firebase-js-sdk/docs-devsite/ai.functiondeclaration.md

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# FunctionDeclaration interface
Structured representation of a function declaration as defined by the [OpenAPI 3.0 specification](https://spec.openapis.org/oas/v3.0.3)<!-- -->. Included in this declaration are the function name and parameters. This `FunctionDeclaration` is a representation of a block of code that can be used as a Tool by the model and executed by the client.

<b>Signature:</b>

```typescript
export interface FunctionDeclaration 
```

## Properties

|  Property | Type | Description |
|  --- | --- | --- |
|  [description](./ai.functiondeclaration.md#functiondeclarationdescription) | string | Description and purpose of the function. Model uses it to decide how and whether to call the function. |
|  [functionReference](./ai.functiondeclaration.md#functiondeclarationfunctionreference) | Function | Reference to an actual function to call. Specifying this will cause the function to be called automatically when requested by the model. |
|  [name](./ai.functiondeclaration.md#functiondeclarationname) | string | The name of the function to call. Must start with a letter or an underscore. Must be a-z, A-Z, 0-9, or contain underscores and dashes, with a max length of 64. |
|  [parameters](./ai.functiondeclaration.md#functiondeclarationparameters) | [ObjectSchema](./ai.objectschema.md#objectschema_class) \| [ObjectSchemaRequest](./ai.objectschemarequest.md#objectschemarequest_interface) | Optional. Describes the parameters to this function in JSON Schema Object format. Reflects the Open API 3.03 Parameter Object. Parameter names are case-sensitive. For a function with no parameters, this can be left unset. |

## FunctionDeclaration.description

Description and purpose of the function. Model uses it to decide how and whether to call the function.

<b>Signature:</b>

```typescript
description: string;
```

## FunctionDeclaration.functionReference

Reference to an actual function to call. Specifying this will cause the function to be called automatically when requested by the model.

<b>Signature:</b>

```typescript
functionReference?: Function;
```

## FunctionDeclaration.name

The name of the function to call. Must start with a letter or an underscore. Must be a-z, A-Z, 0-9, or contain underscores and dashes, with a max length of 64.

<b>Signature:</b>

```typescript
name: string;
```

## FunctionDeclaration.parameters

Optional. Describes the parameters to this function in JSON Schema Object format. Reflects the Open API 3.03 Parameter Object. Parameter names are case-sensitive. For a function with no parameters, this can be left unset.

<b>Signature:</b>

```typescript
parameters?: ObjectSchema | ObjectSchemaRequest;
```