dart_agent_core is a mobile-first, local-first Dart library that implements an agentic loop with tool use, state persistence, and multi-turn memory. It connects to LLM APIs (OpenAI, Gemini, AWS Bedrock) and handles the orchestration layer — tool calling, streaming, context management, and sub-agent delegation — entirely in Dart, which makes it suitable for use in Flutter apps without a Python or Node.js backend.

Features #

• Multi-provider support: Unified LLMClient interface for OpenAI (Chat Completions & Responses API), Google Gemini, and Anthropic Claude via AWS Bedrock.
• Tool use: Wrap any Dart function as a tool with a JSON Schema definition. The agent dispatches calls, feeds results back, and loops until done. Tools can return AgentToolResult to carry multimodal content, metadata, or a stop signal.
• Multimodal input: UserMessage accepts text, images, audio, video, and documents as content parts. Model responses can include text, images, video, and audio.
• Stateful sessions: AgentState tracks conversation history, token usage, active skills, plan, and custom metadata. FileStateStorage persists state to disk as JSON.
• Streaming: runStream() yields StreamingEvents for model chunks, tool call requests/results, and retries — suitable for real-time UI updates in Flutter.
• Skill system: Define modular capabilities (Skill) with their own system prompts and tools. Skills can be always-on (forceActivate) or toggled dynamically by the agent at runtime to save context window.
• Sub-agent delegation: Register named sub-agents or use clone to delegate tasks to a worker agent with an isolated context.
• Planning: Optional PlanMode injects a write_todos tool that lets the agent maintain a step-by-step task list during execution.
• Context compression: LLMBasedContextCompressor summarizes old messages into episodic memory when the token count exceeds a threshold. The agent can recall original messages via the built-in retrieve_memory tool.
• Loop detection: DefaultLoopDetector catches repeated identical tool calls and can run periodic LLM-based diagnosis for subtler loops.
• Controller hooks: AgentController provides request/response interception points around every major step (before run, before LLM call, before/after each tool call), allowing the host application to approve or stop execution.
• System callback: A systemCallback function runs before every LLM call, letting you dynamically modify the system message, tools, or request messages.

Installation #

dependencies:
  dart_agent_core: ^1.0.3

Quick Start #

import 'dart:io';
import 'package:dart_agent_core/dart_agent_core.dart';

String getWeather(String location) {
  if (location.toLowerCase().contains('tokyo')) return 'Sunny, 25°C';
  return 'Weather data not available for this location';
}

void main() async {
  final apiKey = Platform.environment['OPENAI_API_KEY'] ?? '';
  final client = OpenAIClient(apiKey: apiKey);
  final modelConfig = ModelConfig(model: 'gpt-4o-mini');

  final weatherTool = Tool(
    name: 'get_weather',
    description: 'Get the current weather for a city.',
    executable: getWeather,
    parameters: {
      'type': 'object',
      'properties': {
        'location': {'type': 'string', 'description': 'City name, e.g. Tokyo'},
      },
      'required': ['location'],
    },
  );

  final agent = StatefulAgent(
    name: 'weather_agent',
    client: client,
    tools: [weatherTool],
    modelConfig: modelConfig,
    state: AgentState.empty(),
    systemPrompts: ['You are a helpful assistant.'],
  );

  final responses = await agent.run([
    UserMessage.text('What is the weather like in Tokyo right now?'),
  ]);

  print((responses.last as ModelMessage).textOutput);
}

Supported Providers #

OpenAI (Chat Completions) #

final client = OpenAIClient(
  apiKey: Platform.environment['OPENAI_API_KEY'] ?? '',
  // baseUrl defaults to 'https://api.openai.com'
  // Override for Azure OpenAI or compatible proxies
);

OpenAI (Responses API) #

Uses the newer stateful Responses API. The client automatically extracts responseId from ModelMessage and passes it as previous_response_id on subsequent requests, so only new messages are sent.

final client = ResponsesClient(
  apiKey: Platform.environment['OPENAI_API_KEY'] ?? '',
);

Google Gemini #

final client = GeminiClient(
  apiKey: Platform.environment['GEMINI_API_KEY'] ?? '',
);

AWS Bedrock (Claude) #

Uses AWS Signature V4 for authentication instead of a simple API key.

final client = BedrockClaudeClient(
  region: 'us-east-1',
  accessKeyId: Platform.environment['AWS_ACCESS_KEY_ID'] ?? '',
  secretAccessKey: Platform.environment['AWS_SECRET_ACCESS_KEY'] ?? '',
);

All clients support HTTP proxies via proxyUrl and configurable retry/timeout parameters. See Providers doc for details.

Tool Use #

Wrap any Dart function (sync or async) as a tool. The agent parses the LLM's function call JSON, maps arguments to your function's parameters, executes it, and feeds the result back.

final tool = Tool(
  name: 'search_products',
  description: 'Search the product catalog.',
  executable: searchProducts,
  parameters: {
    'type': 'object',
    'properties': {
      'query': {'type': 'string'},
      'maxResults': {'type': 'integer'},
    },
    'required': ['query'],
  },
  namedParameters: ['maxResults'], // maps to Dart named parameters
);

Tools can access the current session state via AgentCallToolContext.current without explicit parameters:

String checkBalance(String currency) {
  final userId = AgentCallToolContext.current?.state.metadata['user_id'];
  return fetchBalance(userId, currency);
}

Return AgentToolResult for advanced control:

Future<AgentToolResult> generateChart(String query) async {
  final imageBytes = await chartService.render(query);
  return AgentToolResult(
    content: ImagePart(base64Encode(imageBytes), 'image/png'),
    stopFlag: true,  // stop the agent loop after this tool
    metadata: {'chart_type': 'bar'},
  );
}

See Tools & Planning doc for positional/named parameter mapping, async tools, and more.

