ["bun"],
		"noUnusedLocals": true,
		"noUnusedParameters": true
	}
}

// svelte library: packages/ui, svelte-utils
{
	"extends": "../../tsconfig.dom.json",
	"compilerOptions": {
		"types": ["bun"],
		"noUnusedLocals": true,
		"noUnusedParameters": true
	}
}

Never redeclare these (base value or TS default)

Putting any of these in a leaf is dead weight. Delete on sight.

Do not write in a leaf	Why
`module: "preserve"`	already in `tsconfig.base.json`
`moduleResolution`, `target`, `noEmit`, `strict`, `isolatedModules`	already in the base
`lib: ["ESNext"]`	the base default; use `tsconfig.dom.json` if you need DOM
`noPropertyAccessFromIndexSignature: false`	that is already the TS default
`useDefineForClassFields: true`	default when `target` >= ES2022
`forceConsistentCasingInFileNames`	default `true` since TS 5.0
`resolvePackageJsonExports`	default `true` under `moduleResolution: bundler`
`sourceMap`	no-op under `noEmit`
single-element `extends` array	use the string form: `"extends": "../../tsconfig.base.json"`

`types` is opt-in, on purpose

The base sets types: [] to disable auto-inclusion of every node_modules/@types package. Each leaf opts in: ["bun"] for almost everything, ["node"] for the one package that uses @types/node. Do not hoist ["bun"] to a base: a package without @types/bun installed would then fail with Cannot find type definition.

`include` rules

TypeScript does not merge include across extends. A leaf include fully replaces the inherited one. For SvelteKit apps this means: do not set your own include, or you drop the generated ambient.d.ts/$types globs.
Only set include when you must narrow scope for a real reason; comment why.

Adding a new package

Scaffold via the monorepo skill's boilerplate.
Pick a tier from the table above; copy that exact shape.
package.json uses exports only, no main/types. Entry point is ./src/index.ts.
bun install at the repo root, then bun typecheck.

Background

The full rationale, the migration that established this layout, and the baseline typecheck state are in specs/20260522T190000-modernize-monorepo-tsconfig.md.