diff --git a/internal/mcp/schema_test.go b/internal/mcp/schema_test.go
new file mode 100644
index 00000000..1fbca562
--- /dev/null
+++ b/internal/mcp/schema_test.go
@@ -0,0 +1,287 @@
+package mcp
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNormalizeInputSchema_NilSchema(t *testing.T) {
+	result := NormalizeInputSchema(nil, "my-tool")
+
+	assert.Equal(t, map[string]interface{}{
+		"type":       "object",
+		"properties": map[string]interface{}{},
+	}, result)
+}
+
+func TestNormalizeInputSchema_AllBranches(t *testing.T) {
+	tests := []struct {
+		name     string
+		schema   map[string]interface{}
+		expected map[string]interface{}
+	}{
+		{
+			// No type, no properties → empty object schema
+			name:   "empty schema returns default empty object schema",
+			schema: map[string]interface{}{},
+			expected: map[string]interface{}{
+				"type":       "object",
+				"properties": map[string]interface{}{},
+			},
+		},
+		{
+			// No type, has properties → add type "object", preserve all fields
+			name: "schema without type but with properties adds object type",
+			schema: map[string]interface{}{
+				"properties": map[string]interface{}{
+					"query": map[string]interface{}{"type": "string"},
+				},
+			},
+			expected: map[string]interface{}{
+				"type": "object",
+				"properties": map[string]interface{}{
+					"query": map[string]interface{}{"type": "string"},
+				},
+			},
+		},
+		{
+			// Non-"object" type string → returned as-is
+			name: "string type schema returned as-is",
+			schema: map[string]interface{}{
+				"type": "string",
+			},
+			expected: map[string]interface{}{
+				"type": "string",
+			},
+		},
+		{
+			// Non-"object" type string with items → returned as-is
+			name: "array type schema returned as-is",
+			schema: map[string]interface{}{
+				"type":  "array",
+				"items": map[string]interface{}{"type": "string"},
+			},
+			expected: map[string]interface{}{
+				"type":  "array",
+				"items": map[string]interface{}{"type": "string"},
+			},
+		},
+		{
+			// Non-string type value → returned as-is
+			name: "non-string type value returned as-is",
+			schema: map[string]interface{}{
+				"type": 42,
+			},
+			expected: map[string]interface{}{
+				"type": 42,
+			},
+		},
+		{
+			// Object type, has properties → returned as-is
+			name: "object schema with properties returned as-is",
+			schema: map[string]interface{}{
+				"type": "object",
+				"properties": map[string]interface{}{
+					"owner": map[string]interface{}{"type": "string"},
+				},
+			},
+			expected: map[string]interface{}{
+				"type": "object",
+				"properties": map[string]interface{}{
+					"owner": map[string]interface{}{"type": "string"},
+				},
+			},
+		},
+		{
+			// Object type, only additionalProperties (no properties key) → returned as-is
+			name: "object schema with only additionalProperties returned as-is",
+			schema: map[string]interface{}{
+				"type":                 "object",
+				"additionalProperties": true,
+			},
+			expected: map[string]interface{}{
+				"type":                 "object",
+				"additionalProperties": true,
+			},
+		},
+		{
+			// Object type, both properties and additionalProperties → returned as-is
+			name: "object schema with properties and additionalProperties returned as-is",
+			schema: map[string]interface{}{
+				"type": "object",
+				"properties": map[string]interface{}{
+					"name": map[string]interface{}{"type": "string"},
+				},
+				"additionalProperties": false,
+			},
+			expected: map[string]interface{}{
+				"type": "object",
+				"properties": map[string]interface{}{
+					"name": map[string]interface{}{"type": "string"},
+				},
+				"additionalProperties": false,
+			},
+		},
+		{
+			// Object type, missing both properties and additionalProperties → add empty properties
+			name: "object type without properties gets empty properties added",
+			schema: map[string]interface{}{
+				"type": "object",
+			},
+			expected: map[string]interface{}{
+				"type":       "object",
+				"properties": map[string]interface{}{},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := NormalizeInputSchema(tt.schema, "test-tool")
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+// TestNormalizeInputSchema_PreservesExtraFields verifies that extra fields like
+// "required", "description", and "$schema" are preserved in copy paths.
