validate()

Validate a value against a Standard Schema.

validate() is a thin async wrapper around the Standard Schema ~validate protocol. It normalizes both sync and async schema libraries into a Promise<Result<T>>.

Signature

function validate<T>(
  value: unknown,
  schema: StandardSchemaV1<unknown, T>
): Promise<Result<T>>

Parameters

Parameter	Type	Description
value	unknown	The value to validate
schema	StandardSchemaV1<unknown, T>	Any Standard Schema-compatible schema (Zod, Valibot, ArkType, etc.)

Return value

Promise<Result<T>> — { ok: true, value: T } on success, { ok: false, error: ValidationError } on failure.

Example

import { validate } from 'flint';
import * as v from 'valibot';

const UserSchema = v.object({
  name: v.string(),
  age: v.number(),
});

const res = await validate({ name: 'Alice', age: 30 }, UserSchema);

if (res.ok) {
  console.log(res.value.name); // "Alice"
} else {
  console.error(res.error.message);
}

Standard Schema compatibility

Works with any library that implements the Standard Schema spec:

• Valibot
• Zod
• ArkType
• TypeBox

validate() signature

function validate<T>(
  value: unknown,
  schema: StandardSchemaV1<unknown, T>
): Promise<Result<T>>

Supported schema libraries

Any library implementing Standard Schema v1:

// Zod
import { z } from 'zod';
const schema = z.object({ name: z.string() });

// Valibot
import * as v from 'valibot';
const schema = v.object({ name: v.string() });

// ArkType
import { type } from 'arktype';
const schema = type({ name: 'string' });

// All work identically with validate()
const result = await validate({ name: 'Alice' }, schema);

Error on failure

Returns { ok: false, error: ValidationError }. The ValidationError.cause contains the raw schema issues:

const result = await validate(42, stringSchema);
if (!result.ok) {
  console.log(result.error.code); // 'validation.failed'
  console.log(result.error.cause); // schema-specific issues array
}

Using validate() standalone

call() uses validate() internally when a schema option is provided. You can also use it directly for any data validation that doesn't involve the LLM:

// Validate webhook payload
const body = await request.json();
const payload = await validate(body, WebhookSchema);
if (!payload.ok) return Response.json({ error: 'Invalid payload' }, { status: 400 });

See also

• call() — schema option uses validate() internally
• tool() — tool input is validated with validate()
• Error Types — ValidationError