An MCP server connects an MCP-compatible application to a system’s data and capabilities through a common interface. It can offer callable tools, contextual resources, and reusable prompts; its handlers still do the application-specific work of reaching an API, database, file system, or other service. Developers need one when that interface provides useful MCP compatibility or integration reuse—not simply because an application uses AI.
What an MCP server does
An MCP server implements the server side of the Model Context Protocol. An application—often called the host, and using an MCP client to connect—can discover capabilities exposed by the server and mediate how they are used with a model. The server is an interface to an underlying system, not the system or the model itself. The official TypeScript SDK documentation describes this client-server relationship and the SDK’s serving options.
The protocol standardizes how capabilities are presented and requested. It does not supply the underlying business logic: a registered server handler must connect to the relevant API, database, files, or other system and return or act on the result.
What an MCP server can expose
| Capability | What it provides | Typical use |
|---|---|---|
| Tools | Discoverable functions that a client can invoke with arguments. | Querying an API, calculating a value, or changing a file. |
| Resources | Contextual data exposed through URI-based access or resource templates. | Providing reference material or other data to an application. |
| Prompts | Named, reusable templates or instructions that a host may present or invoke. | Offering a consistent starting point for a task. |
These categories are distinct: tools perform operations, resources provide data, and prompts package reusable instructions. The MCP server overview explains the primitives and their control roles.
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Tools: operations the client can request
A server registers tools and their handlers. A client can list the available tools and call one by name with arguments; the server runs the handler. The model may help select a tool, but it is the server—not the model—that executes the registered operation. See the official TypeScript SDK client guide for the list-and-call flow.
Resources: data for context
Resources make data available to the host or application as context. They are not inherently actions for a model to execute. Depending on the server, they can be addressed directly or made available through resource templates.
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Prompts: reusable templates
Prompts let a server offer named templates or instructions. How a host presents or uses them depends on that host’s implementation; server instructions are not guaranteed to be handled the same way everywhere. The official guidance on server instructions recommends evaluating the target client’s behavior rather than assuming it will follow a particular pattern.
How the client and server work together
- The host application connects to an MCP server through an MCP client.
- The client discovers the server’s available capabilities, such as tools, resources, or prompts.
- The host mediates how those capabilities are used with the model or presented to the user.
- When an operation is requested, the server’s registered handler carries it out against the underlying system and returns a result.
For example, an order-system server could expose a lookup-order tool and a resource containing permitted order documentation. A compatible assistant could request an order lookup and present the returned information. This illustrates the documented tool and resource patterns; it is not a claim about a particular deployment.
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When developers need an MCP server
An MCP server is a good fit when a system must be available to MCP-compatible applications and its functions or data can be represented as discoverable tools, resources, or prompts. It is especially useful when multiple compatible clients may reuse the same integration: the server provides a common interface rather than requiring each host to build a separate, host-specific connection.
- The target application supports MCP and needs access to the system.
- The integration has useful operations, contextual data, or reusable prompts to expose.
- Supporting more than one compatible host makes an interoperable interface worthwhile.
- The team can define which actions are allowed, validate inputs, and control access to data and operations.
These are practical architecture criteria, not formal protocol requirements. If one fixed application is the only intended consumer and a direct API call already meets the need, an MCP server may add an unnecessary layer. It is also not a solution when the target application does not support MCP.
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MCP server or direct integration?
Choose based on the application’s requirements, not on a blanket assumption that every AI integration should use MCP.
| Question | MCP server is a stronger fit when… | Direct integration may be simpler when… |
|---|---|---|
| Who must connect? | The system needs to work with MCP-compatible clients. | Only one fixed application needs the connection, and it does not need MCP compatibility. |
| Will the integration be reused? | Multiple hosts could benefit from the same discoverable interface. | The connection is specific to one application and reuse is not valuable. |
| What should be exposed? | Capabilities map cleanly to tools, resources, or prompts. | A straightforward application call already supplies what the single consumer needs. |
| Who owns safety and operations? | The team can manage permissions, validation, and server operation for exposed capabilities. | Adding a separately operated interface would not solve a real need. |
| Will versions work together? | The server SDK and target clients support a compatible protocol revision. | The extra protocol and SDK compatibility work outweighs interoperability benefits. |
What changed in the 2026-07-28 specification
The official specification release announcement identifies 2026-07-28 as the current specification revision as of this article’s publication date, 2026-10-04. It describes breaking changes: the former initialize/initialized exchange and Mcp-Session-Id header were removed, request metadata travels with each request, and clients can optionally use server/discover to obtain capabilities up front. Older implementations may follow earlier revisions, so check their supported version rather than assuming they use the new behavior.
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For remote HTTP deployments, the release also describes distributing requests across instances without protocol-level sticky sessions or a shared session store, operation-routing headers, list/read cache hints, and updated authorization requirements. The official roadmap dated 2026-08-22 summarizes the operational direction: a remote MCP server can be run like another HTTP workload. These details are revision-sensitive; verify compatibility with the chosen SDK and target client.
The TypeScript SDK v2 documentation identifies v2 as its stable line implementing the 2026-07-28 specification and documents stdio and HTTP serving options. These are TypeScript SDK details; other languages may differ in package names, supported transports, and migration steps.
Security responsibilities and practical limits
A tool can affect a connected system, so exposing it is a security decision—not just a way to make an API discoverable. Limit tools to intended actions, validate their inputs, and apply authorization appropriate to the data and effects involved. Protocol support, including the authorization changes described in the 2026 release, does not establish that an individual server deployment is safe.
Also test the host’s actual behavior. In particular, do not rely on a server prompt or instruction being used exactly as intended without evaluating the target host with the server and its tools.
Quick Recap
A decision checklist before building
- Confirm that the intended host or hosts support MCP.
- Map each desired capability to a tool, resource, or prompt; avoid exposing actions the client does not need.
- Decide who will implement and operate the handlers that connect to the underlying system.
- Set authorization, input validation, and boundaries for any tool that can change data or trigger an operation.
- Check the specification revision and SDK support on both sides, particularly when connecting an older implementation to the 2026-07-28 revision.
- Test discovery, invocation, host behavior, and failure handling with the actual client.
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