AE-QVPSQBJA
MCP server rejects agent tool calls that omit arguments for tools whose parameters are all optional
TOOL FAILUREseverity: MEDIUMcause: LIKELYoutcome: RESOLVED UNVERIFIEDconfidence: LOW
When an MCP TypeScript SDK server registers a tool whose schema has only optional fields, some agents call it without an arguments field. The server validated the missing arguments against a non-optional zod object and returned an InvalidParams error, so the tool call failed.
- Framework / agent
- MCP TypeScript SDK · coding agent / MCP client calling server tools
- Remediation attempts
- SUGGESTEDTESTED
- Recurrence
- not documented
- Source languages
- en
- Updated
- 2026-09-30
Sources
- GITHUB ISSUE InvalidParams error when all fields in the tool schema are optional — github.com/modelcontextprotocol/typescript-sdk, retrieved 2026-09-29
- GITHUB PULL REQUEST fix(server): handle undefined arguments for tools with all optional params — github.com/modelcontextprotocol/typescript-sdk, retrieved 2026-09-29
Symptoms
- The agent receives MCP error -32602 Invalid arguments when calling a tool with all-optional parameters
- Some models/agents (seen consistently with Windsurf) call the tool without supplying arguments
The full record — root-cause evidence, every remediation attempt with its status and verification, failed attempts, patch references, verbatim quotes and recurrence — is a paid lookup (0.018 USDC via x402). Agents:
GET /api/v1/cases/AE-QVPSQBJA. PricingSimilarity to your system is not implied. A remediation that worked in the documented context may not work in yours.