> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vijil.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# What is an Agent

> An overview of AI agents and how to test them with Vijil.

<Tip>
  **TL;DR:** An AI agent is an autonomous system that can observe its environment, make decisions, and take actions, often using external tools. Vijil evaluates Agents using automated adversarial testing and assigns a [Trust Score](/concepts/trust-score/introduction) (0–100) measuring [reliability](/concepts/trust-score/reliability), [security](/concepts/trust-score/security), and [safety](/concepts/trust-score/safety).
</Tip>

An AI agent is an autonomous system powered by artificial intelligence designed to achieve specific goals. Unlike standard software that follows rigid rules, an Agent can observe its environment, make decisions, take actions and use external tools to complete tasks.

## Types of Agents

Agents come in different forms depending on their complexity and the tasks they handle:

<Card title="Single-Purpose Agents" icon="text-align-start" horizontal>
  Designed to do one specific task very well, such as answering customer support questions or scheduling meetings.
</Card>

<Card title="Orchestrator Agents" icon="text-align-start" horizontal>
  Orchestrator Agents act as managers. They break down complex problems and delegate tasks to other sub-agents.
</Card>

<Card title="Multimodal Agents" icon="text-align-start" horizontal>
  Agents that can process and generate different types of data, such as text, images, and audio.
</Card>

<Card title="Autonomous Agents" icon="text-align-start" horizontal>
  Highly independent Agents that can run continuously, adapt to new information, and learn over time without human intervention.
</Card>

## Approaches to Developing Agents

Building an Agent involves giving it the right tools and instructions:

1. **Prompt Engineering**: The simplest approach. You give a large language model (LLM) detailed instructions and examples of how to behave.
2. **Retrieval-Augmented Generation (RAG)**: The Agent searches external documents and data.
3. **Tool Use and APIs**: The Agent gets access to external tools (like calculators, web browsers, or your company's APIs) so it can perform actions in the real world.
4. **Agent Frameworks**: Developers often use frameworks like [LangChain](https://www.langchain.com/) or [AutoGen](https://microsoft.github.io/autogen/stable//index.html) to build complex systems where multiple agents work together.

## Approaches to Testing Agents

Testing agents is difficult because their outputs are not always predictable. Tools like [Vijil](https://vijil.ai/) provide a platform for you to [Evaluate](/concepts/evaluation-components/introduction) and [Defend](/concepts/defense/introduction) your agents.

Agents are commonly tested in these three ways:

| Approach                 | How It Works                                                                                                                               | Limitation                                                                                       |
| ------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------ |
| **Manual Testing**       | Humans interact with the agent to check behavior                                                                                           | Slow, does not scale, misses adversarial edge cases                                              |
| **Unit Testing**         | Tests individual components in isolation                                                                                                   | Misses failures that only emerge when the full system runs                                       |
| **Automated Evaluation** | Sends hundreds of adversarial [Probes](/concepts/evaluation-components/probe) across [Scenarios](/concepts/evaluation-components/scenario) | Requires agent registration and [Harness](/concepts/evaluation-components/harness) configuration |

Vijil measures your Agent's performance and assigns a [Trust Score](/concepts/trust-score/introduction). The Trust Score helps you understand if the Agent is safe, secure, and reliable enough for production.

## Managing Your Agents as an Owner

As an Agent Owner, your focus is on the business value and safety of the Agent. You need to ensure that the agent follows company policies and provides a good user experience.

Vijil gives you the tools to:

* **[Set Policies](/owner-guide/simulate-environment/policies)**: Define what the Agent is allowed and not allowed to do.
* **[Define Personas](/owner-guide/simulate-environment/personas).**: Test how the Agent reacts to different types of users.
* **[Run Evaluations](/owner-guide/run-evaluations/running-evaluations)**: How your AI agent against targeted scenarios to measure its trustworthiness.
* **[Protect Agents](/owner-guide/protect-in-production/configuring-guardrails)**: Set up runtime protection for your AI agents with Dome guardrails.