> ## Documentation Index
> Fetch the complete documentation index at: https://docs.twenty.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Extending Objects

> Add fields to standard Twenty objects (Person, Company, …) or to objects from other apps using defineField.

Use `defineField()` to add a field to an object you don't own — a standard Twenty object like Person or Company, or an object shipped by another installed app. Unlike inline fields declared inside [`defineObject`](/developers/extend/apps/data/objects), standalone fields require an `objectUniversalIdentifier` to specify which object they extend.

```ts src/fields/company-loyalty-tier.field.ts theme={null}
import { defineField, FieldType } from 'twenty-sdk/define';

export default defineField({
  universalIdentifier: 'f2a1b3c4-d5e6-7890-abcd-ef1234567890',
  objectUniversalIdentifier: '701aecb9-eb1c-4d84-9d94-b954b231b64b', // Company object
  name: 'loyaltyTier',
  type: FieldType.SELECT,
  label: 'Loyalty Tier',
  icon: 'IconStar',
  options: [
    { value: 'BRONZE', label: 'Bronze', position: 0, color: 'orange' },
    { value: 'SILVER', label: 'Silver', position: 1, color: 'gray' },
    { value: 'GOLD', label: 'Gold', position: 2, color: 'yellow' },
  ],
});
```

## Key points

* `objectUniversalIdentifier` identifies the target object. For standard Twenty objects, import the constant from `twenty-sdk`:

  ```ts theme={null}
  import { STANDARD_OBJECT_UNIVERSAL_IDENTIFIERS } from 'twenty-sdk/define';

  // STANDARD_OBJECT_UNIVERSAL_IDENTIFIERS.company.universalIdentifier
  // STANDARD_OBJECT_UNIVERSAL_IDENTIFIERS.person.universalIdentifier
  // STANDARD_OBJECT_UNIVERSAL_IDENTIFIERS.opportunity.universalIdentifier
  // …
  ```

* When defining fields **inline inside `defineObject()`**, you do **not** need `objectUniversalIdentifier` — it's inherited from the parent object.

* `defineField()` is the only way to add fields to objects you didn't create with `defineObject()`.

* File location is up to you. The convention is `src/fields/<name>.field.ts`, but the SDK detects fields anywhere in `src/`.

* To add a tab to a standard page layout (e.g. the Task or Company detail page), use [`definePageLayoutTab`](/developers/extend/apps/layout/page-layouts#definepagelayouttab) with `STANDARD_PAGE_LAYOUT_UNIVERSAL_IDENTIFIERS` from `twenty-sdk/define`.

## Adding a relation to an existing object

To add a relation field (e.g. linking your custom object to a standard `Person`), use `defineField()` with `FieldType.RELATION`. The pattern is the same as for inline relations but with `objectUniversalIdentifier` set explicitly. See [Relations](/developers/extend/apps/data/relations) for the bidirectional pattern.