/custom-field-type

name: webiny-api-cms-custom-field-type
description: >
  How to implement a custom CMS field type that integrates with the model builder's
  fluent API. Covers extending DataFieldBuilder, composing validator interfaces,
  creating a FieldTypeFactory, registering via DI, and module augmentation for
  TypeScript autocomplete on the fields() registry.

Custom CMS Field Type

TL;DR

A custom field type is a class that extends `DataFieldBuilder<"yourType">`, paired with a factory class implementing `FieldType.Factory`. Register the factory with `container.register(YourFieldType)`. Add a module augmentation on `"webiny/api/cms/model"` so the `fields` registry method gets TypeScript autocomplete.

When to Use This

Use a custom field type when:

• You need a field with a storage format or validation logic not covered by the built-in types (`text`, `number`, `boolean`, `datetime`, `file`, `ref`, `object`, `richText`, `longText`, `json`, `dynamicZone`)
• You want to expose a fluent builder API (e.g., `fields.slug()`, `fields.color()`) in `ModelFactory` implementations

Field Type Structure

A custom field type consists of three parts:

1. **Builder interface** — extends `DataFieldBuilder<"type">` plus `FieldTypeValidator.*` types 2. **Builder class** — implements the interface, calls `this.validation()` for each validator 3. **Factory class** — implements `FieldType.Factory`, creates builder instances

As a standalone extension (not part of a larger feature), the directory layout is:

extensions/
└── SlugFieldType/
    ├── SlugFieldType.ts     # builder interface, builder class, factory class
    └── feature.ts           # createFeature — registers the factory into the DI container

`feature.ts`:

// extensions/SlugFieldType/feature.ts
import { createFeature } from "webiny/api";
import { SlugFieldType } from "./SlugFieldType.js";

export const SlugFieldTypeFeature = createFeature({
  name: "SlugFieldType",
  register(container) {
    container.register(SlugFieldType);
  }
});

Register in the API entry point:

// api/Extension.ts
import { createFeature } from "webiny/api";
import { SlugFieldTypeFeature } from "~/extensions/SlugFieldType/feature.js";

export const Extension = createFeature({
  name: "MyExtension",
  register(container) {
    SlugFieldTypeFeature.register(container);
  }
});

Complete Example

// extensions/SlugFieldType/SlugFieldType.ts
import { DataFieldBuilder, FieldType } from "webiny/api/cms/model";
import type { FieldTypeValidator } from "webiny/api/cms/model";

// 1. Builder interface — extends DataFieldBuilder + desired FieldTypeValidator types
export interface ISlugFieldBuilder
  extends
    DataFieldBuilder<"slug">,
    FieldTypeValidator.Required,
    FieldTypeValidator.Pattern,
    FieldTypeValidator.Unique {}

// 2. Module augmentation — adds fields.slug() to the registry
declare module "webiny/api/cms/model" {
  interface IFieldBuilderRegistry {
    slug(): ISlugFieldBuilder;
  }

  interface IFieldRendererRegistry {
    myCustomRenderer: {
      fieldType: "text" | "number";
      settings: undefined;
    };
  }
}

// 3. Builder class — implements each validator method via this.validation()
class SlugFieldBuilder extends DataFieldBuilder<"slug"> implements ISlugFieldBuilder {
  constructor() {
    super("slug");
  }

  required(message?: string): this {
    return this.validation({
      name: "required",
      message: message || "Value is required.",
      settings: {}
    });
  }

  pattern(regex: string, flags = "", message?: string): this {
    return this.validation({
      name: "pattern",
      message: message || "Invalid value.",
      settings: { preset: "custom", regex, flags }
    });
  }

  unique(message?: string): this {
    return this.validation({
      name: "unique",
      message: message || "Value must be unique.",
      settings: {}
    });
  }
}

// 4. Factory class — implements FieldType.Factory
class SlugFieldTypeFactory implements FieldType.Factory {
  readonly type = "slug";

  create(): ISlugFieldBuilder {
    return new SlugFieldBuilder();
  }
}

// 5. Export as a FieldType implementation
export const SlugFieldType = FieldType.createImplementation({
  implementation: SlugFieldTypeFactory,
  dependencies: []
});

Using the Custom Field in a Model

After registration, `fields.slug()` is available in any `ModelFactory` implementation:

import { ModelFactory } from "webiny/api/cms/model";

class ProductModelImpl implements ModelFactory.Interface {
  async execute(builder: ModelFactory.Builder) {
    return [
      builder
        .public({ modelId: "product", name: "Product", group: "ungrouped" })
        .fields(fields => ({
          name: fields.text().label("Name").required(),
          slug: fields
            .slug()
            .label("Slug")
            .required("Slug is required.")
            .unique()
            .pattern("^[a-z0-9-]+$", "", "Only lowercase letters, numbers, and hyphens.")
        }))
        .layout([["name", "slug"]])
        .titleFieldId("name")
        .singularApiName("Product")
        .pluralApiName("Products")
    ];
  }
}

DataFieldBuilder API

All methods return `this` for chaining.

| Method | Description | | --------------------------- | --------------------------------------------- | | `label(text)` | Field label shown in the Admin editor | | `help(text)` | Help text shown below the field | | `description(text)` | Field description | | `fieldId(id)` | Override the auto-derived field ID | | `storageId(id)` | Override the storage identifier | | `placeholder(text)` | Placeholder text for the input | | `defaultValue(value)` | Default value for new entries | | `list()` | Make th