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Merge pull request #369 from koic/switch_to_json_schemer

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Speed Up `Tool::Schema` Validation by 5x to 100x
This commit is contained in:
Koichi ITO 2026-06-13 20:13:00 +09:00 • committed by GitHub
commit 39676bc93c
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7 changed files with 81 additions and 42 deletions
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4
lib/mcp/tool/input_schema.rb
View file

@ -12,9 +12,9 @@ module MCP
end
def missing_required_arguments(arguments)
return [] unless schema[:required].is_a?(Array)
return [] unless @schema[:required].is_a?(Array)
(schema[:required] - arguments.keys.map(&:to_s))
(@schema[:required] - arguments.keys.map(&:to_s))
end
def validate_arguments(arguments)

57
lib/mcp/tool/schema.rb
View file

@ -1,7 +1,7 @@
# frozen_string_literal: true
require "digest"
require "json-schema"
require "json_schemer"
module MCP
class Tool
@ -38,11 +38,10 @@ module MCP
# JSON Schema 2020-12 is the default dialect for MCP schema definitions
# per MCP 2025-11-25 (SEP-1613). Note: emission only — runtime validation
# is still performed against the JSON Schema draft-04 metaschema because
# the `json-schema` gem does not yet support 2020-12.
# is still performed against the JSON Schema draft-04 metaschema.
JSON_SCHEMA_2020_12_URI = "https://json-schema.org/draft/2020-12/schema"
attr_reader :schema
DRAFT4_META_SCHEMA_URI = "http://json-schema.org/draft-04/schema#"
def initialize(schema = {})
@schema = JSON.parse(JSON.dump(schema), symbolize_names: true)
@ -51,7 +50,7 @@ module MCP
end
def ==(other)
other.is_a?(self.class) && schema == other.schema
other.is_a?(self.class) && @schema == other.instance_variable_get(:@schema)
end
def to_h
@ -62,8 +61,38 @@ module MCP
private
def stringify(obj)
case obj
when Hash
obj.each_with_object({}) { |(k, v), h| h[k.to_s] = stringify(v) }
when Array
obj.map { |v| stringify(v) }
when Symbol
obj.to_s
else
obj
end
end
# Lazily built so a cache hit in `validate_schema!` avoids the schemer construction cost.
# Memoized per Schema instance because schema content is fixed at construction,
# so the compiled schemer is reusable across many `fully_validate` calls.
#
# `format: false` preserves the legacy behavior of the previous `json-schema` based implementation,
# which did not enforce `format` keywords. `RegexpError` from a malformed `pattern` is re-raised as
# `ArgumentError` so callers see the same exception class they used to.
def schemer
@schemer ||= JSONSchemer.schema(
stringify(schema_for_validation),
meta_schema: DRAFT4_META_SCHEMA_URI,
format: false,
)
rescue RegexpError => e
raise ArgumentError, "Invalid JSON Schema: #{e.message}"
end
def fully_validate(data)
JSON::Validator.fully_validate(schema_for_validation, data)
schemer.validate(stringify(data)).map { |validation_error| validation_error.fetch("error") }
end
def validate_schema!
@ -75,16 +104,7 @@ module MCP
key = Digest::SHA256.hexdigest(JSON.generate(target, max_nesting: false))
return if VALIDATION_CACHE.validated?(key)
gem_path = File.realpath(Gem.loaded_specs["json-schema"].full_gem_path)
schema_reader = JSON::Schema::Reader.new(
accept_uri: false,
accept_file: ->(path) { File.realpath(path.to_s).start_with?(gem_path) },
)
metaschema_path = Pathname.new(JSON::Validator.validator_for_name("draft4").metaschema)
# Converts metaschema to a file URI for cross-platform compatibility
metaschema_uri = JSON::Util::URI.file_uri(metaschema_path.expand_path.cleanpath.to_s.tr("\\", "/"))
metaschema = metaschema_uri.to_s
errors = JSON::Validator.fully_validate(metaschema, target, schema_reader: schema_reader)
errors = schemer.validate_schema.map { |validation_error| validation_error.fetch("error") }
if errors.any?
raise ArgumentError, "Invalid JSON Schema: #{errors.join(", ")}"
end
@ -92,9 +112,8 @@ module MCP
VALIDATION_CACHE.store(key)
end
# The `json-schema` gem's draft-04 validator cannot resolve newer or unknown `$schema`
# dialect URIs. Strip the top-level `$schema` before validation so a dialect URI
# (whether SDK-injected by `to_h` or user-supplied) does not break the validator.
# `json_schemer` is pinned to the draft-04 metaschema, so strip top-level `$schema` before validation:
# this preserves the legacy behavior of ignoring the advertised dialect URI when the SDK validates schemas.
def schema_for_validation
return @schema unless @schema.key?(:"$schema")

