Add audience role validation for MCP::Annotations per MCP specification#422
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koic merged 1 commit intoJun 21, 2026
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…cation The MCP specification constrains `Annotations.audience` to an array of `Role` values (`"user"` or `"assistant"`), but the Ruby SDK accepts any value. The other official SDKs already enforce this (TypeScript, Python, and PHP). This follows the existing pattern in `MCP::Icon`, which validates its constrained `theme` value in the constructor and raises `ArgumentError`. Added tests in `test/mcp/annotations_test.rb`: - valid `audience` (`["user"]`, `["assistant"]`, `["user", "assistant"]`, and an empty array) is accepted - an unknown role, a mixed valid/invalid array, or a non-array `audience` raises `ArgumentError` Existing tests used `["developers"]`, which is not a valid `Role`, and are updated to `["user"]`. The full unit suite and RuboCop pass locally. Strictly speaking this is a breaking change: a caller that currently passes an invalid `audience` (e.g. `["developers"]`) will now get an `ArgumentError`. Such values already violate the MCP specification, and `nil` / valid-role values are unaffected.
koic
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Jun 21, 2026
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Motivation and Context
The MCP specification constrains
Annotations.audienceto an array ofRolevalues ("user"or"assistant"), but the Ruby SDK accepts any value. The other official SDKs already enforce this — TypeScript, Python, and PHP.This follows the existing pattern in
MCP::Icon, which validates its constrainedthemevalue in the constructor and raisesArgumentError.How Has This Been Tested?
Added tests in
test/mcp/annotations_test.rb:audience(["user"],["assistant"],["user", "assistant"],and an empty array) is accepted
audienceraises
ArgumentErrorExisting tests used
["developers"], which is not a validRole, and areupdated to
["user"].The full unit suite and RuboCop pass locally.
Breaking Changes
Strictly speaking yes: a caller that currently passes an invalid
audience(e.g.
["developers"]) will now get anArgumentError. Such values alreadyviolate the MCP specification, and
nil/ valid-role values are unaffected.Types of changes
Checklist