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 Model Context 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- Whether access was revoked or refreshed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.