Field types

A field's type says what it holds and how it is checked. There is a type for every native form control, two types that hold other fields, and three display elements. Below you will learn what each one does.

Overview

Type	Value	Props
text, textarea, password, tel	a string
email, url	a string, checked by its format
number	a number
checkbox	true or false
date, time, datetime	an ISO string, like "2026-10-28"	output?
select, radio	the value of one option	options, valueType?
multiselect	the values of some options	options
file	a File, or a list with multiple	multiple?, accept?
heading, paragraph, divider	none: text between fields	text, level?
group	an object with a key for each field	fields
array	a list of values or of objects	of or fields

Each type also has a kind: string, number, boolean, date, array, file, object, or none for a display element. The kind decides which rules fit the field and what counts as empty. The built-in field types reference lists every type with its kind and props.

Anything more specific is a variant of one of these, or a type of your own. A star rating is a number with "ui": { "widget": "rating" }, and a colour picker is a text with the hexColor rule. Your renderer picks the component.

Text

text, textarea, password and tel hold a string. email and url do too, and check it with the email or url rule. A tel field takes any text: add a regex rule for the format you expect.

{
  "name": "phone",
  "type": "tel",
  "label": "Phone",
  "rules": [
    {
      "rule": "regex",
      "pattern": "^\\+?[0-9 ]{6,20}$",
      "message": "Use digits and spaces"
    }
  ]
}

Numbers

A number holds a number. An input element gives a string, like "5", so renderers turn it into a number before they set it. The adapters do that for you.

{
  "name": "quantity",
  "type": "number",
  "label": "Quantity",
  "default": 1,
  "rules": [{ "rule": "integer" }, { "rule": "minValue", "value": 1 }]
}

Checkboxes

A checkbox holds true or false. A required checkbox must be ticked, like one that accepts the terms. A checkbox nobody touched holds nothing, so give it "default": false when you need false in the output.

{
  "name": "acceptTerms",
  "type": "checkbox",
  "label": "I accept the terms",
  "required": { "message": "Please accept the terms" }
}

Dates and times

date, time and datetime hold ISO strings, like "2026-10-28", "14:30" and "2026-10-28T14:30", the values of the native inputs. The rules compare them as strings.

With "output": "date", a date or datetime outputs a Date instead, after every rule ran. Neither has a time zone, so the Date is in local time: a date is midnight of the picked day.

{
  "name": "birthDate",
  "type": "date",
  "label": "Birth date",
  "output": "date",
  "rules": [
    {
      "rule": "maxValue",
      "value": "2010-12-31",
      "message": "Pick a date in 2010 or before"
    }
  ]
}

Choices

A select or a radio holds the value of one of its options, and a multiselect holds a list of them. Options are { "value", "label" } objects: at least one, each value different, and all values of the same type.

{
  "name": "size",
  "type": "select",
  "label": "Size",
  "required": true,
  "options": [
    { "value": 1, "label": "Small" },
    { "value": 2, "label": "Medium" },
    { "value": 3, "label": "Large" }
  ]
}

• The options decide the kind. A select with number options has kind number: it rejects "1", and takes rules like minValue.
• A select without options, because they load from an API, takes any value of its valueType: "string", the default, or "number". With options, valueType is ignored.
• A required radio accepts any option, false included, so a yes or no radio can be required.
• A required multiselect needs at least one item. Add a minLength rule for more, like "pick at least two". Rules for the options' kind, like maxValue, run on each item.
• A checkbox group is a multiselect with "ui": { "widget": "checkboxes" }.

Files

A file holds a File, or a list of them with "multiple": true. accept takes MIME types separated by commas:

{
  "name": "photos",
  "type": "file",
  "label": "Photos",
  "multiple": true,
  "accept": "image/png,image/jpeg",
  "rules": [
    { "rule": "maxSize", "value": 5242880, "message": "Up to 5 MB each" },
    { "rule": "maxLength", "value": 4, "message": "Up to 4 photos" }
  ]
}

• A File only knows its MIME type, so extensions like .pdf and wildcards like image/* aren't accepted.
• With multiple, file rules like maxSize check each file, and maxLength limits how many there are.
• The schema reads the File global only while it parses, so the package also loads during server rendering.

Display elements

heading, paragraph and divider show text and lines between fields. They have no value, so they need no name, and take no default, required or rules.

{ "type": "heading", "text": "Delivery", "level": 3 }

A heading takes text and a level from 1 to 6, which defaults to 2. A paragraph takes text, as plain text: whether it renders markdown is up to your renderer. Their text can be an i18n key that your renderer translates.

Groups

A group holds other fields, and its value is an object with a key for each of them:

{
  "name": "address",
  "type": "group",
  "label": "Address",
  "fields": [
    { "name": "city", "type": "text", "required": true },
    { "name": "zip", "type": "text" }
  ]
}

The value is { address: { city, zip } }, and Formisch's path to the city is ['address', 'city']. A group is always there, and its fields decide what is required, so it takes no required or default. A name only has to be unique among the fields next to it.

Lists

An array holds a list. With of, it is a list of single values, like tags, and of is the field each item uses, without a name. With fields, it is a list of objects, like the lines of an order:

{
  "name": "lines",
  "type": "array",
  "label": "Order lines",
  "required": { "message": "Add at least one product" },
  "rules": [{ "rule": "maxLength", "value": 10 }],
  "fields": [
    { "name": "product", "type": "text", "required": true },
    { "name": "quantity", "type": "number", "default": 1 }
  ]
}

• Rules on a list, like minLength and maxLength, count its items, and a required list needs at least one.
• A new item starts with the defaults of its fields. The adapters' add() gives it to Formisch for you.
• Form rules, layouts and conditions name the field of an item with *: lines.*.quantity.

Display elements can go inside groups and lists too.

Next steps

Now that you know the field types, continue to validation rules to learn how to check their values.