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fix(jsonschema): root variables object is always a non-nullable "object" #1528

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Merged
asoorm merged 1 commit into from
Jun 8, 2026
Merged

fix(jsonschema): root variables object is always a non-nullable "object" #1528

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10 changes: 6 additions & 4 deletions v2/pkg/engine/jsonschema/variables_schema.go
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Original file line number Diff line number Diff line change
Expand Up @@ -156,10 +156,12 @@ func (v *VariablesSchemaBuilder) EnterVariableDefinition(ref int) {

// GetSchema returns the built schema
func (v *VariablesSchemaBuilder) GetSchema() *JsonSchema {
// If we have required fields, the root schema cannot be nullable
if len(v.schema.Required) > 0 {
v.schema.Nullable = false
}
// The root variables object is always a concrete object and must never be
// nullable: the variables container is either present or omitted, never the
// JSON literal null. Emitting a nullable root (type ["object","null"] under
// JSON Schema 2020-12) breaks strict consumers such as the MCP SDK, which
// require the input schema's type to be exactly "object".
v.schema.Nullable = false
// Attach definitions for any recursive input types referenced via "$ref"
if len(v.defs) > 0 {
v.schema.Defs = v.defs
Expand Down
32 changes: 10 additions & 22 deletions v2/pkg/engine/jsonschema/variables_schema_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -117,10 +117,7 @@ func TestBuildJsonSchema(t *testing.T) {
"type": "object"
}
},
"type": [
"object",
"null"
]
"type": "object"
}`

// Compare actual JSON with expected JSON
Expand Down Expand Up @@ -1362,17 +1359,14 @@ func TestBuildJsonSchema(t *testing.T) {
"type": "object"
}
},
"type": [
"object",
"null"
]
"type": "object"
}`

// Compare actual JSON with expected JSON
assert.JSONEq(t, expectedJSON, string(data), "JSON schema does not match expected structure")
})

t.Run("root schema nullable based on required arguments", func(t *testing.T) {
t.Run("root schema is always a non-nullable object", func(t *testing.T) {
// Define schema with required and optional arguments
schemaSDL := scalarDefinitions + `
schema {
Expand Down Expand Up @@ -1452,7 +1446,10 @@ func TestBuildJsonSchema(t *testing.T) {
data2, err := json.MarshalIndent(schema2, "", " ")
require.NoError(t, err)

// Define expected JSON schema for optional argument case
// Define expected JSON schema for optional argument case.
// Even when every variable is optional, the root variables object stays a
// non-nullable "object": the container is omitted or present, never the
// JSON literal null. Only the individual optional fields are nullable.
expectedJSON2 := `{
"additionalProperties": false,
"properties": {
Expand All @@ -1463,10 +1460,7 @@ func TestBuildJsonSchema(t *testing.T) {
]
}
},
"type": [
"object",
"null"
]
"type": "object"
}`

// Compare actual JSON with expected JSON
Expand Down Expand Up @@ -1553,10 +1547,7 @@ func TestBuildJsonSchema(t *testing.T) {
"type": "object"
}
},
"type": [
"object",
"null"
]
"type": "object"
}`

// Compare actual JSON with expected JSON
Expand Down Expand Up @@ -1624,10 +1615,7 @@ func TestBuildJsonSchema(t *testing.T) {
"description": "ISO-8601 date time format"
}
},
"type": [
"object",
"null"
]
"type": "object"
}`

// Compare actual JSON with expected JSON
Expand Down
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