Webiny Api Cms Custom Field Type

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.

Protected Methods (for use inside validator implementations only)

A CmsModelFieldValidation has the shape:

{
  name: string; // validator name (e.g., "required", "minLength", "pattern")
  message: string; // error message shown to the user
  settings: Record<string, any>; // validator-specific config
}

Available Validators

Import via import type { FieldTypeValidator } from "webiny/api/cms/model" and extend your builder interface with them. Each type adds one method to your interface:

When implementing a validator method in the builder class, call this.validation() with the appropriate name and settings. For ListMinLength/ListMaxLength, call this.listValidation() instead. The settings shapes:

Key Rules

1. type string must be unique — the factory's readonly type must not collide with any built-in type (text, number, boolean, datetime, file, ref, object, richText, longText, json, dynamicZone) or other custom types.
2. Module augmentation target — augment "webiny/api/cms/model" using namespace FieldBuilderRegistry { interface Interface { yourType(): IYourFieldBuilder; } }.
3. validation() is protected — never call it from outside the builder class. Expose validators as named methods on the interface (e.g., required(), minLength()).
4. dependencies: [] — field type factories have no DI dependencies; always pass an empty array.
5. Registration order — register custom FieldType implementations before FieldBuilderRegistry is resolved (i.e., in the same register() call or before it runs). The registry collects all FieldType instances at construction time.

Related Skills

• webiny-api-cms-content-models — Using the model builder's fluent API to define CMS models
• webiny-api-cms-catalog — Full catalog of CMS abstractions including ModelFactory, FieldType, DataFieldBuilder
• webiny-dependency-injection — The createImplementation pattern and DI scoping