+func TestNormalizeInputSchema_PreservesExtraFields(t *testing.T) {
+	t.Run("no-type schema with properties preserves required and description", func(t *testing.T) {
+		schema := map[string]interface{}{
+			"description": "A tool that does things",
+			"properties": map[string]interface{}{
+				"owner": map[string]interface{}{"type": "string"},
+				"repo":  map[string]interface{}{"type": "string"},
+			},
+			"required": []interface{}{"owner", "repo"},
+		}
+
+		result := NormalizeInputSchema(schema, "test-tool")
+
+		assert.Equal(t, "object", result["type"])
+		assert.Equal(t, "A tool that does things", result["description"])
+		assert.Equal(t, []interface{}{"owner", "repo"}, result["required"])
+		assert.NotNil(t, result["properties"])
+	})
+
+	t.Run("object schema without properties preserves required and description", func(t *testing.T) {
+		schema := map[string]interface{}{
+			"type":        "object",
+			"description": "Schema with required but no properties",
+			"required":    []interface{}{"name"},
+		}
+
+		result := NormalizeInputSchema(schema, "test-tool")
+
+		assert.Equal(t, "object", result["type"])
+		assert.Equal(t, "Schema with required but no properties", result["description"])
+		assert.Equal(t, []interface{}{"name"}, result["required"])
+		assert.Equal(t, map[string]interface{}{}, result["properties"])
+	})
+}
+
+// TestNormalizeInputSchema_DoesNotMutateOriginal verifies that the original schema
+// is never modified, only a copy is returned for mutating branches.
+func TestNormalizeInputSchema_DoesNotMutateOriginal(t *testing.T) {
+	t.Run("nil schema does not panic and returns new map", func(t *testing.T) {
+		result := NormalizeInputSchema(nil, "tool")
+		assert.NotNil(t, result)
+	})
+
+	t.Run("no-type schema with properties is not mutated", func(t *testing.T) {
+		original := map[string]interface{}{
+			"properties": map[string]interface{}{
+				"query": map[string]interface{}{"type": "string"},
+			},
+		}
+		_, hadType := original["type"]
+
+		NormalizeInputSchema(original, "test-tool")
+
+		_, nowHasType := original["type"]
+		assert.Equal(t, hadType, nowHasType, "original should not gain a type field")
+		assert.Len(t, original, 1, "original should still have only one key")
+	})
+
+	t.Run("object schema without properties is not mutated", func(t *testing.T) {
+		original := map[string]interface{}{
+			"type": "object",
+		}
+		_, hadProperties := original["properties"]
+
+		NormalizeInputSchema(original, "test-tool")
+
+		_, nowHasProperties := original["properties"]
+		assert.Equal(t, hadProperties, nowHasProperties, "original should not gain a properties field")
+		assert.Len(t, original, 1, "original should still have only one key")
+	})
+
+	t.Run("returned map is a different reference than original for mutating branches", func(t *testing.T) {
+		original := map[string]interface{}{
+			"type": "object",
+		}
+
+		result := NormalizeInputSchema(original, "test-tool")
+
+		// Verify result is a distinct map (modifying result should not affect original)
+		result["extra"] = "value"
+		_, hasExtra := original["extra"]
+		assert.False(t, hasExtra, "modifying the result should not affect the original")
+	})
+}
+
+// TestNormalizeInputSchema_ToolNameVariants verifies that the toolName parameter
+// is accepted in various forms without affecting normalization logic.
+func TestNormalizeInputSchema_ToolNameVariants(t *testing.T) {
+	schema := map[string]interface{}{
+		"type": "object",
+	}
+	expected := map[string]interface{}{
+		"type":       "object",
+		"properties": map[string]interface{}{},
+	}
+
+	toolNames := []string{
+		"simple",
+		"",
+		"server___tool-name",
+		"tool with spaces",
+		"tool/with/slashes",
+		"very-long-tool-name-that-exceeds-normal-length-limits-for-mcp-tool-names",
+	}
+
+	for _, name := range toolNames {
+		t.Run("tool name: "+name, func(t *testing.T) {
+			result := NormalizeInputSchema(schema, name)
+			assert.Equal(t, expected, result, "normalization result should not depend on toolName")
+		})
+	}
+}
+
+// TestNormalizeInputSchema_DeepNestedSchema verifies that deeply nested
+// schemas are handled correctly without modification.
+func TestNormalizeInputSchema_DeepNestedSchema(t *testing.T) {
+	deep := map[string]interface{}{
+		"type": "object",
+		"properties": map[string]interface{}{
+			"nested": map[string]interface{}{
+				"type": "object",
+				"properties": map[string]interface{}{
+					"deeper": map[string]interface{}{
+						"type": "array",
+						"items": map[string]interface{}{
+							"type": "string",
+						},
+					},
+				},
+			},
+		},
+		"required": []interface{}{"nested"},
+	}
+
+	result := NormalizeInputSchema(deep, "deep-tool")
+
+	// Schema already valid, should be returned as-is
+	assert.Equal(t, deep, result)
+}