Skill System #

Skills are modular capability units — a system prompt plus optional tools bundled under a name. The agent can activate/deactivate skills at runtime to keep the context window focused.

class CodeReviewSkill extends Skill {
  CodeReviewSkill() : super(
    name: 'code_review',
    description: 'Review code for bugs and style issues.',
    systemPrompt: 'You are an expert code reviewer. Check for security issues and logic errors.',
    tools: [readFileTool, lintTool],
  );
}

final agent = StatefulAgent(
  ...
  skills: [CodeReviewSkill(), DataAnalysisSkill()],
);

• Dynamic skills (default): Start inactive. The agent gains activate_skills / deactivate_skills tools to toggle them based on the current task.
• Always-on skills (forceActivate: true): Permanently active, cannot be deactivated.

Sub-Agent Delegation #

Register sub-agents for specialized or parallelizable work. Each worker runs in its own isolated AgentState.

final agent = StatefulAgent(
  ...
  subAgents: [
    SubAgent(
      name: 'researcher',
      description: 'Searches the web and summarizes findings.',
      agentFactory: (parent) => StatefulAgent(
        name: 'researcher',
        client: parent.client,
        modelConfig: parent.modelConfig,
        state: AgentState.empty(),
        tools: [webSearchTool],
        isSubAgent: true,
      ),
    ),
  ],
);

The agent uses the built-in delegate_task tool to dispatch work:

• assignee: 'clone' — creates a copy of the current agent with clean context.
• assignee: 'researcher' — uses a registered named sub-agent.

Streaming #

runStream() yields fine-grained events for Flutter UI integration:

await for (final event in agent.runStream([UserMessage.text('Hello')])) {
  switch (event.eventType) {
    case StreamingEventType.modelChunkMessage:
      final chunk = event.data as ModelMessage;
      // update text in UI incrementally
      break;
    case StreamingEventType.fullModelMessage:
      // complete assembled message for this turn
      break;
    case StreamingEventType.functionCallRequest:
      // model requested tool calls
      break;
    case StreamingEventType.functionCallResult:
      // tool execution finished
      break;
    default:
      break;
  }
}

Planning #

Pass planMode: PlanMode.auto (or PlanMode.must) to enable the planner. This injects a write_todos tool that the agent uses to create and update a task list with statuses: pending, in_progress, completed, cancelled.

final agent = StatefulAgent(
  ...
  planMode: PlanMode.auto,
);

React to plan changes via AgentController:

controller.on<PlanChangedEvent>((event) {
  for (final step in event.plan.steps) {
    print('[${step.status.name}] ${step.description}');
  }
});

Context Compression #

For long-running sessions, attach a compressor to automatically summarize old messages when token usage exceeds a threshold:

final agent = StatefulAgent(
  ...
  compressor: LLMBasedContextCompressor(
    client: client,
    modelConfig: ModelConfig(model: 'gpt-4o-mini'),
    totalTokenThreshold: 64000,
    keepRecentMessageSize: 10,
  ),
);

Compressed history is stored as episodic memories. The agent can retrieve the original messages via the built-in retrieve_memory tool when the summary isn't detailed enough.

Controller Hooks #

AgentController provides lifecycle interception points:

final controller = AgentController();

// Pub/Sub: observe events
controller.on<AfterToolCallEvent>((event) {
  print('Tool ${event.result.name} finished');
});

// Request/Response: approve or block steps
controller.registerHandler<BeforeToolCallRequest, BeforeToolCallResponse>(
  (request) async {
    if (request.functionCall.name == 'delete_files') {
      return BeforeToolCallResponse(approve: false);
    }
    return BeforeToolCallResponse(approve: true);
  },
);

final agent = StatefulAgent(..., controller: controller);

System Callback #

For dynamic per-call modifications, use systemCallback — it runs before every LLM call and can modify the system message, tools, and request messages:

final agent = StatefulAgent(
  ...
  systemCallback: (agent, systemMessage, tools, messages) async {
    final updated = SystemMessage(
      '${systemMessage?.content ?? ''}\nCurrent time: ${DateTime.now()}',
    );
    return (updated, tools, messages);
  },
);

Examples #

See the example/ directory:

• Basic agent with tool use
• Streaming responses
• Persistent state across sessions
• Planning with write_todos
• Dynamic skill system
• Sub-agent delegation
• Controller hooks (observe & block)
• Claude extended thinking via Bedrock
• Gemini
• OpenAI

Documentation #

• Architecture & Lifecycle — Agent loop, streaming events, controller hooks, loop detection, cancellation
• LLM Providers & Configuration — OpenAI, Gemini, Bedrock setup, ModelConfig, proxy support
• Tools & Planning — Tool creation, parameter mapping, AgentToolResult, skills, sub-agents, planner
• State & Memory Management — AgentState, FileStateStorage, context compression, episodic memory

Contributing #

Bug reports and pull requests are welcome. Please open an issue first for significant changes.