arktype-validation

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