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Add support for _meta field on tool schema (#124)

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* Add support for _meta field on tool schema

* use `meta` naming for `_meta` field on tool schema

* apply suggestions to fix `_meta` tests

Co-authored-by: Ateş Göral <ates@magnetiq.com>

* Update lib/mcp/tool.rb

Co-authored-by: Ateş Göral <ates@magnetiq.com>

* Update lib/mcp/tool.rb

Co-authored-by: Ateş Göral <ates@magnetiq.com>

---------

Co-authored-by: Topher Bullock <topherbullock@users.noreply.github.com>
Co-authored-by: Ateş Göral <ates@magnetiq.com>
This commit is contained in:
Tyler Untisz 2025-10-01 15:21:27 -06:00 • committed by GitHub
commit 73cec83b99
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GPG key ID: B5690EEEBB952194
4 changed files with 71 additions and 3 deletions
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4
lib/mcp/server.rb
View file

@ -96,8 +96,8 @@ module MCP
end
end
def define_tool(name: nil, title: nil, description: nil, input_schema: nil, annotations: nil, &block)
tool = Tool.define(name:, title:, description:, input_schema:, annotations:, &block)
def define_tool(name: nil, title: nil, description: nil, input_schema: nil, annotations: nil, meta: nil, &block)
tool = Tool.define(name:, title:, description:, input_schema:, annotations:, meta:, &block)
@tools[tool.name_value] = tool
validate!

14
lib/mcp/tool.rb
View file

@ -8,6 +8,7 @@ module MCP
attr_reader :title_value
attr_reader :description_value
attr_reader :annotations_value
attr_reader :meta_value
def call(*args, server_context: nil)
raise NotImplementedError, "Subclasses must implement call"
@ -21,6 +22,7 @@ module MCP
inputSchema: input_schema_value.to_h,
outputSchema: @output_schema_value&.to_h,
annotations: annotations_value&.to_h,
_meta: meta_value,
}.compact
end
@ -32,6 +34,7 @@ module MCP
subclass.instance_variable_set(:@input_schema_value, nil)
subclass.instance_variable_set(:@output_schema_value, nil)
subclass.instance_variable_set(:@annotations_value, nil)
subclass.instance_variable_set(:@meta_value, nil)
end
def tool_name(value = NOT_SET)
@ -90,6 +93,14 @@ module MCP
end
end
def meta(value = NOT_SET)
if value == NOT_SET
@meta_value
else
@meta_value = value
end
end
def annotations(hash = NOT_SET)
if hash == NOT_SET
@annotations_value
@ -98,12 +109,13 @@ module MCP
end
end
def define(name: nil, title: nil, description: nil, input_schema: nil, output_schema: nil, annotations: nil, &block)
def define(name: nil, title: nil, description: nil, input_schema: nil, output_schema: nil, meta: nil, annotations: nil, &block)
Class.new(self) do
tool_name name
title title
description description
input_schema input_schema
meta meta
output_schema output_schema
self.annotations(annotations) if annotations
define_singleton_method(:call, &block) if block

4
test/mcp/server_test.rb
View file

@ -10,6 +10,7 @@ module MCP
name: "test_tool",
title: "Test tool",
description: "A test tool",
meta: { foo: "bar" },
)
@tool_that_raises = Tool.define(
@ -195,6 +196,7 @@ module MCP
assert_equal "Test tool", result[:tools][0][:title]
assert_equal "A test tool", result[:tools][0][:description]
assert_equal({ type: "object" }, result[:tools][0][:inputSchema])
assert_equal({ foo: "bar" }, result[:tools][0][:_meta])
assert_instrumentation_data({ method: "tools/list" })
end
@ -211,6 +213,7 @@ module MCP
assert_equal "test_tool", result[:tools][0][:name]
assert_equal "Test tool", result[:tools][0][:title]
assert_equal "A test tool", result[:tools][0][:description]
assert_equal({ foo: "bar" }, result[:tools][0][:_meta])
end
test "#tools_list_handler sets the tools/list handler" do
@ -848,6 +851,7 @@ module MCP
name: "defined_tool",
description: "Defined tool",
input_schema: { type: "object", properties: { message: { type: "string" } }, required: ["message"] },
meta: { foo: "bar" },
) do |message:|
Tool::Response.new(message)
end

52
test/mcp/tool_test.rb
View file

@ -15,6 +15,9 @@ module MCP
read_only_hint: true,
title: "Test Tool",
)
meta(
foo: "bar",
)
class << self
def call(message:, server_context: nil)
@ -52,6 +55,14 @@ module MCP
assert_equal expected_annotations, tool.to_h[:annotations]
end
test "#to_h includes meta when present" do
tool = TestTool
expected_meta = {
foo: "bar",
}
assert_equal expected_meta, tool.to_h[:_meta]
end
test "#call invokes the tool block and returns the response" do
tool = TestTool
response = tool.call(message: "test")
@ -152,6 +163,23 @@ module MCP
assert_equal({ destructiveHint: true, idempotentHint: false, openWorldHint: true, readOnlyHint: true, title: "Mock Tool" }, tool.annotations_value.to_h)
end
test ".define allows definition of tools with meta" do
tool = Tool.define(
name: "mock_tool",
title: "Mock Tool",
description: "a mock tool for testing",
meta: { foo: "bar" },
) do |_|
Tool::Response.new([{ type: "text", content: "OK" }])
end
assert_equal "mock_tool", tool.name_value
assert_equal "Mock Tool", tool.title
assert_equal "a mock tool for testing", tool.description
assert_equal tool.input_schema, Tool::InputSchema.new
assert_equal({ foo: "bar" }, tool.meta_value)
end
test "Tool class method annotations can be set and retrieved" do
class AnnotationsTestTool < Tool
tool_name "annotations_test"
@ -180,6 +208,30 @@ module MCP
assert_equal "Updated", tool.annotations_value.title
end
test "Tool class method meta can be set and retrieved" do
class MetaTestTool < Tool
tool_name "meta_test"
meta(foo: "bar")
end
tool = MetaTestTool
assert_instance_of Hash, tool.meta_value
assert_equal "bar", tool.meta_value[:foo]
end
test "Tool class method meta can be updated" do
class UpdatableMetaTool < Tool
tool_name "updatable_meta"
end
tool = UpdatableMetaTool
tool.meta(foo: "baz")
assert_equal({ foo: "baz" }, tool.meta_value)
tool.meta(foo: "qux")
assert_equal({ foo: "qux" }, tool.meta_value)
end
test "#call with Sorbet typed tools invokes the tool block and returns the response" do
class TypedTestTool < Tool
tool_name "test_tool"