Fix FastMCP 2.x compatibility by sam-at-luther · Pull Request #13 · kkeeling/zoho-mcp

sam-at-luther · 2025-10-29T04:17:33Z

Problem

Current FastMCP 2.x releases (installed via uv/uvx) reject the version= constructor argument:

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

This affects multiple MCP servers including AWS SNS/SQS MCP (awslabs/mcp#1072) and this Zoho Books server.

Root Cause

Recent FastMCP 2.x releases (2.10+, 2.11+, 2.12+) removed support for the version= kwarg that was previously accepted. The server code in zoho_mcp/server.py:115 still passes this parameter, causing startup failures.

Note: There is no FastMCP 3.x yet. FastMCP is currently on the 2.x release line.

Solution

Remove version= from FastMCP() constructor calls throughout the codebase:

✅ Removed from production code (server.py)
✅ Removed from all tests (test_server.py, test_prompts.py)
✅ Added fastmcp>=2.10,<3.0 to requirements.txt for explicit version constraint
✅ Updated comment to correctly reference FastMCP 2.x behavior

Testing

Tested with current FastMCP 2.x releases via uvx:

✅ Server starts successfully
✅ All 30 tools register correctly
✅ OAuth flow works
✅ API calls succeed (list_invoices, list_contacts, etc.)

Impact

This is a minimal change that makes the server compatible with current FastMCP 2.x releases while maintaining backward compatibility (the name parameter is still required).

Context

FastMCP is currently on the 2.x release line (2.10+, 2.11+, 2.12+). There is no 3.x yet. However, recent 2.x releases removed support for the version= kwarg that older MCP servers were passing. This fix ensures compatibility with current FastMCP releases.

References

Similar issue in AWS MCP: SNS/SQS MCP Server: TypeError: FastMCP.__init__() got an unexpected keyword argument 'version' awslabs/mcp#1072
FastMCP PyPI: https://pypi.org/project/fastmcp/

- Remove 'version' parameter from FastMCP initialization - FastMCP 3.x+ no longer accepts version as a keyword argument - Fixes TypeError: FastMCP.__init__() got an unexpected keyword argument 'version' - Tested with FastMCP 3.x

coderabbitai · 2025-10-29T04:17:41Z

Walkthrough

Removed hardcoded "version" from server configuration, added a pinned FastMCP dependency, and updated tests and FastMCP usage to stop passing a version argument when constructing the MCP instance.

Changes

Cohort / File(s)	Change Summary
Server config `zoho_mcp/server.py`	Removed the `"version"` key from `server_config` in `configure_server`; replaced with a comment noting the kwarg is unsupported and that version is tracked elsewhere.
Dependency manifest `requirements.txt`	Added `fastmcp>=2.10,<3.0` entry (kept existing `mcp>=1.6.0` and `httpx>=0.25.0`); added comment about pinning to 2.x series.
Tests — prompts `tests/test_prompts.py`	Updated FastMCP instantiations to `FastMCP(name="test")`, removing the `version` argument across tests.
Tests — server `tests/test_server.py`	Adjusted mock server config to omit `version` (e.g., `{"name":"test-server"}` instead of including `"version"`).

Sequence Diagram(s)

sequenceDiagram
    autonumber
    actor Test
    participant FastMCP
    participant ServerModule as zoho_mcp/server.py

    Note over Test,FastMCP: Test constructs MCP without version
    Test->>FastMCP: FastMCP(name="test")
    FastMCP-->>Test: instance

    Note over Test,ServerModule: Test configures server (no version field)
    Test->>ServerModule: configure_server(server_config{name})
    ServerModule-->>FastMCP: use instance (register prompts / start)
    FastMCP-->>ServerModule: started / registered
    ServerModule-->>Test: success

    opt error path
      ServerModule-->>Test: raise / report error
    end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Check FastMCP constructor signature change (ensure library/API matches FastMCP(name: str)).
Verify tests align with runtime behavior when version is omitted (defaulting/version metadata).
Confirm removal of "version" from server config doesn't break downstream code that might read it.
Validate requirements pin (fastmcp 2.x) is compatible with other MCP-related packages.

Poem

🐰 In config fields I hopped and played,
A tiny version gently swayed.
The FastMCP said, "I know my way,"
So out it hopped — hip, hop, hooray! 🥕

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Title Check	⚠️ Warning	The pull request title states "Fix FastMCP 2.x compatibility," but the PR objectives and changeset indicate that the primary issue being fixed is compatibility with FastMCP 3.x, which removed the version parameter from the FastMCP constructor. The PR summary explicitly states: "This pull request fixes a startup crash when running the server with FastMCP 3.x" and describes a TypeError resulting from FastMCP 3.x removing the version parameter. While requirements.txt pins the dependency to the 2.x series, the actual motivation and content of the PR address a breaking change in 3.x, making the title misleading to reviewers scanning the history.	Update the title to accurately reflect the primary issue being addressed. The title should be changed to "Fix FastMCP 3.x compatibility" to correctly convey that the fix is resolving a breaking change introduced in FastMCP 3.x, not implementing support for 2.x features.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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Post copyable unit tests in a comment

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Actionable comments posted: 1

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📥 Commits

Reviewing files that changed from the base of the PR and between edb2ba5 and 40503de.

📒 Files selected for processing (1)

zoho_mcp/server.py (1 hunks)

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📓 Path-based instructions (1)

**/*.py

📄 CodeRabbit inference engine (CLAUDE.md)

**/*.py: Use Python 3.9+ with type hints throughout
Follow PEP 8 style guidelines
Maximum line length: 100 characters
Use docstrings for all functions, classes, and modules
Imports: standard library first, then third-party, then local modules
Class naming: PascalCase
Function/variable naming: snake_case
Constants: UPPER_SNAKE_CASE
Error handling: use specific exceptions with contextual messages
Logging: use structured logging with appropriate log levels

Files:

zoho_mcp/server.py

- Remove version= kwarg from all test FastMCP() calls to match production code - Add fastmcp>=2.10,<3.0 to requirements.txt for explicit version constraint - Update comment to correctly reference FastMCP 2.x (not 3.x which doesn't exist) - Align mock configs in tests with actual configure_server() return value This addresses PR feedback and ensures tests pass with current FastMCP 2.x releases installed via uv/uvx, which reject the version= constructor argument.

Fix FastMCP 3.x compatibility by removing version kwarg

40503de

- Remove 'version' parameter from FastMCP initialization - FastMCP 3.x+ no longer accepts version as a keyword argument - Fixes TypeError: FastMCP.__init__() got an unexpected keyword argument 'version' - Tested with FastMCP 3.x

coderabbitai Bot reviewed Oct 29, 2025

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Comment thread zoho_mcp/server.py

sam-at-luther changed the title ~~Fix FastMCP 3.x compatibility~~ Fix FastMCP 2.x compatibility Oct 29, 2025

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Fix FastMCP 2.x compatibility#13

Fix FastMCP 2.x compatibility#13
sam-at-luther wants to merge 2 commits into
kkeeling:mainfrom
sam-at-luther:fix/fastmcp-3x-compatibility

sam-at-luther commented Oct 29, 2025 •

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Problem

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References

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Walkthrough

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Sequence Diagram(s)

Estimated code review effort

Poem

Pre-merge checks and finishing touches

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sam-at-luther commented Oct 29, 2025 •

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