modelcontextprotocol / modelcontextprotocol/servers
Claude Code Sonnet 4.5 randomly crash with sequentialthinking (MCP)
Open
Nobody has claimed this yet.
bug
server-sequentialthinking
- Dominant language
- TypeScript
- Stars
- 90.5k
- Forks
- 11.7k
- Avg merge
- 2d 2h
- Merged PRs (30d)
- 5
Description
Describe the bug
When an Agent tries to use MCP, it crashes randomly sometimes.
To Reproduce
Steps to reproduce the behavior:
- Claude Code Sonnet 4.5
- Trigger sequentialthinking (MCP)
Expected behavior
It should be working the same as sonnet 4
Logs
sequential-thinking - sequentialthinking (MCP)(thought: XXX)
Error: {
"error": "Invalid thoughtNumber: must be a number",
"status": "failed"
}
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 with the sequentialthinking MCP tool and trace the validation that produces “Invalid thoughtNumber: must be a number.” Reproduce the failure with Claude Code Sonnet 4.5 and compare it with Sonnet 4, then verify that valid sequential-thinking requests no longer crash or reject the thought number.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100