[4ktLuffy]

Description

When an MCP tool call returns a result with isError=true, the span currently looks like a success, so failed tool calls can't be counted or alerted on. This sets error.type to "tool_error" on the span in that case, for both the mcp 1.x handler wrapper and the mcp 2.x tool-call middleware (including the 2.x MCPServer, which turns a raised tool exception into an isError result).

This follows the OTel MCP conventions, which say error.type SHOULD be "tool_error" when a CallToolResult has isError set to true:
https://github.com/open-telemetry/semantic-conventions-genai/blob/4a39b6ef1363fab57bc40e18c82abb32cc89ebcd/docs/gen-ai/mcp.md#L187-L192
It also matches what the JS SDK does.

The span status is left unchanged, as discussed in the issue (the JSON-RPC call itself succeeded, like the GraphQL 200 case). No custom attribute is added.

Tests cover isError true/false, a raising MCPServer tool, and a raised exception in a lowlevel handler (no error.type, existing behaviour), in static and streaming mode, on mcp 2.x and 1.x.

Issues

• resolves: MCP integration records tool calls that return isError as successful #7890

[alexander-alderman-webb]

Closing as this needs further discussion per the issue.