What’s the Difference Between an MCP Server and MCP Client?

TL;DR:

• The MCP Client is the agent’s access layer — it requests credentials and presents tokens.

• The MCP Server is the platform’s control layer — it issues tokens, enforces delegation rules, and logs activity.

If you think in OAuth terms:

• Client = the agent (like a bot, LLM, or automation)

• Server = the SaaS platform it’s trying to access.

🧠 Why This Matters

As you implement Machine Client Protocol (MCP) in your app or platform, you'll need to decide:

• Who’s hosting the server?

• Who’s building the client integration?

• Where do delegation, token issuance, and auditing happen?

Let’s break down each side.

🤖 What Is an MCP Client?

An MCP Client is the agent-side component. It’s the logic that lives inside the agent (or is bundled with it) that:

• Requests credentials (either directly or via delegated setup)

• Handles token acquisition from an MCP server

• Presents tokens when calling downstream APIs

• Refreshes or revokes tokens as needed

Think of it as the identity and access interface for the agent.

Common Examples:

• A GPT plugin needing access to a user’s CRM

• A customer-side automation tool acting on behalf of a user

• An LLM orchestrator calling a third-party SaaS API

The client might be:

• A library

• A lightweight SDK

• A runtime wrapper around the agent

🔐 What Is an MCP Server?

An MCP Server is the provider-side infrastructure. It’s the component your platform exposes to:

• Receive client identity requests

• Verify agent identity and delegation

• Issue scoped, signed access tokens

• Log all access attempts and actions

• Provide auditability and revocation

Think of the MCP server as the access gatekeeper for your platform’s APIs — it decides:

• Who gets in

• What they can do

• How long they can do it

• Whether it’s safe to allow it

🛠️ How MCP Server and Client Work Together

1. Client Requests Access

The agent’s MCP client requests a token for access, often including:

• Agent ID

• Requested scopes

• Delegation proof (if acting on behalf of a user or org)

2. Server Verifies and Issues Token

The MCP server:

• Authenticates the agent

• Validates the delegation chain

• Issues a signed, scoped token

3. Client Calls API

The agent uses that token to access your API, with:

• TTL (time-to-live)

• Scope restrictions

• Tracing metadata

4. Server Logs Everything

The MCP server logs:

• Who accessed what

• When, and for how long

• Whether access was revoked or refreshed

• Audit metadata

📊 Quick Comparison Table

🧱 Analogy: Driver vs. Toll Booth

• MCP Client = the driver (agent) who wants to access the highway (API)

• MCP Server = the toll booth that checks identity, validates the ticket, and logs every crossing

🚀 How Prefactor Helps

At Prefactor, we provide a drop-in MCP server — so you don’t have to build it from scratch.

You focus on:

• Enabling secure agent access

• Defining scopes and permissions

• Delivering your core product

We handle:

• Token issuance

• Delegation validation

• Audit trail

• Revocation logic

And your customers can use our MCP client SDKs or build their own — securely.

✅ Summary

• MCP Clients are for agents who need access

• MCP Servers are for platforms granting access

• Both are essential parts of a secure, scalable agent access flow

If your app is being accessed by bots, LLMs, or customer-side automations — you’ll need both sides of MCP.

Sign up for a chat with the Founders today to find out more.