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Revive low-level SDK upgrade guide for SDK v2 era

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Jeremiah Lowin 2026-07-06 16:50:58 -04:00
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10
docs/getting-started/upgrading/from-low-level-sdk.mdx
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@ -9,16 +9,18 @@ If you've been building MCP servers directly on the `mcp` package's `Server` cla
The core idea: instead of telling the SDK what your tools look like and then separately implementing them, you write ordinary Python functions and let FastMCP derive the protocol layer from your code. Type hints become JSON Schema. Docstrings become descriptions. Return values are serialized automatically. The plumbing you wrote to satisfy the protocol just disappears.
<Note>
This guide covers upgrading from **v1** of the `mcp` package. We'll provide a separate guide when v2 ships.
</Note>
## Why now is the moment to switch
MCP SDK v2 landed sweeping breaking changes on the low-level `Server`: the protocol types moved out of `mcp.types` into a separate `mcp_types` package, every field was renamed from camelCase to snake_case, the `Server` class was rebuilt, `McpError` was renamed, and sessions were removed on the new sessionless protocol era. If you build directly on the low-level SDK, all of that lands on you — you have to rewrite your imports, your handler signatures, and your error construction to match the new surface.
Adopting FastMCP is the easier path. FastMCP 4 runs on SDK v2 and hides that entire surface behind a high-level API that did not change. You write `@mcp.tool` and never touch the renamed internals — FastMCP derives the protocol layer from your function signatures, so the SDK v2 rename simply isn't something your code has to know about. Migrating low-level-SDK-v1 code to FastMCP is less work than migrating it to raw SDK v2, and you come out the other side with the whole framework: composition, middleware, proxies, authentication, and testing. The SDK v2 break is the natural moment to make the jump.
<Note>
Already using FastMCP 1.0 via `from mcp.server.fastmcp import FastMCP`? Your upgrade is simpler — see the [FastMCP 1.0 upgrade guide](/getting-started/upgrading/from-mcp-sdk) instead.
</Note>
<Prompt description="Copy this prompt into any LLM along with your server code to get automated upgrade guidance.">
You are upgrading an MCP server from the `mcp` package's low-level Server class (v1) to FastMCP 3.0. The server currently uses `mcp.server.Server` (or `mcp.server.lowlevel.server.Server`) with manual handler registration. Analyze the provided code and rewrite it using FastMCP's high-level API. The full guide is at https://gofastmcp.com/getting-started/upgrading/from-low-level-sdk and the complete FastMCP documentation is at https://gofastmcp.com — fetch these for complete context.
You are upgrading an MCP server from the `mcp` package's low-level Server class (v1) to FastMCP 4. The server currently uses `mcp.server.Server` (or `mcp.server.lowlevel.server.Server`) with manual handler registration. Analyze the provided code and rewrite it using FastMCP's high-level API. The full guide is at https://gofastmcp.com/getting-started/upgrading/from-low-level-sdk and the complete FastMCP documentation is at https://gofastmcp.com — fetch these for complete context.
UPGRADE RULES:

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docs/getting-started/upgrading/from-mcp-sdk.mdx
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@ -32,7 +32,7 @@ uv add fastmcp
FastMCP includes the `mcp` package as a dependency, so you don't lose access to anything. Update your import, run your server, and if your tools work, you're done.
<Prompt description="Copy this prompt into any LLM along with your server code to get automated upgrade guidance.">
You are upgrading an MCP server from FastMCP 1.0 (bundled in the `mcp` package v1) to standalone FastMCP 3.0. Analyze the provided code and identify every change needed. The full upgrade guide is at https://gofastmcp.com/getting-started/upgrading/from-mcp-sdk and the complete FastMCP documentation is at https://gofastmcp.com — fetch these for complete context.
You are upgrading an MCP server from FastMCP 1.0 (bundled in the `mcp` package v1) to standalone FastMCP 4. Analyze the provided code and identify every change needed. The full upgrade guide is at https://gofastmcp.com/getting-started/upgrading/from-mcp-sdk and the complete FastMCP documentation is at https://gofastmcp.com — fetch these for complete context.
STEP 1 — IMPORT (required for all servers):
Change "from mcp.server.fastmcp import FastMCP" to "from fastmcp import FastMCP".