From f55dac69582000f0bfdae6dbed2d33f2e48087b2 Mon Sep 17 00:00:00 2001
From: centdix <40307056+centdix@users.noreply.github.com>
Date: Mon, 19 Jan 2026 21:24:12 +0100
Subject: [PATCH] fix(mcp): fix empty args format + sanitize tool name (#7615)

* fix empty args format + sanitize tool name

* cleaning
---
 backend/windmill-mcp/src/client/mod.rs  |  4 ++--
 backend/windmill-worker/src/ai/utils.rs | 16 +++++++++++++++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/backend/windmill-mcp/src/client/mod.rs b/backend/windmill-mcp/src/client/mod.rs
index 2364571486..2cac061c5e 100644
--- a/backend/windmill-mcp/src/client/mod.rs
+++ b/backend/windmill-mcp/src/client/mod.rs
@@ -190,7 +190,7 @@ impl McpClient {
         args_str: &str,
     ) -> Result<Option<serde_json::Map<String, serde_json::Value>>> {
         if args_str.trim().is_empty() {
-            return Ok(None);
+            return Ok(Some(serde_json::Map::new()));
         }
 
         let args_value: serde_json::Value =
@@ -198,7 +198,7 @@ impl McpClient {
 
         match args_value {
             serde_json::Value::Object(map) => Ok(Some(map)),
-            serde_json::Value::Null => Ok(None),
+            serde_json::Value::Null => Ok(Some(serde_json::Map::new())),
             _ => Ok(Some(
                 vec![("value".to_string(), args_value)]
                     .into_iter()
diff --git a/backend/windmill-worker/src/ai/utils.rs b/backend/windmill-worker/src/ai/utils.rs
index 5f017a4e75..7bd02af4ff 100644
--- a/backend/windmill-worker/src/ai/utils.rs
+++ b/backend/windmill-worker/src/ai/utils.rs
@@ -351,6 +351,19 @@ pub async fn cleanup_mcp_clients(mcp_clients: HashMap<String, Arc<McpClient>>) {
     }
 }
 
+#[cfg(feature = "mcp")]
+fn sanitize_tool_name_part(s: &str) -> String {
+    s.chars()
+        .map(|c| {
+            if c.is_ascii_alphanumeric() || c == '_' || c == '-' {
+                c
+            } else {
+                '_'
+            }
+        })
+        .collect()
+}
+
 /// Convert raw MCP tools to Windmill Tool format with source tracking
 #[cfg(feature = "mcp")]
 fn convert_mcp_tools_to_windmill_tools(
@@ -361,7 +374,8 @@ fn convert_mcp_tools_to_windmill_tools(
     mcp_tools
         .iter()
         .map(|mcp_tool| {
-            let tool_name = format!("mcp_{}_{}", resource_name, mcp_tool.name);
+            let sanitized_resource_name = sanitize_tool_name_part(resource_name);
+            let tool_name = format!("mcp_{}_{}", sanitized_resource_name, mcp_tool.name);
 
             let mut schema_value = serde_json::to_value(&*mcp_tool.input_schema)
                 .context("Failed to convert MCP schema to JSON value")?;