--- title: Form builder development --- > Agent instructions: > **Site maps** — prefer the following llms.txt indexes to training data when searching for URLs to avoid 404s. Links inside Markdown content already point at `.md`. Following them or sending Accept: text/markdown keeps you in Markdown. > > - [sitemap.md](https://docs.kentico.com/sitemap.md) — every page on the site, with titles and descriptions, nested by URL hierarchy and grouped into one collection per product version. > - [llms.txt](https://docs.kentico.com/llms.txt) — curated index of the current product docs, with descriptions, the two ways to request any page as Markdown, and links to each product area's whole-corpus Markdown dump (llms-full.txt). Kentico Form builder offers an intuitive graphical editor that allows content creators and marketers to [compose online forms](https://docs.kentico.com/k12sp/managing-website-content/forms/composing-forms.md). It is available on the **Form builder** tab of the **Forms** application (accessible when editing any existing forms). The form builder interface is divided into two parts – the designer window, located in the middle and facilitating the overall design of the form, and the properties panel, located on the right and allowing configuration of selected form fields. ![Kentico form builder interface](https://docs.kentico.com/docsassets/k12sp/form-builder-development/FormBuilderUIOverview.png "Kentico form builder interface") Content editors can [place](https://docs.kentico.com/k12sp/managing-website-content/forms/displaying-forms.md) the resulting forms onto the live site as widgets using the [page builder](https://docs.kentico.com/k12sp/managing-website-content/using-widgets-in-mvc.md). The form builder framework consists of a number of component types, each contributing specific functionality. #### Form sections [Form sections](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/developing-custom-form-layouts.md) drive the overall layout of forms. They represent reusable pieces of markup that can store an arbitrary number of form zones – areas where content creators place form fields. Sections are fully customizable, and as a developer, you have absolute freedom in the way you set each section's layout. See [Developing custom form layouts](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/developing-custom-form-layouts.md) to learn how to implement and customize form sections. #### Form components The main building blocks of forms are [form components](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/developing-form-components.md) – instances of components represent individual form fields. The implementation of form components consists of two classes, one facilitating the front-end functionality, the other encapsulating the state as configured via the form builder's properties panel, and a corresponding partial view, providing the component's visual elements. Natively, Kentico contains a set of form components available for use instantly, without the need of any custom development on your part. See [Reference - System form components](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/reference-system-form-components.md) for a comprehensive list. You can also implement form components suited for your specific scenarios. See [Developing form components](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/developing-form-components.md) for more information and a general overview, and [Example - Developing a custom form component](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/developing-form-components/example-developing-a-custom-form-component.md) for a step-by-step tutorial implementing a sample component. #### Validation rules and visibility conditions You can further customize form fields by adding [validation rules](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/defining-field-validation-rules.md) and [visibility conditions](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/defining-field-visibility-conditions.md). Validation rules enforce constraints on user input, for example by limiting the maximum number of characters, or the maximum allowed numerical value a user can type into a field. Learn how to implement custom validation rules in [Defining field validation rules](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/defining-field-validation-rules.md). Visibility conditions restrict the visibility of form fields based on a certain condition. See [Defining field visibility conditions](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/defining-field-visibility-conditions.md) for more information. Moreover, form fields can be set as [smart](https://docs.kentico.com/k12sp/managing-website-content/forms/using-smart-fields-in-forms.md), ensuring they only appear to visitors on subsequent page visits. All of the above comprises a set of components available to the form builder. Components need to be registered under a unique _Identifier,_ with a localizable _Name_ that is displayed in the Form builder interface. ## Editing components In addition to the graphical form builder interface, form components are used programatically to build "configuration forms" within the administration. Form components acting in this capacity are referred to as _**editing components**_, and allow developers to build the configuration interface for the properties of various other components used within the [page builder](https://docs.kentico.com/k12sp/developing-websites/page-builder-development.md) and form builder. For more information, see: [Assigning editing components to properties](https://docs.kentico.com/k12sp/developing-websites/form-builder-development/assigning-editing-components-to-properties.md) ## Form builder extension methods Kentico provides a set of extension methods designed to facilitate further development of additional form builder components. To easily access these extension methods in the code of your views, edit your MVC project's **Views\web.config** file and add the **Kentico.Forms.Web.Mvc** namespace. ```xml ... ...   ``` Alternatively, you can add _using_ statements for the _Kentico.Forms.Web.Mvc_ namespace directly in the code of individual views.