From d0d53cc5a7700b03cde018173c51c4577b26526c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Publio=20Estupi=C3=B1=C3=A1n?= <publinchi@gmail.com>
Date: Sat, 11 Apr 2026 20:09:09 -0500
Subject: [PATCH] fix(mcp): preserve JSON Schema types and required fields in
 createSchemaModel

The createSchemaModel function was mapping every MCP tool property to
z.any(), discarding all type information. This caused two problems:

1. The required array from inputSchema was ignored, making all parameters
   optional. LLMs would then call tools with empty arguments {}.

2. Type information (string, integer, boolean, array, object, anyOf) was
   lost. When converted back to JSON Schema for the OpenAI API, property
   type keys were missing, causing strict mode rejections.

Fixes:
- Add jsonSchemaToZod() helper that maps JSON Schema types to proper Zod
  types (z.string, z.number, z.boolean, z.array, z.record) and handles
  anyOf/nullable patterns.
- Read the required array from inputSchema and mark non-required fields
  as .optional() in the resulting Zod schema.

Fixes #5109

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 packages/components/nodes/tools/MCP/core.ts | 38 +++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/packages/components/nodes/tools/MCP/core.ts b/packages/components/nodes/tools/MCP/core.ts
index 16f9f050f88..488b8bf9cb6 100644
--- a/packages/components/nodes/tools/MCP/core.ts
+++ b/packages/components/nodes/tools/MCP/core.ts
@@ -177,6 +177,37 @@ export async function MCPTool({
     )
 }
 
+function jsonSchemaToZod(schema: unknown): ZodTypeAny {
+    if (!schema || typeof schema !== 'object') return z.any()
+    const s = schema as Record<string, unknown>
+
+    if (Array.isArray(s['anyOf'])) {
+        const types = (s['anyOf'] as unknown[]).filter((t) => {
+            if (!t || typeof t !== 'object') return false
+            return (t as Record<string, unknown>)['type'] !== 'null'
+        })
+        if (types.length === 0) return z.any().nullable().optional()
+        if (types.length === 1) return jsonSchemaToZod(types[0]).nullable().optional()
+        return z.any().nullable().optional()
+    }
+
+    switch (s['type']) {
+        case 'string':
+            return z.string()
+        case 'integer':
+        case 'number':
+            return z.number()
+        case 'boolean':
+            return z.boolean()
+        case 'array':
+            return z.array(s['items'] ? jsonSchemaToZod(s['items']) : z.any())
+        case 'object':
+            return z.record(z.any())
+        default:
+            return z.any()
+    }
+}
+
 function createSchemaModel(
     inputSchema: {
         type: 'object'
@@ -187,8 +218,11 @@ function createSchemaModel(
         throw new Error('Invalid schema type or missing properties')
     }
 
-    const schemaProperties = Object.entries(inputSchema.properties).reduce((acc, [key]) => {
-        acc[key] = z.any()
+    const required = Array.isArray(inputSchema['required']) ? (inputSchema['required'] as string[]) : []
+
+    const schemaProperties = Object.entries(inputSchema.properties).reduce((acc, [key, value]) => {
+        const zodType = jsonSchemaToZod(value)
+        acc[key] = required.includes(key) ? zodType : zodType.optional()
         return acc
     }, {} as Record<string, ZodTypeAny>)