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gemini-cli - ✅(Solved) Fix Developer Knowledge MCP returns "Method not supported" error in Gemini CLI (worked before Apr 8) [1 pull requests, 4 comments, 4 participants]

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google-gemini/gemini-cli#25107•Fetched 2026-04-11 06:31:35
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Error Message

However, since then, the MCP server started returning the following error: Error: Error discovering prompts from google-developer-knowledge: MCP error -32601: Method not supported 4. Observe error

PR fix notes

PR #25381: chore(mcp): check MCP error code over brittle string match

Description (problem / solution / changelog)

Summary

This PR enhances the stability of MCP server discovery by using specific MCP error codes instead of brittle string matching.

Previously

MCP server failure on prompt discovery for "Method not supported" showed a brittle match on "Method not found" so "Method not supported" was not being picked up.

<img width="1200" height="524" alt="Screenshot 2026-04-14 at 10 17 54 AM" src="https://github.com/user-attachments/assets/762d43d9-4ead-4986-854e-ef8349994321" />

Now

MCP prompts use proper error code to check discovery and return empty on error so tools can properly work.

<img width="1300" height="536" alt="Screenshot 2026-04-14 at 10 17 37 AM" src="https://github.com/user-attachments/assets/9b04d448-0fe8-4165-aa3d-be269ea8e506" />

Details

  • Replaced string-based error checking for "Method not found" with explicit McpError and ErrorCode.MethodNotFound checks.

Related Issues

Fixes #25107

Pre-Merge Checklist

  • Updated relevant documentation and README (if needed)
  • Added/updated tests (if needed)
  • Noted breaking changes (if any)
  • Validated on required platforms/methods:
    • MacOS
      • npm run
      • npx
      • Docker
      • Podman
      • Seatbelt

Changed files

  • packages/core/src/tools/mcp-client.test.ts (modified, +22/-0)
  • packages/core/src/tools/mcp-client.ts (modified, +9/-7)

Code Example

> /about
CLI Version: 0.37.1
Model: gemini-3-flash-preview
Sandbox: no sandbox
OS: darwin
Tier: Gemini Code Assist for individuals
RAW_BUFFERClick to expand / collapse

What happened?

I have been using the Developer Knowledge API MCP server with Gemini CLI without any issues until around April 8 (JST).

However, since then, the MCP server started returning the following error:

MCP issues detected. Run /mcp list for status.

/mcp list 🟢 google-developer-knowledge - Ready Error: Error discovering prompts from google-developer-knowledge: MCP error -32601: Method not supported

This issue occurs consistently and prevents the MCP from being usable.

What did you expect to happen?

The MCP server should work as before and allow prompt discovery without errors.

Client information

  • Gemini CLI versions tested:

    • 0.36.0
    • 0.37.0
    • 0.37.1

  • Platform:

    • macOS Tahoe 26.3.1 (a)

  • MCP:

    • google-developer-knowledge
<details> <summary>Client Information</summary> 
> /about
CLI Version: 0.37.1
Model: gemini-3-flash-preview
Sandbox: no sandbox
OS: darwin
Tier: Gemini Code Assist for individuals
</details>

Login information

I tested both authentication methods and the issue occurs in both cases:

  • oauth-personal
  • vertex-ai

Therefore, this does not seem to be related to a specific authentication method.

Anything else we need to know?

  • The Developer Knowledge API is enabled in Google Cloud.
  • An API key is created and restricted to only the Developer Knowledge API.
  • The Developer Knowledge MCP server is enabled in the project.

Additionally, this issue does NOT occur in other tools:

  • Claude Code → works fine
  • Cursor → works fine

This suggests the issue may be specific to Gemini CLI.

Reference: https://developers.google.com/knowledge/mcp

Steps to reproduce:

  1. Enable Developer Knowledge API in Google Cloud
  2. Configure MCP server (google-developer-knowledge)
  3. Run /mcp list
  4. Observe error

extent analysis

TL;DR

The issue with the MCP server returning an error may be resolved by checking the compatibility of the Gemini CLI version with the Developer Knowledge API MCP server.

Guidance

  • Verify that the Gemini CLI version is compatible with the Developer Knowledge API MCP server by checking the official documentation or release notes.
  • Check the MCP server configuration to ensure it is correctly set up and enabled for the google-developer-knowledge API.
  • Test the MCP server with a different CLI version or tool to isolate the issue and determine if it's specific to the Gemini CLI.
  • Review the API key restrictions to ensure they are correctly configured for the Developer Knowledge API.

Example

No code snippet is provided as the issue does not require a code change, but rather a configuration or compatibility check.

Notes

The issue may be specific to the Gemini CLI, as other tools like Claude Code and Cursor work fine. However, without further information, it's difficult to determine the root cause.

Recommendation

Apply workaround: Check the compatibility of the Gemini CLI version with the Developer Knowledge API MCP server and test with a different version or tool if necessary. This is recommended because the issue may be related to a specific version or configuration of the Gemini CLI.

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gemini-cli - ✅(Solved) Fix Developer Knowledge MCP returns "Method not supported" error in Gemini CLI (worked before Apr 8) [1 pull requests, 4 comments, 4 participants]