diff --git a/plugin/src/Types.lua b/plugin/src/Types.lua
index f182d60a..3d866a1a 100644
--- a/plugin/src/Types.lua
+++ b/plugin/src/Types.lua
@@ -1,21 +1,68 @@
 local t = require(script.Parent.Parent.t)
 
 local DevSettings = require(script.Parent.DevSettings)
+local strict = require(script.Parent.strict)
 
-local VirtualValue = t.interface({
+local RbxId = t.string
+
+local ApiValue = t.interface({
 	Type = t.string,
 	Value = t.optional(t.any),
 })
 
-local VirtualMetadata = t.interface({
+local ApiInstanceMetadata = t.interface({
 	ignoreUnknownInstances = t.optional(t.boolean),
 })
 
-local VirtualInstance = t.interface({
+local ApiInstance = t.interface({
 	Name = t.string,
 	ClassName = t.string,
-	Properties = t.map(t.string, VirtualValue),
-	Metadata = t.optional(VirtualMetadata)
+	Properties = t.map(t.string, ApiValue),
+	Metadata = t.optional(ApiInstanceMetadata),
+	Children = t.array(RbxId),
+})
+
+local ApiInstanceUpdate = t.interface({
+	id = RbxId,
+	changedName = t.optional(t.string),
+	changedClassName = t.optional(t.string),
+	changedProperties = t.map(t.string, ApiValue),
+	changedMetadata = t.optional(ApiInstanceMetadata),
+})
+
+local ApiSubscribeMessage = t.interface({
+	removedInstances = t.array(RbxId),
+	addedInstances = t.map(RbxId, ApiInstance),
+	updatedInstances = t.array(ApiInstanceUpdate),
+})
+
+local ApiInfoResponse = t.interface({
+	sessionId = t.string,
+	serverVersion = t.string,
+	protocolVersion = t.number,
+	expectedPlaceIds = t.optional(t.array(t.number)),
+	rootInstanceId = RbxId,
+})
+
+local ApiReadResponse = t.interface({
+	sessionId = t.string,
+	messageCursor = t.number,
+	instances = t.map(RbxId, ApiInstance),
+})
+
+local ApiSubscribeResponse = t.interface({
+	sessionId = t.string,
+	messageCursor = t.number,
+	messages = t.array(ApiSubscribeMessage),
+})
+
+local ApiError = t.interface({
+	kind = t.union(
+		t.literal("NotFound"),
+		t.literal("BadRequest"),
+		t.literal("InternalError")
+	),
+	details = t.string,
 })
 
 local function ifEnabled(innerCheck)
@@ -28,9 +75,22 @@ local function ifEnabled(innerCheck)
 	end
 end
 
-return {
+return strict("Types", {
 	ifEnabled = ifEnabled,
-	VirtualInstance = VirtualInstance,
-	VirtualMetadata = VirtualMetadata,
-	VirtualValue = VirtualValue,
-}
\ No newline at end of file
+
+	ApiInfoResponse = ApiInfoResponse,
+	ApiReadResponse = ApiReadResponse,
+	ApiSubscribeResponse = ApiSubscribeResponse,
+	ApiError = ApiError,
+
+	ApiInstance = ApiInstance,
+	ApiInstanceMetadata = ApiInstanceMetadata,
+	ApiSubscribeMessage = ApiSubscribeMessage,
+	ApiValue = ApiValue,
+	RbxId = RbxId,
+
+	-- Deprecated aliases during transition
+	VirtualInstance = ApiInstance,
+	VirtualMetadata = ApiInstanceMetadata,
+	VirtualValue = ApiValue,
+})
\ No newline at end of file
diff --git a/plugin/src/strict.lua b/plugin/src/strict.lua
new file mode 100644
index 00000000..239c84a2
--- /dev/null
+++ b/plugin/src/strict.lua
@@ -0,0 +1,24 @@
+local function strictInner(name, target)
+	assert(type(name) == "string", "Argument #1 to `strict` must be a string or the table to modify")
+	assert(type(target) == "table", "Argument #2 to `strict` must be nil or the table to modify")
+
+	setmetatable(target, {
+		__index = function(_, key)
+			error(("%q is not a valid member of strict table %q"):format(tostring(key), name), 2)
+		end,
+
+		__newindex = function()
+			error(("Strict table %q is read-only"):format(name), 2)
+		end,
+	})
+
+	return target
+end
+
+return function(nameOrTarget, target)
+	if type(nameOrTarget) == "string" then
+		return strictInner(nameOrTarget, target)
+	else
+		return strictInner("<unnamed table>", target)
+	end
+end
\ No newline at end of file