TypeError: FastMCP.__init__() got an unexpected keyword argument 'dependencies' when starting awslabs.core-mcp-server

Question

Why does awslabs.core-mcp-server fail on macOS with "TypeError: FastMCP.__init__() got an unexpected keyword argument 'dependencies'" when added to Cursor?

AgentArmorHQ team · Accepted Answer

Unfixed: the issue was closed as stale without a resolution in the thread. The only workaround reported is to pin `awslabs.core-mcp-server@0.2.5`.

The crash happens because `server.py` line 69 in the 1.x releases passes `dependencies=[...]` to `FastMCP(...)`. Recent FastMCP versions (2.13.3 and 2.14.1 are mentioned in the thread) no longer accept that argument. Since the package does not pin a compatible FastMCP version, `uv` installs the latest FastMCP and the server fails immediately with:

```
TypeError: FastMCP.__init__() got an unexpected keyword argument 'dependencies'
```

Every 1.x version from 1.0.0 through 1.0.15 reproduces the same error.

Workaround: configure your MCP client (Cursor, Kiro, etc.) to launch the server with:

```bash
uvx awslabs.core-mcp-server@0.2.5
```

A commenter confirmed that the server starts healthy with this version. Note that 0.2.5 and earlier releases do not have the role-based dynamic proxy server loading introduced in 1.x, so this is not a full replacement if you depend on that feature.

AgentArmorHQ team · Answer

**What @whrocha tried on GitHub** (Worked)

Pinned the server to awslabs.core-mcp-server@0.2.5; the server then worked, though this version lacks the 1.x dynamic proxy feature.

Source: https://github.com/awslabs/mcp/issues/1951#issuecomment-3666724806

AgentArmorHQ team · Answer

**What @TheTechOddBug tried on GitHub** (Didn't work)

Ran `uvx awslabs.core-mcp-server@1.0.15` and verified every version from 1.0.0 to 1.0.15 fails identically with the same TypeError.

Source: https://github.com/awslabs/mcp/issues/1951#issuecomment-3671788635

AgentArmorHQ team · Answer

**What a GitHub user tried on GitHub** (Didn't work)

Reporter tried uv with Python ^3.11 and then 3.14.2, and cleared the uv cache; the same TypeError appeared every time.

Source: https://github.com/awslabs/mcp/issues/1951

TypeError: FastMCP.init() got an unexpected keyword argument 'dependencies' when starting awslabs.core-mcp-server

4 answers