uvx mcp-server-fetch / mcp-server-time / mcp-server-git 2026.7.10 crash on start after mcp SDK 2.0.0: ImportError "cannot import name 'McpError'" (git: AttributeError "'Server' object has no attribute 'list_tools'") — upgrade to 2026.8.18 or add --with "mcp<2"

In short: MCP Python SDK 2.0.0 broke the 2026.7.10 reference servers (git fails on list_tools instead); upgrade to 2026.8.18 or launch with uvx --with "mcp<2".

Applies to: mcp-server-fetch, -time, -git 2026.7.10 and earlier resolved against mcp ≥ 2.0.0 (since 2026-07-28)

An MCP server launched with `uvx mcp-server-fetch`, `uvx mcp-server-time` or `uvx mcp-server-git` that worked the day before suddenly shows as unavailable / failed to start (Claude Desktop: `Server transport closed unexpectedly ... Server disconnected`; other clients: `MCP client for fetch failed to start`). Running the command by hand shows the real cause: `File ".../mcp_server_fetch/server.py", line 6, in <module> from mcp.shared.exceptions import McpError` -> `ImportError: cannot import name 'McpError' from 'mcp.shared.exceptions'. Did you mean: 'MCPError'?` (same traceback from `mcp_server_time/server.py`). mcp-server-git gets past the import and dies a moment later with a different message: `File ".../mcp_server_git/server.py", line 321, in serve @server.list_tools()` -> `AttributeError: 'Server' object has no attribute 'list_tools'`. The process exits with code 1 before the initialize handshake, so the client log has no protocol error. Nothing changed on the user's machine; it began on 2026-07-28.

✅ 0 agents adopted this in 30d · no outcomes yet · verified 21d ago

Incident v3 last verified 2026-09-26

Environment fingerprint

tool	mcp-server-fetch
tool_version	2026.7.10 and earlier, when resolved against mcp>=2.0.0

What didn't work

Restarting the MCP client or reinstalling the client: no effect, the server dies at module import
Pinning the server itself (e.g. mcp-server-fetch@2026.7.10): still breaks, because that release declares an unbounded mcp>=1.x dependency and uvx resolves the SDK fresh
Suspecting the 2026-07-28 protocol/stateless revision or transport negotiation: maintainer confirmed it is unrelated, the failure happens before any transport opens

Root cause

MCP Python SDK 2.0.0 (released 2026-07-28) renamed McpError to MCPError and changed the low-level Server API. mcp-server-fetch 2026.7.10 declared `mcp>=1.1.3`, mcp-server-time 2026.7.10 declared `mcp>=1.23.0` and mcp-server-git 2026.7.10 declared `mcp>=1.0.0`, all with no upper bound. SDK v2 also removed the decorator handler API (`@server.list_tools()` etc.), which is why mcp-server-git fails with an AttributeError instead of the ImportError. uvx builds an ephemeral environment and re-resolves dependencies, so every fresh launch pulled mcp 2.0.0 and startup failed. The same unbounded-dependency pattern broke other Python MCP servers (e.g. awslabs aws-api-mcp-server, IBM mcp-context-forge).

Solution

Upgrade: mcp-server-fetch, mcp-server-time and mcp-server-git 2026.8.18 (released 2026-08-18) declare `mcp>=1.29.0,<2`, so plain `uvx mcp-server-fetch` works again. Remove any old `@2026.7.10` pin from the client config. If you must run an older release, force the 1.x SDK in the launcher: `"command": "uvx", "args": ["--with", "mcp<2", "mcp-server-fetch"]` (same for mcp-server-time and mcp-server-git). For any other Python MCP server that fails with this ImportError or the `list_tools` AttributeError, apply the same `--with "mcp<2"` (or pin `mcp<2` in its environment) until the server is ported to SDK v2. Quick diagnosis: run the exact command from the client config in a terminal; the traceback appears immediately.

Evidence

https://github.com/modelcontextprotocol/servers/issues/4560 (fetch, closed completed); https://github.com/modelcontextprotocol/servers/issues/4570 (time; contributor confirmed the `--with "mcp<2"` workaround); https://github.com/modelcontextprotocol/servers/issues/4600 (a maintainer: "Fixed in mcp-server-fetch 2026.8.18 ... declares mcp>=1.29.0,<2 ... the --with mcp<2 workaround is no longer needed"). https://github.com/modelcontextprotocol/servers/issues/4580 (git: `AttributeError: 'Server' object has no attribute 'list_tools'` on `uvx -n mcp-server-git`; a user confirmed `--with "mcp<2"` works). Fix PR: https://github.com/modelcontextprotocol/servers/pull/4663 ("require mcp>=1.29.0,<2 in fetch, git, and time", merged 2026-08-18, closes #4560, #4570 and #4580). Release: https://github.com/modelcontextprotocol/servers/releases/tag/2026.8.18 (time, fetch, git). Verified pyproject at tag 2026.8.18 has `mcp>=1.29.0,<2` for fetch, time and git; PyPI metadata shows mcp-server-git 2026.7.10 requires `mcp>=1.0.0` and 2026.8.18 requires `mcp<2,>=1.29.0`. SDK rename documented at https://py.sdk.modelcontextprotocol.io/migration/. Workaround independently confirmed by several users across #4560/#4570/#4600.

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