Defining Agents

Agents are defined using the Arc Agent DSL.

Example

agent {
    name = "weather"
    description = "Agent that provides weather data."
    model { "gemma:7b" }
    prompt { """
       You are a professional weather service.
       You have access to real-time weather data with the get_weather function.
       Keep your answer short and concise.
       All you require is the location.
       if you cannot help the user, simply reply "I cant help you"
     """
    }
    tools {
        +"get_weather"
    }
}

Overview

Name	Description
name	The name of the Agent. This should be a unique identifier. Preferably without special characters.
model	The model that should be provided to the Agent.
description	A short description of what the Agent does.
prompt	The System Prompt of the Agent. The prompt defines the core objective, goals and instructions for Agents.
tools	A list of tools/functions that the Agent uses, see.
filterInput	Defines filter logic, see.
filterOutput	Defines filter logic, see.
limit	Defines a rate limiter, see.
onFail	Called when the Agent encounters an Exception, see.

See the following pages on how to load the agents into your application.

• Manual Setup
• Spring Boot Beans

Prompt templating

The prompt function of an Agent is called on each request. Meaning that it can be dynamically customized to best suit the current context. Now although Kotlin Strings are quite powerful, adding logical constructs such as if and for loops statements can be cumbersome.

For this purpose, the Arc DSL overwrites the UnaryPlus operator, +, within the prompt block to allow for simple string concatenation.

For example, the following code snippet shows how to use the + operator to build a dynamic prompt.

agent {
    prompt {
        +"Here is the first part og the prompt."
        if(someCondition) {
            +"Here is a conditional part of the prompt."
        }
      "The last part of the prompt (this does not require a + because it is automatically returned)."
    }
}

OnFail

The onFail property allows you to define custom error handling behavior for your agent. When an agent encounters an exception during execution, the code defined in the onFail block will be executed.

This is particularly useful for:

• Providing fallback responses when the agent fails
• Implementing retry mechanisms
• Gracefully handling expected exceptions

Example:

agent {
    name = "weather"
    onFail { 
        if (condition) {
            retry(reason = "Condition is not fulfilled.")
        } else if (anotherCondition) {
            AssistantMessage("New message!")
        } else null
    }
    prompt {
        val retry = getOptional<RetrySignal>()
        if (retry != null) {
            // The details provided to the retry function can be accessed here.
            """ Updated Instructions with ${retry.reason}"""
        } else {
            """ Instructions """
        }
    }
}

The onFail block receives the exception that was thrown as a parameter, allowing you to inspect the error and respond accordingly.

The onFail block can either:

• return an AssistantMessage which will be returned to the client as if the agent executed successfully.
• return null in which case the agent will rethrow the exception.
• call the retry function which will cause the agent to be re-run.

For more details on the retry function, see Retry.