fix: remove structuredContent from MCP tool results#13
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MaxwellCalkin wants to merge 1 commit intoagentmail-to:mainfrom
Open
fix: remove structuredContent from MCP tool results#13MaxwellCalkin wants to merge 1 commit intoagentmail-to:mainfrom
MaxwellCalkin wants to merge 1 commit intoagentmail-to:mainfrom
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structuredContent requires tools to declare an outputSchema (per the MCP
spec), which these tools don't. When the raw API result is a string
instead of a record, the MCP SDK raises:
MCP error -32602: Invalid tools/call result:
expected record, received string
Removing structuredContent fixes Claude Code and other spec-compliant
MCP clients. The content field already returns the full result as
JSON text, so no information is lost.
Fixes agentmail-to/agentmail-mcp#5
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
structuredContentfield from MCP tool callback results innode/src/mcp.tsMCP error -32602Root Cause
The
structuredContentfield in the MCP spec requires tools to declare anoutputSchema. Since these tools don't declare one, the SDK validatesstructuredContentagainst no schema and fails. Additionally, when the API result is a string (e.g. fromdeleteInbox), validation fails with "expected record, received string".The
contentfield already returns the full result as pretty-printed JSON text, so no information is lost.Test plan
agentmail-toolkitinagentmail-mcpclaude mcp listto verify server connectslist_inboxesfrom Claude Code — should return results without-32602errordelete_inbox(string result) — should also work🤖 Generated with Claude Code
Summary by cubic
Removed structuredContent from MCP tool results to comply with the spec when no outputSchema is declared. Fixes MCP error -32602 in Claude Code and other spec-compliant clients while preserving full output via the content field as pretty-printed JSON (agentmail-to/agentmail-mcp#5).
Written for commit c29f407. Summary will update on new commits.