Document exclude_args

docs/docs.json

@@ -46,10 +46,17 @@
                 "group": "Servers",
                 "pages": [
                     "servers/fastmcp",
-                    "servers/tools",
-                    "servers/resources",
-                    "servers/prompts",
-                    "servers/context",
+                    {
+                        "group": "Core Components",
+                        "hidden": false,
+                        "icon": "toolbox",
+                        "pages": [
+                            "servers/tools",
+                            "servers/resources",
+                            "servers/prompts",
+                            "servers/context"
+                        ]
+                    },
                     "servers/openapi",
                     "servers/proxy",
                     "servers/composition"

docs/servers/tools.mdx

@@ -158,7 +158,7 @@ While FastMCP infers the name and description from your function, you can overri
 @mcp.tool(
     name="find_products",           # Custom tool name for the LLM
     description="Search the product catalog with optional category filtering.", # Custom description
-    tags={"catalog", "search"}      # Optional tags for organization/filtering
+    tags={"catalog", "search"},      # Optional tags for organization/filtering
 )
 def search_products_implementation(query: str, category: str | None = None) -> list[dict]:
     """Internal function description (ignored if description is provided above)."""
@@ -172,6 +172,25 @@ def search_products_implementation(query: str, category: str | None = None) -> l
 - **`tags`**: A set of strings used to categorize the tool. Clients *might* use tags to filter or group available tools.
 
 
+- **`exclude_args`**:  
+    <VersionBadge version="2.6.0" /> 
+    A list of argument names to exclude from the tool schema shown to the LLM. This is useful for arguments that are injected at runtime (such as `state`, `user_id`, or credentials) and should not be exposed to the LLM or client. Only arguments with default values can be excluded; attempting to exclude a required argument will raise an error.
+  
+
+    Example:
+
+    ```python
+    @mcp.tool(
+        name="get_user_details",
+        exclude_args=["user_id"]
+    )
+    def get_user_details(user_id: str = None) -> str:
+        # user_id will be injected by the server, not provided by the LLM
+        ...
+    ```
+
+    With this configuration, `user_id` will not appear in the tool's parameter schema, but can still be set by the server or framework at runtime.
+
 ### Async Tools
 
 FastMCP seamlessly supports both standard (`def`) and asynchronous (`async def`) functions as tools.

src/fastmcp/tools/tool.py

@@ -102,15 +102,12 @@ class Tool(BaseModel):
         type_adapter = get_cached_typeadapter(fn)
         schema = type_adapter.json_schema()
 
+        prune_params: list[str] = []
         context_kwarg = find_kwarg_by_type(fn, kwarg_type=Context)
-        temp_prune_params: list[str] = []
         if context_kwarg:
-            temp_prune_params.append(context_kwarg)
+            prune_params.append(context_kwarg)
         if exclude_args:
-            temp_prune_params.extend(exclude_args)
-        prune_params: list[str] | None = (
-            None if not temp_prune_params else temp_prune_params
-        )
+            prune_params.extend(exclude_args)
 
         schema = compress_schema(schema, prune_params=prune_params)