ArkType Validation

Overview

ArkType is a TypeScript-native runtime validation library that defines schemas using string expressions mirroring TypeScript syntax, providing editor autocomplete, syntax highlighting, and optimized validators. Use when building type-safe APIs, validating JSON payloads, or replacing Zod with a more TypeScript-idiomatic approach. Not suitable for projects that need Zod ecosystem compatibility or JSON Schema output.

Package: arktype

Quick Reference

Pattern	Usage
`type({ key: "string" })`	Define object schema
`type("string")`	Primitive type
`"string.email"`, `"string.url"`	Built-in string validators
`"string.trim"`, `"string.lower"`	Built-in string morphs (transforms)
`"string.json.parse"`	Parse JSON string to validated object
`"number > 0"`, `"string >= 1"`	Inline constraints
`"string \| number"`	Union types
`"'a' \| 'b' \| 'c'"`	String literal unions
`"string[]"`	Array types
`"key?": "string"`	Optional properties
`"key = 'default'"`	Default values
`.pipe()`, `.to()`	Transform output (morphs)
`.narrow()`	Custom validation (like Zod refine)
`.pick()`, `.omit()`	Object property selection
`.merge()`	Combine object types
`scope({...}).export()`	Named type scopes with cross-references
`type("<t>", { box: "t" })`	Generic type definitions
`type.errors`	Error handling (check `instanceof type.errors`)
`.assert(data)`	Throws on invalid input instead of returning
`"(number % 2)#even"`	Branding — type-only validated marker
`"0 <= number <= 100"`	Compact range constraints
`configure()`	Global defaults (from `arktype/config`)
`match()`	Type-safe pattern matching (2.1)
`"+" : "reject"`	Inline undeclared key handling
`arkenv({ PORT: "number" })`	Typesafe env var validation (ArkEnv)
`arkenvVitePlugin(Env)`	Build-time env validation for Vite

Common Mistakes

Mistake	Fix
`type("string.email()")` with parens	`type("string.email")` (no parens)
Checking errors with `=== null`	Use `instanceof type.errors`
`{ key: "string?" }` for optional	`{ "key?": "string" }` (question mark on key)
Importing from `arktype/types`	Import `type` and `scope` from `"arktype"`
Nested `type()` in string expressions	Use `scope()` for cross-referencing types
Raw `.pipe()` without error handling	Use `.pipe.try()` for operations that can throw
`"string.lowercase"` for case morph	`"string.lower"` (also `"string.upper"`)
Configuring after importing `arktype`	Import `arktype/config` before `arktype`
Manual `process.env` parsing	Use `arkenv()` for auto-coercion and validation

Delegation

Use this skill for ArkType schema definitions, runtime validation, morphs/transforms, scopes, and type inference. For Zod-based validation, delegate to the zod-validation skill.

References

Schema Types — primitives, string keywords, number constraints, objects, arrays, tuples, unions, optional, defaults
Morphs and Scopes — pipe, morph transforms, narrow validation, scopes, recursive types, generics, global configuration, pattern matching
Common Patterns — JSON parsing, form validation, API responses, error handling, ArkEnv environment variables, Vite plugin, comparison with Zod

arktype-validation

ArkType Validation

Overview

Quick Reference

Common Mistakes

Delegation

References