What
MCP servers are add-ons that give Claude extra tools. Their tools can return structured content, meaning data laid out in fixed fields, alongside the usual text. If that structured content is over a size limit, Claude Code now leaves it off the result message. It sets structuredContentOmitted on the tool result so the gap is recorded.
Two cases are exempt:
- tools that declare a UI panel through
_meta.ui - in-process SDK servers, meaning MCP servers running inside the same program as Claude Code
Why
Very large tool results no longer fill up the conversation. Claude does not see the structured part of those results, though, so an MCP tool that returns a lot of structured data will reach Claude without it.
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The exact size limit is not known.