boolean()

Creates a validator that accepts boolean values. Supports string and numeric coercion.

Signature

function boolean(): BooleanValidator

Accepted Values

Input	Result	Notes
true	✅ true	Actual boolean
false	✅ false	Actual boolean
"true"	✅ true	Case-insensitive, trimmed
"false"	✅ false	Case-insensitive, trimmed
"TRUE"	✅ true	Case-insensitive
"1"	✅ true	String "1"
"0"	✅ false	String "0"
"yes"	✅ true	Case-insensitive
"no"	✅ false	Case-insensitive
"on"	✅ true	Case-insensitive
"off"	✅ false	Case-insensitive
"y"	✅ true	Shorthand "yes"
"n"	✅ false	Shorthand "no"
"t"	✅ true	Shorthand "true"
"f"	✅ false	Shorthand "false"
1	✅ true	Number 1
0	✅ false	Number 0
2	❌ Type error	Only 1 and 0 are accepted
null	❌ Type error

Refinements

boolean() has no type-specific refinements. It only has the chainable methods (.optional(), .default(), .describe(), .secret(), .validate()).

Examples

Basic boolean

const env = defineEnv({
  DEBUG: boolean(),
})
// With process.env.DEBUG = "true"
// env.DEBUG → true

Optional boolean

const env = defineEnv({
  FEATURE_X_ENABLED: boolean().optional(),
})
// env.FEATURE_X_ENABLED: boolean | undefined

Boolean with default

const env = defineEnv({
  ENABLE_LOGGING: boolean().default(true),
})
// env.ENABLE_LOGGING: boolean (defaults to true if not set)

Common patterns

const env = defineEnv({
  // Feature flags
  ENABLE_NEW_DASHBOARD: boolean().default(false),
  SHOW_EXPERIMENTAL: boolean().optional(),

  // Logging controls
  DEBUG: boolean().default(false).describe("Enable debug logging"),
  VERBOSE: boolean().default(false),
})