MCP Server Pydantic validation error after recent merge

[jwheeler88]

Bug Description

The Serena MCP server fails to start with Pydantic validation errors after recent changes merged to main branch overnight.

Error Details

pydantic_core._pydantic_core.ValidationError: 14 validation errors for Settings
debug
  Field required [type=missing, input_value={...}, input_type=dict]
log_level
  Field required [type=missing, input_value={...}, input_type=dict]
mount_path
  Field required [type=missing, input_value={...}, input_type=dict]
sse_path
  Field required [type=missing, input_value={...}, input_type=dict]
message_path
  Field required [type=missing, input_value={...}, input_type=dict]
streamable_http_path
  Field required [type=missing, input_value={...}, input_type=dict]
json_response
  Field required [type=missing, input_value={...}, input_type=dict]
stateless_http
  Field required [type=missing, input_value={...}, input_type=dict]
warn_on_duplicate_resources
  Field required [type=missing, input_value={...}, input_type=dict]
warn_on_duplicate_tools
  Field required [type=missing, input_value={...}, input_type=dict]
warn_on_duplicate_prompts
  Field required [type=missing, input_value={...}, input_type=dict]
dependencies
  Field required [type=missing, input_value={...}, input_type=dict]
auth
  Field required [type=missing, input_value={...}, input_type=dict]
transport_security
  Field required [type=missing, input_value={...}, input_type=dict]

Environment

• Platform: Linux (WSL2)
• Installation: uvx --from git+https://github.com/oraios/serena
• Command: uvx --from git+https://github.com/oraios/serena serena start-mcp-server --context ide-assistant --project /path/to/project
• Version: 0.1.3-d8859286-dirty

Context

This was working yesterday but started failing after the recent merge to main branch. The MCP server starts up and loads the project successfully, but fails during Settings initialization, preventing proper MCP protocol communication.

Expected Behavior

MCP server should start without Pydantic validation errors and connect properly to Claude Code.

Actual Behavior

Server fails with 14 missing required fields in Settings class, suggesting default values were removed or the Settings class structure changed without updating the initialization code.

[patrickstump]

Yep, just hit me too.

From AI analysis:
Root cause identified: A recent commit (25c70988) to the Serena repository broke MCP compatibility by introducing Pydantic validation errors. The working version was commit b7c96b48.

The breakage happened between your working session earlier today (13:38) and when it failed (15:11) due to an upstream code change that introduced breaking MCP compatibility issues.

[visigoth]

i tried using @<tag> as a workaround, but it didn't work.

[jwheeler88]

@visigoth You'll need to reconfigure Claude Code to run from a local copy of the repo.

1. Clone the repo
2. cd /path/to/serena/repo
3. git checkout v1.3.0 to checkout latest stable release
4. claude mcp add serena [-s user] -- uv run --directory /abs/path/to/serena/repo serena-mcp-server --context ide-assistant

You should then be good to go until the team can get a fix in place.

[LukePeltier]

Appears to be related to this change

modelcontextprotocol/python-sdk#1198

Was able to fix by cloning serena and editing the pyproject.toml to specify mcp==1.12.2

[MischaPanch]

Fixed in 9cf5ee2, it was a breaking change in the official mcp SDK which they honored by raising the patch version from 1.12.2 to 1.12.3

I was also today years old when I found out that our committed uv.lock is ignored when using uvx on the directory...

@LukePeltier thanks for pinpointing the issue

[MischaPanch]

@patrickstump

From AI analysis: Root cause identified: A recent commit (25c70988) to the Serena repository broke MCP compatibility by introducing Pydantic validation errors. The working version was commit b7c96b48.

Just to clarify (and one more example of AI failing) - the cause has nothing to do with commits to serena but by a new patch release of the mcp sdk which broke backwards compatibility.

[Jannik2099]

could you tag a new release for this? the current pypi release is unusable thanks to this.

[MischaPanch]

@Jannik2099 done