1 files changed, 68 insertions, 0 deletions
diff --git a/packages/core/src/tools/mcp-client.ts b/packages/core/src/tools/mcp-client.ts
index 26244d9e..9a35b84e 100644
--- a/packages/core/src/tools/mcp-client.ts
+++ b/packages/core/src/tools/mcp-client.ts
@@ -417,6 +417,65 @@ export async function connectAndDiscover(
 }
 
 /**
+ * Recursively validates that a JSON schema and all its nested properties and
+ * items have a `type` defined.
+ *
+ * @param schema The JSON schema to validate.
+ * @returns `true` if the schema is valid, `false` otherwise.
+ *
+ * @visiblefortesting
+ */
+export function hasValidTypes(schema: unknown): boolean {
+  if (typeof schema !== 'object' || schema === null) {
+    // Not a schema object we can validate, or not a schema at all.
+    // Treat as valid as it has no properties to be invalid.
+    return true;
+  }
+
+  const s = schema as Record<string, unknown>;
+
+  if (!s.type) {
+    // These keywords contain an array of schemas that should be validated.
+    //
+    // If no top level type was given, then they must each have a type.
+    let hasSubSchema = false;
+    const schemaArrayKeywords = ['anyOf', 'allOf', 'oneOf'];
+    for (const keyword of schemaArrayKeywords) {
+      const subSchemas = s[keyword];
+      if (Array.isArray(subSchemas)) {
+        hasSubSchema = true;
+        for (const subSchema of subSchemas) {
+          if (!hasValidTypes(subSchema)) {
+            return false;
+          }
+        }
+      }
+    }
+
+    // If the node itself is missing a type and had no subschemas, then it isn't valid.
+    if (!hasSubSchema) return false;
+  }
+
+  if (s.type === 'object' && s.properties) {
+    if (typeof s.properties === 'object' && s.properties !== null) {
+      for (const prop of Object.values(s.properties)) {
+        if (!hasValidTypes(prop)) {
+          return false;
+        }
+      }
+    }
+  }
+
+  if (s.type === 'array' && s.items) {
+    if (!hasValidTypes(s.items)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/**
  * Discovers and sanitizes tools from a connected MCP client.
  * It retrieves function declarations from the client, filters out disabled tools,
  * generates valid names for them, and wraps them in `DiscoveredMCPTool` instances.
@@ -448,6 +507,15 @@ export async function discoverTools(
           continue;
         }
 
+        if (!hasValidTypes(funcDecl.parametersJsonSchema)) {
+          console.warn(
+            `Skipping tool '${funcDecl.name}' from MCP server '${mcpServerName}' ` +
+              `because it has missing types in its parameter schema. Please file an ` +
+              `issue with the owner of the MCP server.`,
+          );
+          continue;
+        }
+
         discoveredTools.push(
           new DiscoveredMCPTool(
             mcpCallableTool,