Remove special-casing of string enumerables in McpServerTool #699
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We special-case string enumerables, translating them to an array of text content blocks, but other enumerables just get serialized, and there's a reasonable expectation that returning a string[] would produce a JSON array of strings. Just delete the special-casing.
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Yeah, agree. One downside is that it's no longer possible to return multiple text blocks by using string array as the return type. And it's a valid signature for tools (can make sense in some cases, as it's different schema wise at the LLM api level). I can't recall if it's possible to return this via array of text AIContent. If so, nothing lost. |
You can return an AIContent[], a TextContentBlock[], or even a CallToolResult. |
AArnott
approved these changes
Aug 12, 2025
eiriktsarpalis
approved these changes
Aug 12, 2025
PederHP
approved these changes
Aug 13, 2025
halter73
approved these changes
Aug 13, 2025
stephentoub
merged commit 70960e1
into
modelcontextprotocol:main
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We special-case string enumerables, translating them to an array of text content blocks, but other enumerables just get serialized, and there's a reasonable expectation that returning a string[] would produce a JSON array of strings. Just delete the special-casing.
Fixes #698
cc: @AArnott