Basic Agent Usage

The following shows simple agent usage using the Agent() constructor, which takes a model string.

void main() async {
  // Create an agent with a model string and a system prompt
  final agent = Agent(
    'openai',  // Can also use 'openai:gpt-4o' or 'openai/gpt-4o'
    systemPrompt: 'Be concise, reply with one sentence.',
  );

  // Run the agent with a prompt (non-streaming)
  final result = await agent.run('Where does "hello world" come from?');
  print(result.output); // Output: one sentence on the origin of "hello world"
}

Alternatively, you can use the Agent() constructor which takes a provider directly:

void main() async {
  // Create an agent with a provider
  final agent = Agent.provider(
    OpenAiProvider(),
    systemPrompt: 'Be concise, reply with one sentence.',
  );

  // Run the agent with a prompt (non-streaming)
  final result = await agent.run('Where does "hello world" come from?');
  print(result.output); // Output: one sentence on the origin of "hello world"
}

Model Strings

The model string used by Agent can be specified in several ways:

• Just the provider, e.g. openai → specifies whatever the default model for that provider
• provider:model, e.g. google:2.0-flash → specifies a provider and model, seperated by a colon
• provider/model, e.g. googleai/gemini-2.5-pro → specifies a provider and model, seperated by a slash

Providers

A provider is a Dart type like GeminiProvider that knows how to expose model objects (like GeminiModel). When you pass in a model string, you're really looking up a provider object and a model object for the agent to do its work.

You can see the list of Supported Providers that Dartantic exposes. And you can see build your own Custom Providers if you like.

Provider Aliases

Some providers support multiple provider prefixes. The alias can be used where the provider name is specified, e.g. gemini:gemini-2.0-flash → google:gemini-2.0-flash. Here's where you can see the list of aliases for each of the Supported Providers.