> ## Documentation Index
> Fetch the complete documentation index at: https://fastql.vachagan.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom directives & field visibility

> Author schema directives, mark fields private or external, and customize enums.

## Custom directives

`@Directive` registers a directive definition; its arguments are derived from the
class's type hints. Apply it to types, fields, or arguments with `AppliedDirective`,
whose locations and argument types are validated at build time and rendered in the SDL.

```python theme={null}
from fastql import Argument, Directive, Field, Type
from fastql.types import AppliedDirective


@Directive(locations=["FIELD_DEFINITION", "OBJECT"], description="tag things")
class tag:
    name: str


@Type(directives=[AppliedDirective("tag", {"name": "obj"})])
class Widget:
    id: int

    @Field(directives=[AppliedDirective("tag", {"name": "fieldlevel"})])
    def label(self) -> str:
        return "w"
```

## Field visibility

`Field(private=True)` keeps a Python attribute off the GraphQL schema (still readable
by resolvers); `Field(external=True)` marks a field as federation-`@external`.

```python theme={null}
@Type
class User:
    handle: str
    secret: str = Field(private=True)        # excluded from the schema
```

## Enum customization

`enum_value` sets a member's GraphQL name, description, or deprecation.

```python theme={null}
from fastql import Enum, enum_value


@Enum
class Color:
    RED = "red"
    GREEN = enum_value("green", description="leafy", deprecation_reason="use RED")
    BLUE = enum_value("blue", name="AZURE")  # exposed as AZURE
```