vee-validate 4.15.1

Form validation for Vue 3. Facts below come from the prepared source (dist/vee-validate.d.ts, dist/vee-validate.mjs, package.json) and official docs at https://vee-validate.logaretm.com/v4/.

Environment

Package vee-validate@4.15.1 (package.json:3). Requires vue ^3.4.26 as peer (package.json:42).
ESM + CJS, sideEffects: false, single entry vee-validate (package.json:11-26).
v4 supports Vue 3 only. Vue 2 needs vee-validate 2.x/3.x (README:69-72).
Schema adapters live in separate packages: @vee-validate/yup, @vee-validate/zod, @vee-validate/valibot; global rules in @vee-validate/rules; messages in @vee-validate/i18n.

Two API styles

Composition API (preferred for new code). useForm + defineField + handleSubmit:

<script setup>
import { useForm } from 'vee-validate';

function required(value) {
  return value ? true : 'This field is required';
}

const { defineField, handleSubmit, errors } = useForm({
  validationSchema: { field: required },
});

const [field, fieldProps] = defineField('field');

const onSubmit = handleSubmit(values => {
  console.log(values);
});
</script>

<template>
  <form @submit="onSubmit">
    <input v-model="field" v-bind="fieldProps" />
    <span>{{ errors.field }}</span>
    <button>Submit</button>
  </form>
</template>

Source: README:84-118, https://vee-validate.logaretm.com/v4/guide/composition-api/getting-started/

Declarative components. Form + Field with scoped slots:

<script setup>
import { Field, Form } from 'vee-validate';

function required(value) {
  return value ? true : 'This field is required';
}

function onSubmit(values) {
  console.log(values);
}
</script>

<template>
  <Form v-slot="{ errors }" @submit="onSubmit">
    <Field name="field" :rules="required" />
    <span>{{ errors.field }}</span>
    <button>Submit</button>
  </Form>
</template>

Source: README:122-153, https://vee-validate.logaretm.com/v4/guide/components/handling-forms/

Core rules

Bind fields with defineField(path, config?). It returns [model, props]; spread the props with v-bind and the model with v-model (dist/vee-validate.d.ts:443, https://vee-validate.logaretm.com/v4/api/use-form/#definefield).
Never write directly to values.field; use the defineField model, setFieldValue, or useSetFieldValue.
useFieldModel, defineComponentBinds, and defineInputBinds are deprecated in favor of defineField (dist/vee-validate.d.ts:444-459).
Show errors only after interaction, e.g. v-if="errorMessage && meta.touched", to avoid aggressive validation UX (https://vee-validate.logaretm.com/v4/guide/best-practices/#avoiding-aggressive-validation).
For TypeScript, wrap yup/zod/valibot schemas with toTypedSchema from the matching @vee-validate/* package. Passing a raw schema without it fails with "No such validator 'VVTypedSchema' exists" (https://vee-validate.logaretm.com/v4/guide/composition-api/typed-schema/, https://github.com/logaretm/vee-validate/discussions/4819).
useField inside a custom component must not sync its v-model by default (syncVModel defaults to false, breaking change in 4.10.0). Opt in per field with syncVModel: true or a model prop name string (dist/vee-validate.mjs:1862).
Field names are paths. Dots nest objects, [0] indexes arrays; wrap the name in brackets, e.g. [user.name], to treat dots as literal (https://vee-validate.logaretm.com/v4/guide/composition-api/nested-objects-and-arrays/).
The errors object is always flat: reference the exact path string used as the field name, brackets included (https://vee-validate.logaretm.com/v4/guide/composition-api/nested-objects-and-arrays/).
Iterate array fields with fields from useFieldArray and key v-for by entry.key (a stable id, never the index) (https://vee-validate.logaretm.com/v4/guide/composition-api/nested-objects-and-arrays/).
Pass reactive field names as getters (useField(() => props.name)) so vee-validate tracks name changes (https://vee-validate.logaretm.com/v4/guide/composition-api/caveats/).
Keep schemas non-reactive: declare them outside ref/reactive or wrap with markRaw to avoid deep reactivity overhead (https://vee-validate.logaretm.com/v4/guide/best-practices/#reactive-schemas).
handleSubmit.withControlled(cb) submits only fields registered with useField/defineField (dist/vee-validate.d.ts:430-432); note typed schemas can still surface all initial values (open issue: https://github.com/logaretm/vee-validate/issues/4960).

Validation modes

Global defaults: validateOnBlur: true, validateOnChange: true, validateOnInput: false, validateOnModelUpdate: true, bails: true. Change globally with configure(); note these four trigger flags only apply to the <Field> component, not useField (https://vee-validate.logaretm.com/v4/api/configuration/). To validate only on submit, disable input/change/blur triggers per field in defineField config or globally (https://github.com/logaretm/vee-validate/discussions/4903).

References

Composition API: useForm, defineField, useField, useFieldArray, state and setter composables, form context.
Components: Form, Field, FieldArray, ErrorMessage props, slots, rendering, v-model rules.
Validation: validator functions, object schemas, typed schemas, global rules, i18n, standalone validate utils.
API surface: every runtime export and notable type, cited to dist/vee-validate.d.ts.
Version changes: API additions, breaking changes, and deprecations from 4.9.0 to 4.15.1.
Pitfalls: composition caveats, nested path rules, array fields, known open issues.