feat: Implement SEP-986: Tool Name Guidance

[vincent0426]

Implement SEP-986: Tool Name Guidance for Tool Type

Changes

• Added a length check that raises an error when the tool name is not within the allowed range:

  raise ValueError(f"Invalid tool name length: {len(value)}. Tool name must be between 1 and 128 characters.")

• Added a regex validation using re.compile(r"^[A-Za-z0-9_.-]+$") that raises an error for invalid characters:

  raise ValueError("Invalid tool name characters. Allowed: A-Z, a-z, 0-9, underscore (_), dash (-), dot (.).")

Motivation and Context

Related issues: SEP-986 #1537

Implements the guidance from modelcontextprotocol/modelcontextprotocol#986

- Tool names SHOULD be between 1 and 128 characters in length (inclusive).
- Tool names SHOULD be considered case-sensitive.
- The following SHOULD be the only allowed characters: uppercase and lowercase ASCII letters (A-Z, a-z), digits
  (0-9), underscore (\_), dash (-), and dot (.)
- Tool names SHOULD NOT contain spaces, commas, or other special characters.
- Tool names SHOULD be unique within a server.
- Example valid tool names:
  - getUser
  - DATA_EXPORT_v2
  - admin.tools.list

How Has This Been Tested?

Unit Tests

Valid Values

• getUser
• DATA_EXPORT_v2
• admin.tools.list
• a
• Z9_.-
• "x" * 128 (max length)

Invalid Values

• "" (empty string)
• "x" * 129 (exceeds max length)
• has space
• comma,name
• not/allowed
• name@
• name#
• name$

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[Kludex]

@maxisbey This is a less verbose way to write the same thing:

from typing import Annotated

from pydantic import StringConstraints

tool: Annotated[str, StringConstraints(max_length=128, pattern=r"^[A-Za-z0-9_.-]+$")]

---

I'm not sure if this should be applied on BaseMetadata, but if not, please drop the inheritance, and apply this here.

[Kludex]

Btw, most or all the field_validators in this code source can be replaced by proper annotated versions - that you can see are cuter.

[Kludex]

I personally don't think there's a need to test that Pydantic is working as expected.

[maxisbey]

We don't want it to actually fail, instead we'd want it to raise a deprecation warning