So, with that type declaration, **FastAPI** gives you automatic request <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>.

///

## Data validation { #data-validation }

But if you go to the browser at <a href="http://127.0.0.1:8000/items/foo" class="external-link" target="_blank">http://127.0.0.1:8000/items/foo</a>, you will see a nice HTTP error of:

```JSON
{

/// tip

If you have strict type checks in your editor, mypy, etc, you can declare the function return type as `Any`.

That way you tell the editor that you are intentionally returning anything. But FastAPI will still do the data documentation, validation, filtering, etc. with the `response_model`.

///

 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.admin.dict.protwords;

import org.lastaflute.web.validation.Required;
import org.lastaflute.web.validation.theme.conversion.ValidateTypeFailure;

/**
 * Form class for editing protected words dictionary entries in the admin interface.

 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.admin.plugin;

import org.lastaflute.web.ruts.multipart.MultipartFormFile;
import org.lastaflute.web.validation.Required;

import jakarta.validation.constraints.Size;

/**
 * Form for plugin installation through the admin web interface.
 * This class represents the form data structure for installing a plugin
 * via file upload through the admin UI.

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

import org.codelibs.fess.unit.UnitFessTestCase;
import org.codelibs.fess.validation.UriTypeValidator.ProtocolType;

import jakarta.validation.Constraint;
import jakarta.validation.Payload;

public class UriTypeTest extends UnitFessTestCase {

    // Test field with UriType annotation for WEB protocol
    @UriType(protocolType = ProtocolType.WEB)

```

</div>

/// tip

You can read more about it at <a href="https://12factor.net/config" class="external-link" target="_blank">The Twelve-Factor App: Config</a>.

///

## Types and Validation { #types-and-validation }

    }

    @Test
    @DisplayName("Should fail validation when not received")
    void testIsValidNotReceived() {
        // When
        boolean valid = response.isValid(mockContext, mockRequest);

        // Then
        assertFalse(valid);
    }

    @Test
    @DisplayName("Should fail validation when signing enforced but not enabled")

But by default, it all **"just works"**.

### Validation { #validation }

* Validation for most (or all?) Python **data types**, including:
    * JSON objects (`dict`).
    * JSON array (`list`) defining item types.
    * String (`str`) fields, defining min and max lengths.
    * Numbers (`int`, `float`) with min and max values, etc.

* Validation for more exotic types, like:
    * URL.
    * Email.

 */
package org.codelibs.fess.app.web.admin.storage;

import java.util.HashMap;
import java.util.Map;

import org.apache.logging.log4j.core.config.plugins.validation.constraints.Required;

import jakarta.validation.constraints.Size;

/**
 * Form class for handling tag operations in storage management.
 * This form represents tag data including path, name, and associated metadata.
 */

 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.app.web.admin.general;

import org.lastaflute.web.validation.Required;

import jakarta.validation.constraints.Size;

/**
 * The mail form for General settings.
 */
public class MailForm {

    /**
     * Default constructor.
     */
    public MailForm() {