2
mcp.gemspec
View file

@ -30,5 +30,5 @@ Gem::Specification.new do |spec|
spec.executables = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
spec.require_paths = ["lib"]
spec.add_dependency("json-schema", ">= 4.1")
spec.add_dependency("json_schemer", ">= 2.4")
end

30
test/mcp/tool/input_schema_test.rb
View file

@ -7,7 +7,7 @@ module MCP
class InputSchemaTest < ActiveSupport::TestCase
test "required arguments are converted to strings" do
input_schema = InputSchema.new(properties: { message: { type: "string" } }, required: [:message])
assert_equal ["message"], input_schema.schema[:required]
assert_equal ["message"], input_schema.to_h[:required]
end
test "to_h returns a hash representation of the input schema" do
@ -139,10 +139,10 @@ module MCP
test "unexpected errors bubble up from validate_arguments" do
schema = InputSchema.new(properties: { foo: { type: "string" } }, required: ["foo"])
JSON::Validator.stub(:fully_validate, ->(*) { raise "unexpected error" }) do
assert_raises(RuntimeError) do
schema.validate_arguments({ foo: "bar" })
end
JSONSchemer::Schema.any_instance.stubs(:validate).raises("unexpected error")
assert_raises(RuntimeError) do
schema.validate_arguments(foo: "bar")
end
end
@ -200,6 +200,26 @@ module MCP
schema6 = InputSchema.new(properties: { foo: { type: "string" } }, required: ["foo"], additionalProperties: false)
refute_equal schema1, schema6
end
test "format keyword is not enforced (legacy behavior)" do
schema = InputSchema.new(
properties: { email: { type: "string", format: "email" } },
required: ["email"],
)
assert_nil(schema.validate_arguments(email: "not_an_email"))
end
test "invalid pattern raises ArgumentError, not RegexpError" do
error = assert_raises(ArgumentError) do
InputSchema.new(properties: { id: { type: "string", pattern: "[" } })
end
assert_includes error.message, "Invalid JSON Schema"
end
test "Symbol values in arguments are treated as strings" do
schema = InputSchema.new(properties: { foo: { type: "string" } }, required: ["foo"])
assert_nil(schema.validate_arguments(foo: :bar))
end
end
end
end

8
test/mcp/tool/output_schema_test.rb
View file

@ -110,10 +110,10 @@ module MCP
test "unexpected errors bubble up from validate_result" do
schema = OutputSchema.new(properties: { foo: { type: "string" } }, required: ["foo"])
JSON::Validator.stub(:fully_validate, ->(*) { raise "unexpected error" }) do
assert_raises(RuntimeError) do
schema.validate_result({ foo: "bar" })
end
JSONSchemer::Schema.any_instance.stubs(:validate).raises("unexpected error")
assert_raises(RuntimeError) do
schema.validate_result(foo: "bar")
end
end

14
test/mcp/tool/schema_test.rb
View file

@ -10,7 +10,7 @@ module MCP
end
test "validates a schema once and reuses the result for identical schemas" do
JSON::Validator.expects(:fully_validate).once.returns([])
JSONSchemer::Schema.any_instance.expects(:validate_schema).once.returns([])
schema = { properties: { validates_once: { type: "string" } } }
InputSchema.new(schema)
@ -18,7 +18,7 @@ module MCP
end
test "validates distinct schemas separately" do
JSON::Validator.expects(:fully_validate).twice.returns([])
JSONSchemer::Schema.any_instance.expects(:validate_schema).twice.returns([])
InputSchema.new(properties: { distinct_a: { type: "string" } })
InputSchema.new(properties: { distinct_b: { type: "string" } })
@ -64,11 +64,11 @@ module MCP
break
end
JSON::Validator.stub(:fully_validate, []) do
assert_nothing_raised do
InputSchema.new(schema)
InputSchema.new(schema)
end
JSONSchemer::Schema.any_instance.stubs(:validate_schema).returns([])
assert_nothing_raised do
InputSchema.new(schema)
InputSchema.new(schema)
end
end

8
test/mcp/tool_test.rb
View file

@ -167,8 +167,8 @@ module MCP
end
assert_includes error.message, "Invalid JSON Schema"
assert_includes error.message, "#/properties/count/minimum"
assert_includes error.message, "string did not match the following type: number"
assert_includes error.message, "properties/count/minimum"
assert_includes error.message, "number"
end
test ".define allows definition of simple tools with a block" do
@ -431,8 +431,8 @@ module MCP
end
assert_includes error.message, "Invalid JSON Schema"
assert_includes error.message, "#/properties/count/minimum"
assert_includes error.message, "string did not match the following type: number"
assert_includes error.message, "properties/count/minimum"
assert_includes error.message, "number"
end
test "output_schema accepts $ref in schema" do