---
title: LanguageModelSession.ToolCallError
framework: foundationmodels
role: symbol
role_heading: Structure
path: foundationmodels/languagemodelsession/toolcallerror
---

# LanguageModelSession.ToolCallError

An error that occurs while a system language model is calling a tool.

## Declaration

```swift
struct ToolCallError
```

## Mentioned in

Expanding generation with tool calling

## Topics

### Creating a tool call error

- [init(tool:underlyingError:)](foundationmodels/languagemodelsession/toolcallerror/init(tool:underlyingerror:).md)

### Getting the tool

- [tool](foundationmodels/languagemodelsession/toolcallerror/tool.md)

### Getting the error description

- [errorDescription](foundationmodels/languagemodelsession/toolcallerror/errordescription.md)

### Getting the underlying error

- [underlyingError](foundationmodels/languagemodelsession/toolcallerror/underlyingerror.md)

## Relationships

### Conforms To

- [Error](swift/error.md)
- [LocalizedError](foundation/localizederror.md)
- [Sendable](swift/sendable.md)
- [SendableMetatype](swift/sendablemetatype.md)

## See Also

### Errors

- [LanguageModelSession.Error](foundationmodels/languagemodelsession/error.md)
- [LanguageModelSession.GenerationError](foundationmodels/languagemodelsession/generationerror.md)