URL: https://gofastmcp.com/more/faq
Title: FAQ - FastMCP

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import fastmcp stopped working after I upgraded with pip
What’s the difference between fastmcp and fastmcp-slim?
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Answers to common questions about installing and using FastMCP
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​
import fastmcp
stopped working after I upgraded with pip
This can happen when you upgrade to FastMCP 3.3 or later from FastMCP 3.2 or earlier with
pip
. The quick fix is
pip install --force-reinstall fastmcp
. See
Troubleshooting
for the clean-reinstall fallback and an explanation of why it happens.
​
What’s the difference between
fastmcp
and
fastmcp-slim
?
fastmcp
is the full distribution. Installing it gives you the complete framework — server, client, CLI, and the common integrations — and is the right choice for most users:
pip
install
fastmcp
fastmcp-slim
ships the same importable
fastmcp
package with a minimal set of required dependencies. You opt into the pieces you need through extras, which keeps environments lean when you only use part of the framework:
pip
install
"
fastmcp-slim[client]
"
Both distributions expose the same
import fastmcp
, so application code is identical regardless of which one you install.
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