Tool Calling

Enable on-device LLMs to invoke your Dart functions by registering typed tool definitions. The SDK handles argument parsing, execution, and result formatting automatically.

Tool calling uses the RunAnywhereTools class, not RunAnywhere. All tool registration and generation methods live on RunAnywhereTools.

Basic Usage

import 'package:runanywhere/runanywhere.dart';

// 1. Clear any previously registered tools
RunAnywhereTools.clearTools();

// 2. Register a tool
RunAnywhereTools.registerTool(
  const ToolDefinition(
    name: 'get_weather',
    description: 'Gets the current weather for a location',
    parameters: [
      ToolParameter(
        name: 'location',
        type: ToolParameterType.string,
        description: 'City name, e.g. "San Francisco"',
      ),
    ],
    category: 'Utility',
  ),
  _fetchWeather,
);

// 3. Generate with tools
final result = await RunAnywhereTools.generateWithTools(
  'What is the weather in San Francisco?',
  options: const ToolCallingOptions(
    maxToolCalls: 3,
    autoExecute: true,
    temperature: 0.7,
    maxTokens: 512,
  ),
);

print(result.text);        // "The weather in San Francisco is 72°F and sunny."
print(result.toolCalls);   // [ToolCall(toolName: 'get_weather', ...)]
print(result.toolResults); // [ToolResult(success: true, ...)]

Setup

1. Import the SDK

import 'package:runanywhere/runanywhere.dart';

2. Define Tool Executors

Every tool executor must match the signature Future<Map<String, ToolValue>> Function(Map<String, ToolValue>):

Future<Map<String, ToolValue>> _fetchWeather(
  Map<String, ToolValue> args,
) async {
  final location = args['location']?.stringValue ?? 'Unknown';

  // Call your weather service, local DB, or any async Dart code
  return {
    'temperature': NumberToolValue(72.0),
    'condition': StringToolValue('sunny'),
    'location': StringToolValue(location),
  };
}

3. Register Tools

RunAnywhereTools.clearTools();

RunAnywhereTools.registerTool(
  const ToolDefinition(
    name: 'get_weather',
    description: 'Gets the current weather for a location',
    parameters: [
      ToolParameter(
        name: 'location',
        type: ToolParameterType.string,
        description: 'City name, e.g. "San Francisco"',
      ),
    ],
    category: 'Utility',
  ),
  _fetchWeather,
);

Always call RunAnywhereTools.clearTools() before registering tools to avoid duplicates when hot-reloading during development.

API Reference

RunAnywhereTools

Method	Return Type	Description
`registerTool(definition, executor)`	`void`	Register a tool with its definition and executor function
`clearTools()`	`void`	Remove all registered tools
`generateWithTools(prompt, {options})`	`Future<ToolCallingResult>`	Run the full orchestration loop: generate → parse → execute → repeat

ToolDefinition

Property	Type	Required	Description
`name`	`String`	Yes	Unique identifier for the tool
`description`	`String`	Yes	Human-readable description the LLM uses to decide when to call the tool
`parameters`	`List<ToolParameter>`	Yes	Typed parameter definitions
`category`	`String`	No	Logical grouping (e.g. `'Utility'`, `'Data'`)

ToolParameter

Property	Type	Required	Description
`name`	`String`	Yes	Parameter name
`type`	`ToolParameterType`	Yes	One of `string`, `number`, `boolean`, `object`, `array`
`description`	`String`	Yes	What this parameter represents

ToolCallingOptions

Property	Type	Default	Description
`maxToolCalls`	`int`	`5`	Maximum tool invocations per generation
`autoExecute`	`bool`	`true`	Automatically execute tool calls and feed results back to the LLM
`temperature`	`double`	`0.8`	Sampling temperature (0.0–2.0)
`maxTokens`	`int`	`256`	Maximum tokens in the final response

ToolCallingResult

Property	Type	Description
`text`	`String`	Final text response after all tool calls complete
`toolCalls`	`List<ToolCall>`	Every tool call the LLM requested; each has `toolName` (`String`) and `arguments` (`Map<String, ToolValue>`)
`toolResults`	`List<ToolResult>`	Execution results; each has `result` (`Map<String, ToolValue>?`), `error` (`String?`), and `success` (`bool`)

ToolValue Types

ToolValue is a Dart 3 sealed class. Create instances with the concrete subtypes and read values with the stringValue getter or pattern matching.

