From 587d4c032ac7b1bded57b68766f656f7eef2c012 Mon Sep 17 00:00:00 2001
From: Andrzej Pomirski
 <167459559+andrzej-pomirski-yohana@users.noreply.github.com>
Date: Wed, 5 Nov 2025 17:57:55 +0100
Subject: [PATCH] fix: do not use references in Zod to JSON Schema

Many LLMs do not support references in the JSON Schemas for tool inputs/outputs and if they do, they mostly only support root-level references. Schemas produced with Zod to JSON Schema do not comply with this restriction thus, if using strict tool calling (e.g. in OpenAI), the request fails.
---
 src/server/mcp.ts | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/server/mcp.ts b/src/server/mcp.ts
index 015f518a1..6af855f68 100644
--- a/src/server/mcp.ts
+++ b/src/server/mcp.ts
@@ -105,7 +105,8 @@ export class McpServer {
                             inputSchema: tool.inputSchema
                                 ? (zodToJsonSchema(tool.inputSchema, {
                                       strictUnions: true,
-                                      pipeStrategy: 'input'
+                                      pipeStrategy: 'input',
+                                      $refStrategy: 'none'
                                   }) as Tool['inputSchema'])
                                 : EMPTY_OBJECT_JSON_SCHEMA,
                             annotations: tool.annotations,
@@ -115,7 +116,8 @@ export class McpServer {
                         if (tool.outputSchema) {
                             toolDefinition.outputSchema = zodToJsonSchema(tool.outputSchema, {
                                 strictUnions: true,
-                                pipeStrategy: 'output'
+                                pipeStrategy: 'output',
+                                $refStrategy: 'none'
                             }) as Tool['outputSchema'];
                         }