# MCP vs everything: API, RAG, A2A, Claude Skills, function calling

MCP gets compared to five things it mostly isn't competing with. One page per pairing — the direct answer first, then a table, then when to use which.

- [MCP vs API](https://mcpyet.com/compare/mcp-vs-api.md) — a layer on top, not a replacement. APIs expose a product to developers; MCP re-exposes it to AI models.
- [MCP vs RAG](https://mcpyet.com/compare/mcp-vs-rag.md) — a protocol vs a technique, complementary. RAG grounds a model in documents; MCP wires it to live systems.
- [MCP vs A2A](https://mcpyet.com/compare/mcp-vs-a2a.md) — tools vs teammates. MCP connects one agent to its tools; A2A connects agents to each other.
- [MCP vs Claude Skills](https://mcpyet.com/compare/mcp-vs-claude-skills.md) — know-how vs connections. A Skill teaches a procedure; an MCP server gives live access.
- [MCP vs function calling](https://mcpyet.com/compare/mcp-vs-function-calling.md) — MCP standardizes what function calling started.

## The short version

The [Model Context Protocol](https://mcpyet.com/what-is-mcp.md) is plumbing: a standard way for AI assistants to discover and call external capabilities. APIs are what it plumbs into. RAG is a retrieval technique it can carry. A2A operates one layer up, between whole agents. Skills package instructions rather than connections. And function calling is the model-side mechanism MCP builds on. If a comparison page tells you one of these "kills" another, it's selling something.

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Source: https://mcpyet.com/compare/ — data refreshed 2026-08-11