Subtype	Constructor	Description
`StringToolValue`	`StringToolValue('hello')`	String value
`NumberToolValue`	`NumberToolValue(42.0)`	Numeric value (double)
`BoolToolValue`	`BoolToolValue(true)`	Boolean value
`NullToolValue`	`NullToolValue()`	Explicit null
`ArrayToolValue`	`ArrayToolValue()`	Array / list value
`ObjectToolValue`	`ObjectToolValue()`	Nested object value

Access any value as a string via the .stringValue getter:

final temp = args['temperature'];
print(temp?.stringValue); // "72.0"

Pattern Matching (Dart 3)

Use exhaustive switch expressions on the sealed class:

String formatToolValue(ToolValue value) {
  return switch (value) {
    StringToolValue sv => sv.stringValue,
    NumberToolValue nv => nv.value.toString(),
    BoolToolValue bv   => bv.value.toString(),
    NullToolValue()    => 'null',
    ArrayToolValue()   => '[array]',
    ObjectToolValue()  => '{object}',
  };
}

Examples

Weather Tool

Future<Map<String, ToolValue>> _fetchWeather(
  Map<String, ToolValue> args,
) async {
  final location = args['location']?.stringValue ?? 'Unknown';
  // Simulate API call
  return {
    'temperature': NumberToolValue(72.0),
    'condition': StringToolValue('sunny'),
    'location': StringToolValue(location),
  };
}

RunAnywhereTools.registerTool(
  const ToolDefinition(
    name: 'get_weather',
    description: 'Gets the current weather for a location',
    parameters: [
      ToolParameter(
        name: 'location',
        type: ToolParameterType.string,
        description: 'City name',
      ),
    ],
    category: 'Utility',
  ),
  _fetchWeather,
);

Calculator Tool

Future<Map<String, ToolValue>> _calculate(
  Map<String, ToolValue> args,
) async {
  final a = (args['a'] as NumberToolValue?)?.value ?? 0;
  final b = (args['b'] as NumberToolValue?)?.value ?? 0;
  final op = args['operation']?.stringValue ?? 'add';

  final result = switch (op) {
    'add'      => a + b,
    'subtract' => a - b,
    'multiply' => a * b,
    'divide'   => b != 0 ? a / b : double.nan,
    _          => double.nan,
  };

  return {'result': NumberToolValue(result)};
}

RunAnywhereTools.registerTool(
  const ToolDefinition(
    name: 'calculate',
    description: 'Performs basic arithmetic on two numbers',
    parameters: [
      ToolParameter(
        name: 'a',
        type: ToolParameterType.number,
        description: 'First operand',
      ),
      ToolParameter(
        name: 'b',
        type: ToolParameterType.number,
        description: 'Second operand',
      ),
      ToolParameter(
        name: 'operation',
        type: ToolParameterType.string,
        description: 'One of: add, subtract, multiply, divide',
      ),
    ],
    category: 'Math',
  ),
  _calculate,
);

Current Time Tool

Future<Map<String, ToolValue>> _getTime(
  Map<String, ToolValue> args,
) async {
  final timezone = args['timezone']?.stringValue ?? 'UTC';
  final now = DateTime.now().toUtc();

  return {
    'time': StringToolValue(now.toIso8601String()),
    'timezone': StringToolValue(timezone),
  };
}

RunAnywhereTools.registerTool(
  const ToolDefinition(
    name: 'get_current_time',
    description: 'Returns the current date and time',
    parameters: [
      ToolParameter(
        name: 'timezone',
        type: ToolParameterType.string,
        description: 'IANA timezone, e.g. "America/New_York"',
      ),
    ],
    category: 'Utility',
  ),
  _getTime,
);

A full-screen widget that registers weather, calculator, and time tools, then runs a multi-tool conversation:

import 'package:flutter/material.dart';
import 'package:runanywhere/runanywhere.dart';

class ToolCallingScreen extends StatefulWidget {
  const ToolCallingScreen({super.key});

