diff --git a/lua/avante/providers/openai.lua b/lua/avante/providers/openai.lua
index b00d8b6..a29ac4d 100644
--- a/lua/avante/providers/openai.lua
+++ b/lua/avante/providers/openai.lua
@@ -27,21 +27,25 @@ function M.transform_tool(tool)
     }
     if not field.optional then table.insert(required, field.name) end
   end
-  local res = {
-    type = "function",
-    ["function"] = {
-      name = tool.name,
-      description = tool.description,
-    },
-  }
-  if vim.tbl_count(input_schema_properties) > 0 then
-    res["function"].parameters = {
+  ---@type AvanteOpenAIToolFunctionParameters
+  local parameters = nil
+  if not vim.tbl_isempty(input_schema_properties) then
+    parameters = {
       type = "object",
       properties = input_schema_properties,
       required = required,
       additionalProperties = false,
     }
   end
+  ---@type AvanteOpenAITool
+  local res = {
+    type = "function",
+    ["function"] = {
+      name = tool.name,
+      description = tool.description,
+      parameters = parameters,
+    },
+  }
   return res
 end
 
diff --git a/lua/avante/types.lua b/lua/avante/types.lua
index f44088f..b176e20 100644
--- a/lua/avante/types.lua
+++ b/lua/avante/types.lua
@@ -171,12 +171,12 @@ vim.g.avante_login = vim.g.avante_login
 ---
 ---@class AvanteOpenAIToolFunction
 ---@field name string
----@field description string
----@field parameters AvanteOpenAIToolFunctionParameters
----@field strict boolean
+---@field description string | nil
+---@field parameters AvanteOpenAIToolFunctionParameters | nil
+---@field strict boolean | nil
 ---
 ---@class AvanteOpenAIToolFunctionParameters
----@field type string
+---@field type "object"
 ---@field properties table<string, AvanteOpenAIToolFunctionParameterProperty>
 ---@field required string[]
 ---@field additionalProperties boolean