Fields

Every field has a name and a type. The type decides what values it accepts; the options on this page narrow that further.

Field types

Type	Stores	Type-specific options
text	One line of text, or a list with hasMany	minLength, maxLength, hasMany, minRows, maxRows
textarea	Longer text	minLength, maxLength
number	A number, or a list with hasMany	min, max, integer, hasMany, minRows, maxRows
checkbox	true or false. Saved schemas call it boolean, which works as a name too.	none
date	A date-time in UTC to the millisecond, such as 2026-10-12T09:30:00Z, or a plain date like 2026-10-12 with dateOnly	dateOnly
email	An email address	none
url	An http or https URL	none
select	One of a fixed list of values, or several with multiple	options, multiple
radio	One of a fixed list of values	options
slug	Lowercase letters, digits and single hyphens, like my-first-post	from
code	Source code as text	language
point	A location as [longitude, latitude]	none
json	Any JSON value	none
relationship	A link to a document in another collection, or a list of links	relationTo, hasMany, maxDepth
join	Nothing: lists the documents that link here, on every read	collection, on, where, defaultLimit, defaultSort
group	An object of other fields	fields
array	A list of rows, each an object of other fields	fields, minRows, maxRows

relationship is covered in Relationships, and join in Joins and virtual fields.

A few details:

• select and radio options are plain values (["draft", "live"]) or labelled ones ([{"label": "Draft", "value": "draft"}]). Only the value is stored.
• A slug with from names a text field. When a document arrives without a slug, TachyonCMS makes one from that field: Tate Modern becomes tate-modern.
• A point can be searched by distance with the near filter.
• Inside a json field, null is an ordinary value, not a way to clear the field.

Options every field takes

Option	Does
required	The field must have a value.
default	The value to use when a new document doesn’t send one.
unique	No two documents in the collection may share a value. Deleted documents don’t count.
filterable	Builds a database index on the field, so filters and sorts on it stay fast.
label	A human name for the field.
admin	Hints for an editing screen. See Admin hints.
access	Who may read and write this field. See Access rules.
virtual	Read the value through a relationship instead of storing it. See Joins and virtual fields.

An example

This adds seven fields to posts, including a select, a list of text, a group and an array:

curl -X PUT localhost:3000/api/admin/collections/posts \
  -H "authorization: Bearer $TOKEN" \
  -H 'content-type: application/json' \
  -d '{"schema": {"slug": "posts", "fields": [
        {"name": "title", "type": "text", "required": true, "maxLength": 120},
        {"name": "publishedOn", "type": "date", "dateOnly": true},
        {"name": "summary", "type": "textarea"},
        {"name": "kind", "type": "select", "default": "article",
         "options": [{"label": "Article", "value": "article"}, {"label": "Note", "value": "note"}]},
        {"name": "tags", "type": "text", "hasMany": true, "maxRows": 5},
        {"name": "seo", "type": "group", "fields": [
          {"name": "title", "type": "text", "maxLength": 60},
          {"name": "description", "type": "textarea"}
        ]},
        {"name": "links", "type": "array", "fields": [
          {"name": "label", "type": "text", "required": true},
          {"name": "url", "type": "url", "required": true}
        ]}
      ]}}'

Create a post that fills them:

curl -X POST localhost:3000/api/posts \
  -H "authorization: Bearer $TOKEN" \
  -H 'content-type: application/json' \
  -d '{"title": "Shipping v0.1.0", "publishedOn": "2026-10-27", "kind": "article",
       "tags": ["release", "rust"],
       "seo": {"title": "TachyonCMS v0.1.0", "description": "The first release."},
       "links": [{"label": "Release notes", "url": "https://github.com/tachyon-cms/tachyoncms/releases/tag/v0.1.0"}]}'

