Locus product guide · Updated November 10, 2026

What is MCP? The Model Context Protocol explained

MCP (Model Context Protocol) is an open standard that lets an AI application use outside tools and data through one interface. A host such as Claude Code or VS Code runs one MCP client per server. Each server offers tools, resources and prompts as JSON-RPC 2.0 messages over stdio or Streamable HTTP. The current spec version, 2026-07-28, makes every request stateless.

What problem does MCP solve?

Before MCP, each AI app needed its own integration for each tool. MCP replaces that with one protocol. A developer builds a server once, and any MCP host can use it. The MCP docs compare it to a USB-C port for AI applications.

Claude, ChatGPT, Visual Studio Code and Cursor all support MCP. Anthropic open-sourced the protocol, which David Soria Parra and Justin Spahr-Summers created. The first spec revision is dated 2024-11-05. The project now runs as Model Context Protocol a Series of LF Projects, LLC.

How does MCP work?

MCP has three roles. The host is the AI application, such as Claude Code. The host creates one MCP client for each server it connects to. The server is the program that provides tools and data.

A local server runs on your machine as a child process and talks over stdio. It usually serves one client. A remote server runs on the internet and talks over Streamable HTTP. It usually serves many clients.

Every message is JSON-RPC 2.0. Since 2026-07-28, each request carries its protocol version and client capabilities in a _meta field. There is no handshake and no session. A client can call server/discover first to learn what a server supports, or just send a request.

What can an MCP server offer?

Servers expose three primitives. Each has a different owner who decides when it is used. Clients can also offer elicitation, which lets a server ask the user for input.

What can an MCP server offer?
Primitive	Who controls it	What it is	Example
Tools	The model	Functions the model calls to act or fetch data	Run a web search, create a ticket
Resources	The application	Data the client attaches as context	File contents, a database schema
Prompts	The user	Templates the user picks	A slash command or menu option
Elicitation	The user answers it	A server request for more input, offered by the client	Ask for a username before a lookup

What changed in each MCP version?

MCP versions are dates. A new date marks a change that breaks compatibility. The 2026-07-28 revision is current. Clients and servers can support several versions and fall back to older ones.

What changed in each MCP version?
Version	Main changes
2024-11-05	First published revision. Remote servers used the HTTP+SSE transport.
2025-03-26	Streamable HTTP replaced HTTP+SSE. An authorization section was added.
2025-06-18	Elicitation added. HTTP clients send an MCP-Protocol-Version header.
2025-11-25	Experimental tasks for long-running work.
2026-07-28 (current)	Stateless requests, server/discover, no sessions. Client ID Metadata Documents replace dynamic client registration as the preferred sign-up. Roots, sampling and logging are deprecated.

How do MCP transports and sign-in work?

MCP defines two standard transports. Stdio sends newline-delimited messages to a process the client launched. Streamable HTTP sends each message as an HTTP POST to one endpoint, and the server replies with JSON or a short SSE stream.

Authorization is optional in MCP. An HTTP server that needs it uses OAuth 2.1. The server publishes protected resource metadata, and the client signs in through the browser and sends a bearer token on every request. A stdio server reads its credentials from the environment instead.

MCP does not replace APIs. It is a way for an agent to find and call them. For when to call an API or SDK directly, see MCP vs API vs SDK.

What does it cost to call paid tools over MCP?

The protocol is free. The services behind a server may charge. Most paid APIs want their own account and API key before your agent can call them.

Locus Pro puts many paid APIs behind one hosted MCP server at https://api.paywithlocus.com/api/credits/mcp. You sign in once with OAuth. Search, describe and balance checks are free. Each paid call is charged its catalog price from one prepaid credit balance, and 1,000 credits equal $1. Prices checked November 10, 2026.

What does it cost to call paid tools over MCP?
Tool on Locus Pro	Price per call	In US dollars
Firecrawl search	1.7 credits, fixed	About $0.0017
Perplexity search	Up to 5.8 credits	Up to about $0.0058
Hunter email finder	1 to 10.1 credits	$0.001 to $0.0101
Brave web search	30.3 credits, fixed	About $0.0303

When should I use MCP?

Use MCP when an agent should pick tools at run time inside an MCP host. Use something else when the job is different.

Your own code knows exactly which call to make: call the API or SDK directly.
The agent needs instructions for a task, not a new tool: write a skill.
The agent must act in a user’s own Gmail or Slack: use an OAuth connector platform such as Composio.
The agent needs paid data APIs it has no account for: use Locus Pro over MCP.
One API at steady, high volume: call that provider with your own account and API key, which can cost less per call.

Frequently asked questions

Who created MCP?

Anthropic open-sourced MCP. David Soria Parra and Justin Spahr-Summers created it. The project is now run as an LF Projects series with its own maintainers, and anyone can propose changes.

What is the latest MCP version?

The current version is 2026-07-28. It removed the initialize handshake and sessions, so every request stands alone. Servers must answer server/discover with their versions and capabilities.

Do I need to code to use an MCP server?

No. Most hosts take a server URL or a launch command in settings. You then sign in if the server asks. Building your own server does take code, and official SDKs exist for several languages.

Is MCP only for Claude?

No. It is an open standard. ChatGPT, VS Code, Cursor and many other clients support it, so one server works across all of them.

Implementation references

Use these first-party references for current request contracts and account requirements. Tool availability, prices, and negotiated terms can change.

Sources

Third-party details were checked on November 10, 2026. Vendors change pricing and features often, so confirm on their site before you decide.