Every LLM app built before 2025 invented its own tool schema. Then Anthropic shipped MCP, Claude adopted it, OpenAI adopted it, and by 2026 it is the default wire format for connecting any LLM to any tool, data source, or agent. Write one MCP server and every host talks to it.
You ship a chatbot that needs three tools: a database query, a calendar API, and a file reader. You write three JSON schemas for Claude. Then sales wants the same tools in ChatGPT — you rewrite them for OpenAI's tools parameter. Then you add Cursor, Zed, and Claude Code — three more rewrites, each with subtly different JSON conventions. A week later, Anthropic adds a new field; you update six schemas.
This was the pre-2025 reality. Every host (the thing running an LLM) and every server (the thing exposing tools and data) shipped bespoke protocols. Scaling meant an N×M integration matrix.
Model Context Protocol collapses that matrix. One JSON-RPC-based spec. One server exposes tools, resources, and prompts. Any compliant host — Claude Desktop, ChatGPT, Cursor, Claude Code, Zed, and a long tail of agent frameworks — can discover and call them without custom glue.
As of early 2026, MCP is the default tool-and-context protocol across the big three (Anthropic, OpenAI, Google) and every major agent harness.
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