{
  "createdAt": "2026-10-28T21:17:05.883493Z",
  "id": "01a1845f-afdb-75d9-af23-79cecf8ebabc",
  "kind": "article",
  "links": [
    {
      "label": "Release notes",
      "url": "https://github.com/tachyon-cms/tachyoncms/releases/tag/v0.1.0"
    }
  ],
  "publishedOn": "2026-10-27",
  "seo": {
    "description": "The first release.",
    "title": "TachyonCMS v0.1.0"
  },
  "status": "published",
  "tags": [
    "release",
    "rust"
  ],
  "title": "Shipping v0.1.0",
  "updatedAt": "2026-10-28T21:17:05.883493Z"
}

Validation errors

A document that doesn’t fit gets a 422 listing every problem at once. Each path points at the field, through groups (seo.title) and into list rows by position (links.0.url):

curl -X POST localhost:3000/api/posts \
  -H "authorization: Bearer $TOKEN" \
  -H 'content-type: application/json' \
  -d '{"title": "", "kind": "essay",
       "seo": {"title": "This search title is far too long to fit in sixty characters at all"},
       "links": [{"label": "Docs", "url": "not a url"}]}'

{
  "errors": [
    {
      "message": "is required",
      "path": "title"
    },
    {
      "message": "expected one of: article, note",
      "path": "kind"
    },
    {
      "message": "must be at most 60 characters",
      "path": "seo.title"
    },
    {
      "message": "expected an http or https URL",
      "path": "links.0.url"
    }
  ],
  "requestId": "01a1845f-afcb-7036-9452-7c91cfe02c2b",
  "status": 422,
  "title": "Validation failed",
  "type": "about:blank"
}

A unique value that’s already taken is a 422 on that field too:

{
  "errors": [
    {
      "message": "must be unique; another document already uses this value",
      "path": "slug"
    }
  ],
  "requestId": "01a18460-5b9a-744c-9fce-3e15fc4903b5",
  "status": 422,
  "title": "Validation failed",
  "type": "about:blank"
}

Updating: send only what changed

PATCH merges what you send into the stored document:

• A field inside a group changes on its own. Sending seo.title leaves seo.description as it was.
• A list (hasMany, array, a multiple select) is replaced whole.
• null clears a field, wherever it sits.

curl -X PATCH localhost:3000/api/posts/01a1845f-afdb-75d9-af23-79cecf8ebabc \
  -H "authorization: Bearer $TOKEN" \
  -H 'content-type: application/json' \
  -d '{"seo": {"title": "TachyonCMS 0.1.0 is out"}, "tags": null}'

{
  "createdAt": "2026-10-28T21:17:05.883493Z",
  "id": "01a1845f-afdb-75d9-af23-79cecf8ebabc",
  "kind": "article",
  "links": [
    {
      "label": "Release notes",
      "url": "https://github.com/tachyon-cms/tachyoncms/releases/tag/v0.1.0"
    }
  ],
  "publishedOn": "2026-10-27",
  "seo": {
    "description": "The first release.",
    "title": "TachyonCMS 0.1.0 is out"
  },
  "status": "published",
  "title": "Shipping v0.1.0",
  "updatedAt": "2026-10-28T21:17:05.902129Z"
}

seo.description kept its value, and tags is gone.

Layout fields

Three types arrange fields on an editing screen without changing the shape of the data. Their fields are stored as if they sat directly in the parent:

Type	Shows its fields	Options
row	side by side	fields
collapsible	in a section that can fold away, titled by its label	fields, initiallyCollapsed
tabs	in tabs, each {"label": "…", "fields": […]}	tabs

A tab with a name is the exception: it nests its fields under that name, like a group. Layout fields have no data, so they can’t carry access rules; put rules on the fields inside.

Admin hints

admin on any field holds hints for an editing screen. The API stores them and returns them with the schema, but doesn’t enforce them. v0.1.0 has no admin screen yet.

Hint	Value
description	Help text shown with the field.
placeholder	Placeholder text.
hidden	true to hide the field.
readOnly	true to show the field without letting people edit it.
position	main (the default) or sidebar.
width	A width such as 50% or 240px.
condition	Show the field only when another field matches: {"field": "kind", "equals": "note"}. The test is one of equals, notEquals, in or exists.