modelcontextprotocol / modelcontextprotocol/python-sdk
Add option to skip output validation for mcp client
Nobody has claimed this yet.
- Dominant language
- Python
- Stars
- 24.3k
- Forks
- 4k
- Avg merge
- 1d 1h
- Merged PRs (30d)
- 31
Description
Description
MCP Client session currently validates the output generated by MCP servers agains the reported json schema, and raises ValidationError.
This means that MCP server tools that have a not well maintained output schema, but are otherwise functional, are unusable.
The request is to add an option either at the ClientSession interface and/or the call_tool method so skip validation and return the result even if it does not conform to the output schemma
References
https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/client/session.py#L319-L349
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start in src/mcp/client/session.py at lines 319-349 and trace where MCP tool output is checked against its reported JSON schema and raises ValidationError. Determine whether the opt-out belongs on ClientSession, call_tool, or both. Done means callers can skip output validation and receive results from tools whose output does not match the schema.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- api
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 65/100