Unclear Which MCP connections use the mcp-wire-codec format, and so skip the result check, is not stated.
What
Claude Code connects to outside tools through MCP, the Model Context Protocol. It has changed how it checks the replies those tools send back:
- Replies from one particular message format, called
mcp-wire-codec, now skip the step that checked each result against its expected structure. Before, every complete result was checked. - The check for each tool's output is now prepared only when that tool needs it, rather than for every tool at once. It is prepared for all tools when a structure definition contains
"$id". - Incoming messages are now checked by simpler built-in structure checks.
Why
Listing tools can now cost less work. It could also change which badly formed replies are accepted from an MCP server.
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Which MCP connections use the `mcp-wire-codec` format, and so skip the result check, is not stated.