  @override
  State<ToolCallingScreen> createState() => _ToolCallingScreenState();
}

class _ToolCallingScreenState extends State<ToolCallingScreen> {
  String _response = '';
  List<String> _toolLog = [];
  bool _isLoading = false;

  @override
  void initState() {
    super.initState();
    _registerTools();
  }

  void _registerTools() {
    RunAnywhereTools.clearTools();

    RunAnywhereTools.registerTool(
      const ToolDefinition(
        name: 'get_weather',
        description: 'Gets the current weather for a location',
        parameters: [
          ToolParameter(
            name: 'location',
            type: ToolParameterType.string,
            description: 'City name, e.g. "San Francisco"',
          ),
        ],
        category: 'Utility',
      ),
      _fetchWeather,
    );

    RunAnywhereTools.registerTool(
      const ToolDefinition(
        name: 'calculate',
        description: 'Performs basic arithmetic on two numbers',
        parameters: [
          ToolParameter(
            name: 'a',
            type: ToolParameterType.number,
            description: 'First operand',
          ),
          ToolParameter(
            name: 'b',
            type: ToolParameterType.number,
            description: 'Second operand',
          ),
          ToolParameter(
            name: 'operation',
            type: ToolParameterType.string,
            description: 'One of: add, subtract, multiply, divide',
          ),
        ],
        category: 'Math',
      ),
      _calculate,
    );

    RunAnywhereTools.registerTool(
      const ToolDefinition(
        name: 'get_current_time',
        description: 'Returns the current date and time',
        parameters: [
          ToolParameter(
            name: 'timezone',
            type: ToolParameterType.string,
            description: 'IANA timezone, e.g. "America/New_York"',
          ),
        ],
        category: 'Utility',
      ),
      _getTime,
    );
  }

  Future<Map<String, ToolValue>> _fetchWeather(
    Map<String, ToolValue> args,
  ) async {
    final location = args['location']?.stringValue ?? 'Unknown';
    return {
      'temperature': NumberToolValue(72.0),
      'condition': StringToolValue('sunny'),
      'location': StringToolValue(location),
    };
  }

  Future<Map<String, ToolValue>> _calculate(
    Map<String, ToolValue> args,
  ) async {
    final a = (args['a'] as NumberToolValue?)?.value ?? 0;
    final b = (args['b'] as NumberToolValue?)?.value ?? 0;
    final op = args['operation']?.stringValue ?? 'add';

    final result = switch (op) {
      'add'      => a + b,
      'subtract' => a - b,
      'multiply' => a * b,
      'divide'   => b != 0 ? a / b : double.nan,
      _          => double.nan,
    };

    return {'result': NumberToolValue(result)};
  }

  Future<Map<String, ToolValue>> _getTime(
    Map<String, ToolValue> args,
  ) async {
    final timezone = args['timezone']?.stringValue ?? 'UTC';
    final now = DateTime.now().toUtc();
    return {
      'time': StringToolValue(now.toIso8601String()),
      'timezone': StringToolValue(timezone),
    };
  }

  Future<void> _runPrompt(String prompt) async {
    setState(() {
      _isLoading = true;
      _response = '';
      _toolLog = [];
    });

    try {
      final result = await RunAnywhereTools.generateWithTools(
        prompt,
        options: const ToolCallingOptions(
          maxToolCalls: 3,
          autoExecute: true,
          temperature: 0.7,
          maxTokens: 512,
        ),
      );

