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Sweep 27 Oct 2026 · 19:04Z Build v2.1.312 531 read Stable v2.1.308 Latest v2.1.312 Next v2.1.312 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.311 ·

MCP servers can send structured results in an encoded form

Claude Code can now decode MCP structured results sent under the claude/structuredContentJsonBase64 key and show them as JSON text

You'll notice Improvements
JSON All of v2.1.311
You'll noticeTier: how much it should matter to you
3Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
MCPArea: what it touches
ImprovementsKind: in v2.1.311,
ImprovementsSection of the release

Unclear The switch that controls the decoding was not identified, so it is unclear whether it is active for you.

What

MCP servers are outside programs that give Claude Code extra tools. A tool can return structured content, which is data in a fixed shape. Claude Code now handles a new form of it:

  • when a result's structured content holds only the key claude/structuredContentJsonBase64, Claude Code decodes it into JSON text, behind a switch
  • image results from an MCP tool can now be passed through a separate image-reading step
  • reading a folder from an MCP server can now be cancelled partway

Claude Code also reports an error when it tries to read a folder from a server that does not offer folder reading.

Why

MCP servers get another way to send structured results, which Claude can then read as plain JSON text.

How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtThe switch that controls the decoding was not identified, so it is unclear whether it is active for you.

See this entry in the whole of v2.1.311 →

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