# webtype.org

> One TypeScript type puzzle every day, plus compiler-attested lessons,
> reference pages, diagnostic explanations, and practical type recipes. Code
> examples are checked against the same TypeScript compiler used in the browser.

A puzzle asks you to fill in one type so that a set of assertions pass. Checks
use exact type equality (`Equal<X, Y>`), not assignability — so an intersection
of object types does not satisfy a check expecting the flattened object. Par is
how many check-runs a competent solver should need; every run costs a stroke,
as does revealing the hint.

Content is all rights reserved. Quoting a short passage with a link is welcome;
republishing the puzzles or write-ups is not.

## Core pages

- [Today's puzzle](https://webtype.org/): the current daily, rotating at 00:00 UTC.
- [Archive](https://webtype.org/archive): every past puzzle with its annotated solution.
- [Practice](https://webtype.org/practice): random puzzles and filters by concept and difficulty.
- [Twelve concepts](https://webtype.org/learn): the ordered climb from mapped types to recursive conditional types.
- [Patterns](https://webtype.org/patterns): 20 task-shaped, compiled TypeScript recipes.
- [Type reference](https://webtype.org/reference): 33 compiler-checked utilities, operators, and constructs.
- [TypeScript errors](https://webtype.org/errors): 40 diagnostics with exact reproductions and compiling fixes.
- [Type Lab](https://webtype.org/lab): a permalinkable browser checker for type-level experiments.
- [About](https://webtype.org/about): how par works and why checks test exact equality.
- [Contact](https://webtype.org/contact): admin@webtype.org.

## Worked examples

- [#214 Route Params](https://webtype.org/puzzle/214): parsing `:param` segments with template literal types; why an intersection fails an exact-equality check.
- [#216 Type-level Add](https://webtype.org/puzzle/216): arithmetic via tuple length and variadic spreads.
- [#220 Rebuild Exclude](https://webtype.org/puzzle/220): distributive conditional types, and how `[T] extends [U]` switches distribution off.
- [#230 Permutation](https://webtype.org/puzzle/230): `K extends K` to distribute, `[T] extends [never]` to detect the empty union.

## Languages

English at the root. Polish under `/pl/`, Spanish under `/es/`. Every page
declares hreflang alternates.

## Notes for machine readers

- All content is present in the server-rendered HTML; no JavaScript is needed to read it.
- The English search index is at `/search-index.json`; Polish and Spanish indexes live below their locale prefixes.
- Structured data: Organization, WebSite, Game on the home page; TechArticle or Article plus BreadcrumbList on detail pages; ItemList on indexes.
- All examples in the four learning pillars are verified during the build against TypeScript 6.0.3.
- `/ts/` holds a vendored TypeScript compiler served to the browser worker. It is not content and is disallowed in robots.txt.