      setState(() {
        _response = result.text;
        _toolLog = [
          for (final call in result.toolCalls)
            '→ ${call.toolName}(${call.arguments.map(
              (k, v) => MapEntry(k, v.stringValue),
            )})',
          for (final res in result.toolResults)
            res.success
                ? '✓ ${res.result}'
                : '✗ ${res.error}',
        ];
      });
    } catch (e) {
      setState(() => _response = 'Error: $e');
    } finally {
      setState(() => _isLoading = false);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Tool Calling Demo')),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Wrap(
              spacing: 8,
              runSpacing: 8,
              children: [
                ElevatedButton(
                  onPressed: _isLoading
                      ? null
                      : () => _runPrompt(
                            'What is the weather in San Francisco?',
                          ),
                  child: const Text('Weather'),
                ),
                ElevatedButton(
                  onPressed: _isLoading
                      ? null
                      : () => _runPrompt('What is 42 * 17?'),
                  child: const Text('Calculate'),
                ),
                ElevatedButton(
                  onPressed: _isLoading
                      ? null
                      : () => _runPrompt('What time is it in UTC?'),
                  child: const Text('Time'),
                ),
              ],
            ),
            const SizedBox(height: 16),
            if (_isLoading) const LinearProgressIndicator(),
            const SizedBox(height: 16),
            if (_toolLog.isNotEmpty) ...[
              Text(
                'Tool Activity',
                style: Theme.of(context).textTheme.titleSmall,
              ),
              const SizedBox(height: 4),
              for (final log in _toolLog)
                Padding(
                  padding: const EdgeInsets.symmetric(vertical: 2),
                  child: Text(log, style: const TextStyle(fontFamily: 'monospace', fontSize: 13)),
                ),
              const Divider(height: 24),
            ],
            if (_response.isNotEmpty)
              Expanded(
                child: SingleChildScrollView(
                  child: Text(_response, style: const TextStyle(fontSize: 16)),
                ),
              ),
          ],
        ),
      ),
    );
  }
}

Error Handling

Wrap generateWithTools in a try-catch and inspect individual ToolResult entries for per-tool errors:

try {
  final result = await RunAnywhereTools.generateWithTools(
    prompt,
    options: const ToolCallingOptions(maxToolCalls: 3, autoExecute: true),
  );

  for (final res in result.toolResults) {
    if (!res.success) {
      debugPrint('Tool failed: ${res.error}');
    }
  }
} on RunAnywhereException catch (e) {
  debugPrint('SDK error: ${e.message}');
} catch (e) {
  debugPrint('Unexpected error: $e');
}

If a tool executor throws, the SDK catches the exception and records it in the corresponding ToolResult.error field. The LLM receives the error message and can retry or respond gracefully.

Common Errors

Error	Cause	Fix
`ToolNotFound`	LLM requested an unregistered tool	Verify tool names match exactly
`MaxToolCallsExceeded`	Hit the `maxToolCalls` limit	Increase the limit or simplify the prompt
`ModelNotLoaded`	No LLM model loaded	Call `RunAnywhere.loadModel(...)` before generating
`InvalidArguments`	Argument types don’t match the definition	Check `ToolParameterType` in your `ToolDefinition`

LLM Generation

Text generation with metrics

Streaming

Stream tokens in real-time

System Prompts

Control LLM behavior with system prompts

Error Handling

SDK-wide error handling patterns

Getting Started

Swift SDK

Kotlin SDK

React Native SDK

Flutter SDK

Web SDK

Vibe Coding

Basic Usage

Setup

1. Import the SDK

2. Define Tool Executors

3. Register Tools

API Reference

RunAnywhereTools

ToolDefinition

ToolParameter

ToolCallingOptions

ToolCallingResult

ToolValue Types

Pattern Matching (Dart 3)

Examples

Weather Tool

Calculator Tool

Current Time Tool

Complete Flutter Widget

Error Handling

Common Errors

See Also

LLM Generation

Streaming

System Prompts

Error Handling

​Basic Usage

​Setup

​1. Import the SDK

​2. Define Tool Executors

​3. Register Tools

​API Reference

​RunAnywhereTools

​ToolDefinition

​ToolParameter

​ToolCallingOptions

​ToolCallingResult

​ToolValue Types

​Pattern Matching (Dart 3)

​Examples

​Weather Tool

​Calculator Tool

​Current Time Tool

​Complete Flutter Widget

​Error Handling

​Common Errors

​See Also

LLM Generation

Streaming

System Prompts

Error Handling

Basic Usage

Setup

1. Import the SDK

2. Define Tool Executors

3. Register Tools

API Reference

RunAnywhereTools

ToolDefinition

ToolParameter

ToolCallingOptions

ToolCallingResult

ToolValue Types

Pattern Matching (Dart 3)

Examples

Weather Tool

Calculator Tool

Current Time Tool

Complete Flutter Widget

Error Handling

Common Errors

See Also