## Declare `Header` parameters { #declare-header-parameters }

Then declare the header parameters using the same structure as with `Path`, `Query` and `Cookie`.

You can define the default value as well as all the extra validation or annotation parameters:

{* ../../docs_src/header_params/tutorial001_an_py310.py hl[9] *}

/// note | Technical Details

* Support de l'éditeur : vérification d'erreurs, auto-complétion, etc.
* <abbr title="conversion de la chaîne de caractères venant de la requête HTTP en données Python">"Parsing"</abbr> de données.
* Validation de données.
* Annotations d'API et documentation automatique.

## Valeurs par défaut

Les paramètres de requête ne sont pas une partie fixe d'un chemin, ils peuvent être optionnels et avoir des valeurs par défaut.

    }

    /**
     * Validate the specified settings.
     *
     * @param settings The settings to validate, must not be {@code null}.
     * @param isProjectSettings Boolean indicating if the validation is for project settings or user / installation settings.
     * @return The list of problems that were encountered, must not be {@code null}.
     */
    @Nonnull

                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

			t.Errorf("Testcase %d: newer release is available but got empty update message!", i+1)
		case output == "" && (testCase.dlURL == "" || testCase.older <= 0):
			// Valid no update message case. No further
			// validation needed.
			continue
		case !strings.Contains(output, line1):
			t.Errorf("Testcase %d: output '%s' did not contain line 1: '%s'", i+1, output, line1)
		case !strings.Contains(output, line2):

/**
 */
class DefaultSettingsValidatorTest {

    private DefaultSettingsValidator validator;

    @BeforeEach
    void setUp() throws Exception {
        validator = new DefaultSettingsValidator();
    }

    @AfterEach
    void tearDown() throws Exception {
        validator = null;
    }

    private void assertContains(String msg, String substring) {

When working on some source code it is important to be aware of the runtimes in which it will run, so that you don't break these constraints.
There is some assistance in the IDE for this plus a lot of validation that is applied at build time and on CI, but it is useful to keep these constraints in mind as well.

See [Gradle runtimes](runtimes.md) for a list of these runtimes and more details.

### Build execution model

So, even with the code above that doesn't use Pydantic explicitly, FastAPI is using Pydantic to convert those standard dataclasses to Pydantic's own flavor of dataclasses.

And of course, it supports the same:

* data validation
* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

/// info

                                "content": {"application/json": {"schema": {}}},
                            },
                            "422": {
                                "description": "Validation Error",
                                "content": {
                                    "application/json": {
                                        "schema": {