AI Agents vs AI Systems for Software Architecture
Bruna Gomes | Aug 20, 2025
With the rise of LLMs, the possibilities of artificial intelligence have expanded dramatically, from summarizing texts and answering complex questions to generating code, creating images, and supporting decision-making.
Behind many of these capabilities lies the concept of AI agents: systems that use LLMs as the “brain” to interact with the world, perform tasks, and autonomously achieve goals.
But this is only the beginning. By introducing protocols like MCP (Model Context Protocol) and A2A (Agent-to-Agent Protocol), the potential grows even further.
These protocols enable agents not only to connect with external tools and real-time data but also to collaborate, combining their different specializations to solve more complex problems.
Before diving into the protocols, it’s worth taking a moment to understand what AI agents are and how they work in practice.
Then, we’ll explore how to make them even more powerful through MCP and A2A, unlocking new possibilities for interaction and collaboration.
AI agents are autonomous software systems that perceive their environment, make decisions, and act to achieve human-defined goals.
Powered by LLMs, they can interpret inputs, generate plans, and decide on actions in a continuous loop rather than waiting for explicit step-by-step instructions.
Typically, an agent combines three core elements:
Together, these elements turn agents from passive tools into proactive collaborators capable of handling complex workflows end to end.
A key characteristic of AI agents is their ability to decide and act autonomously. These actions can include querying databases, updating enterprise systems, running internal workflows, or calling external APIs.
In this setup, the LLM handles reasoning while integrations enable real-world execution. Without a standard, these integrations become complex to maintain, and that’s where the Model Context Protocol (MCP) helps, by providing a unified way for agents to connect with tools and perform tasks reliably
AI agents are most effective when working within a specific context, like scheduling, CRM, or finance.
This specialization makes them efficient, but it also creates a limitation: to solve broader problems, agents need a way to collaborate across different domains, and that’s where protocols like A2A come into play.
Also read: AI Agents vs AI Systems for Software Architecture
The Model Context Protocol (MCP) is an open standard introduced by Anthropic to make AI agents more powerful and interoperable. Its purpose is to provide a structured way for agents to connect with tools, services, and real-time data, enabling them to move beyond passive reasoning into actionable execution.
Instead of being tied to one-off integrations, MCP creates a common interface that allows any MCP-compliant agent to use external resources such as APIs, calendars, databases, or enterprise systems in a consistent way.
The problem MCP addresses is the integration bottleneck. Without it, every agent must be hard-coded to interact with each external service it needs, including custom authentication, API schemas, and error handling.
As the number of agents and tools grows, this quickly turns into an M×N problem: each agent must integrate with each service separately, making the system fragile and costly to maintain. MCP simplifies this by standardizing discovery and interaction, so that once a tool is described in MCP, any compliant agent can use it immediately.
Internally, MCP organizes the interaction between an AI agent and external tools into three main components:
In most implementations, the Host (user-facing app) and Client (connector logic) reside together within the same application.
The Server, however, can be either an external API or implemented within the same application, depending on where the tools or services are hosted.
The communication between these components happens through well-defined payloads:
Imagine a user asking their AI assistant: “Plan a business trip to New York next week.”
Without MCP, the agent would need custom-coded integrations for every external service involved, such as flights, hotels, calendar, email, and more. Each integration would be unique, fragile, and difficult to maintain.
With MCP, however, the process becomes seamless. The assistant can:
The Host (chat interface) passes the request to the Client, which then orchestrates tool calls defined in MCP. Each tool is described with a clear schema, so the agent knows exactly what inputs are required and what outputs to expect.
In the end, the user receives a complete itinerary with flights booked, hotel reserved, and meetings scheduled, all within a single reasoning loop powered by MCP.
The Agent-to-Agent Protocol (A2A) is an open standard introduced by Google in 2025. It allows AI agents to discover, communicate, and collaborate with each other across different platforms.
While MCP focuses on connecting agents to tools and data, A2A provides the rules for agents themselves to exchange tasks and coordinate their efforts.
The main problem A2A solves is the lack of interoperability between agents. Without a standard, each new agent must implement custom discovery, authentication, and message formats to interact with others.
This quickly becomes fragile and inefficient. A2A removes this barrier by defining a consistent protocol for discovery and communication, enabling specialized agents from different domains to collaborate seamlessly on complex tasks.
Internally, A2A organizes the interaction between AI agents into a few key components:
The communication between agents happens through well-defined messages:
The communication flow typically begins when a client agent reads an Agent Card to discover another agent’s capabilities.
It then creates a task request and sends it as a message. The server agent updates the task status as it progresses, for example, from “in progress” to “waiting for input” and finally “completed.”
Once finished, the server returns the result as an artifact, which may include text, structured data, or files. This lifecycle ensures transparency, coordination, and reliable collaboration between agents.
Imagine a company planning a product launch. A coordinator agent receives the request and needs help across multiple domains. Instead of calling every tool directly, it discovers specialized agents through their Agent Cards and delegates.
A2A lets domain experts remain focused while collaborating through a consistent protocol for discovery, task exchange, status updates, and artifacts.
The result is a modular, cross-domain workflow without bespoke, brittle integrations between every pair of agents.
MCP and A2A work best when combined. MCP gives agents a standardized way to access tools and real-time data, while A2A provides the rules for agents to discover each other and collaborate across domains.
Together, they enable AI agents not only to act in the world but also to coordinate with one another, creating scalable multi-agent ecosystems.
AI agents reach their full potential when they can both act in the world and collaborate across domains. MCP and A2A provide the standards that make this possible, paving the way for more scalable and interoperable agent ecosystems.
I am a software developer, graduated in Computer Science from the Federal University of Ceará in 2017. I enjoy working on improving performance in data processing queries, and my strongest experience lies in backend development. I am a curious professional who is always eager to learn new things. I have experience with cloud resources, but I am always looking to expand my knowledge in this area. I constantly strive to stay up-to-date with the latest trends and advancements in the technology market and to improve my skills in programming, teamwork, and problem-solving. I am always ready to take on new challenges and contribute to successful projects.