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CLI write-note (and other tool subcommands) crash with 'function' object has no attribute 'fn' — no resolvable fastmcp version satisfies the 0.16.2 CLI bridge #944
Description
Version: basic-memory 0.16.2 (pip), Python 3.13
What happens
A fresh pip install basic-memory resolves fastmcp 3.4.2. Any basic-memory tool ... subcommand then fails:
$ echo "hello" | basic-memory tool write-note --title t --folder f
Error during write_note: 'function' object has no attribute 'fn'
The CLI bridge (basic_memory/cli/commands/tool.py) calls mcp_write_note.fn(...) — a fastmcp 2.x API. Under fastmcp 3.x the tool objects have no .fn.
Downgrading does not help: fastmcp==2.14.7 (newest 2.x) breaks a different import (ImportError: cannot import name 'PrivateKeyJWTClientAuthenticator' from 'fastmcp.server.auth.auth'). There is no fastmcp version that satisfies the 0.16.2 CLI, yet pyproject declares an open-ended fastmcp>=2.10.2.
Impact
The MCP-server path is unaffected (the tool functions work when called directly), so this is specifically the CLI bridge — but every documented basic-memory tool ... command is broken on a clean install.
Suggested fix
Pin a compatible fastmcp range in pyproject.toml, and/or update the CLI bridge to call the tool callables the way fastmcp 3.x exposes them (the underlying async functions are importable from basic_memory.mcp.tools).
Packaging note
fastmcp 3.4.2 ships its module via the fastmcp-slim package; a surgical uninstall/reinstall of fastmcp alone can leave an empty namespace package (fastmcp.__file__ is None). Worth a note in install docs.
— Reported by ArdurAI, from independent benchmarking of open-source agent-memory tools.
Activity
groksrc commentedon Jun 10, 2026
Thanks for the precise diagnosis — the mechanics are exactly right for 0.16.2. That release is from the fastmcp 2.x era: its open-ended
fastmcp>=2.10.2constraint predates fastmcp 3, so it installs alongside a 3.x it can't use, and its CLI bridge calls the 2.x-only.fn(...)API. This is already fixed in newer releases: 0.17.0 pinned fastmcp exactly, 0.19.0 migrated the CLI bridge to fastmcp 3, and the current release (0.21.6) pinsfastmcp==3.3.1with no.fncalls anywhere. The published 0.16.2 metadata on PyPI can't be amended retroactively.The fact that a fresh install resolved to 0.16.2 is the tell: pip backtracks to whatever old version's looser constraints fit the packages already in the environment — your fastmcp-slim note suggests a previously-mutated env, which is the classic trigger. In a clean venv,
pip install basic-memory(orpip install -U basic-memory) gets you 0.21.6 with a correctly pinned fastmcp, and thetoolsubcommands work on Python 3.13.Closing as fixed-in-current — please reopen if you can reproduce the crash on 0.21.6 in a clean environment.