diff --git a/pyproject.toml b/pyproject.toml
index 1ff2303..28adf7c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,6 +5,7 @@ description = "MCP (Model Context Protocol) server for Appwrite"
 readme = "README.md"
 requires-python = ">=3.12"
 dependencies = [
+    "anyio>=4.0.0",
     "appwrite>=21.0.0,<22",
     "docstring-parser>=0.16",
     "mcp[cli]>=1.12.0",
diff --git a/src/mcp_server_appwrite/operator.py b/src/mcp_server_appwrite/operator.py
index 681c059..db277af 100644
--- a/src/mcp_server_appwrite/operator.py
+++ b/src/mcp_server_appwrite/operator.py
@@ -2,6 +2,7 @@
 
 import json
 import re
+import threading
 import time
 from collections import OrderedDict
 from dataclasses import dataclass
@@ -74,12 +75,15 @@ class ResultStore:
     def __init__(self, max_size: int = RESULT_STORE_SIZE):
         self._entries: OrderedDict[str, StoredResult] = OrderedDict()
         self._max_size = max_size
+        self._lock = threading.Lock()
 
     def get(self, result_id: str) -> StoredResult | None:
-        return self._entries.get(result_id)
+        with self._lock:
+            return self._entries.get(result_id)
 
     def list(self) -> list[StoredResult]:
-        return list(self._entries.values())
+        with self._lock:
+            return list(self._entries.values())
 
     def save(
         self, tool_name: str, content: list[ToolContent], text: str
@@ -91,9 +95,10 @@ def save(
             text=text,
             tool_name=tool_name,
         )
-        self._entries[result.result_id] = result
-        while len(self._entries) > self._max_size:
-            self._entries.popitem(last=False)
+        with self._lock:
+            self._entries[result.result_id] = result
+            while len(self._entries) > self._max_size:
+                self._entries.popitem(last=False)
         return result
 
 
diff --git a/src/mcp_server_appwrite/server.py b/src/mcp_server_appwrite/server.py
index c6ded89..71ae1a9 100644
--- a/src/mcp_server_appwrite/server.py
+++ b/src/mcp_server_appwrite/server.py
@@ -27,6 +27,7 @@
 import httpx
 import mcp.server.stdio
 import mcp.types as types
+from anyio import to_thread
 from appwrite.client import Client
 from appwrite.enums.browser import Browser
 from appwrite.exception import AppwriteException
@@ -988,7 +989,9 @@ async def handle_call_tool(
         try:
             if not operator.has_public_tool(name):
                 raise ValueError(f"Tool {name} not found")
-            result = operator.execute_public_tool(name, arguments)
+            result = await _execute_public_tool_for_transport(
+                operator, name, arguments, transport
+            )
         except Exception:
             telemetry.record_request("tools/call", "error", time.monotonic() - start)
             raise
@@ -1031,6 +1034,23 @@ async def handle_read_resource(uri) -> list[ReadResourceContents]:
     return server
 
 
+async def _execute_public_tool_for_transport(
+    operator: Operator,
+    name: str,
+    arguments: dict | None,
+    transport: str,
+) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+    if transport != "http":
+        return operator.execute_public_tool(name, arguments)
+
+    # The Appwrite Python SDK, docs embedding client, context discovery, and URL
+    # upload fetches are synchronous. Running them on the ASGI event-loop thread
+    # can make even /healthz stop responding while a tool call is slow or stuck.
+    return await to_thread.run_sync(
+        operator.execute_public_tool, name, arguments, abandon_on_cancel=True
+    )
+
+
 def _emit_initialize(server: Server) -> None:
     """Emit an ``mcp.initializations`` event and refresh active-user/client tracking
     for the current session. Deduped per session in the telemetry layer. Best-effort:
diff --git a/tests/unit/test_operator.py b/tests/unit/test_operator.py
index e20d4d7..dcbadd5 100644
--- a/tests/unit/test_operator.py
+++ b/tests/unit/test_operator.py
@@ -1,8 +1,9 @@
 import unittest
+from concurrent.futures import ThreadPoolExecutor
 
 import mcp.types as types
 
-from mcp_server_appwrite.operator import CATALOG_URI, Operator
+from mcp_server_appwrite.operator import CATALOG_URI, Operator, ResultStore
 from mcp_server_appwrite.tool_manager import ToolManager
 
 
@@ -329,5 +330,31 @@ def test_store_results_false_returns_image_inline(self):
         self.assertEqual(result[0].mimeType, "image/png")
 
 
+class ResultStoreTests(unittest.TestCase):
+    def test_concurrent_save_and_list_are_thread_safe(self):
+        store = ResultStore(max_size=50)
+        content = [types.TextContent(type="text", text="ok")]
+
+        def save_many():
+            for index in range(500):
+                store.save("tables_db_list", content, f"result {index}")
+
+        def list_many():
+            for _ in range(500):
+                store.list()
+
+        with ThreadPoolExecutor(max_workers=4) as executor:
+            futures = [
+                executor.submit(save_many),
+                executor.submit(save_many),
+                executor.submit(list_many),
+                executor.submit(list_many),
+            ]
+            for future in futures:
+                future.result()
+
+        self.assertLessEqual(len(store.list()), 50)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/unit/test_server.py b/tests/unit/test_server.py
index 364b3af..0b646a5 100644
--- a/tests/unit/test_server.py
+++ b/tests/unit/test_server.py
@@ -1,8 +1,10 @@
+import asyncio
 import base64
 import io
 import os
 import sys
 import tempfile
+import time
 import unittest
 from pathlib import Path
 from unittest.mock import Mock, patch
@@ -15,6 +17,7 @@
 from mcp_server_appwrite.server import (
     _coerce_argument,
     _configure_uploads,
+    _execute_public_tool_for_transport,
     _format_tool_result,
     _prepare_arguments,
     _validate_service,
@@ -107,6 +110,29 @@ def test_build_instructions_are_transport_specific(self):
         self.assertIn("Large results are stored as resources", stdio)
         self.assertIn("returns tool results inline", http)
 
+    def test_http_tool_execution_does_not_block_event_loop(self):
+        class BlockingOperator:
+            def execute_public_tool(self, name, arguments):
+                time.sleep(0.2)
+                return [types.TextContent(type="text", text="ok")]
+
+        async def run_check():
+            start = time.monotonic()
+            task = asyncio.create_task(
+                _execute_public_tool_for_transport(
+                    BlockingOperator(), "appwrite_call_tool", {}, "http"
+                )
+            )
+
+            await asyncio.sleep(0.01)
+
+            self.assertLess(time.monotonic() - start, 0.1)
+            self.assertFalse(task.done())
+            result = await task
+            self.assertEqual(result[0].text, "ok")
+
+        asyncio.run(run_check())
+
     def test_coerce_input_file_from_path(self):
         with tempfile.NamedTemporaryFile(suffix=".txt") as handle:
             coerced = _coerce_argument("file", handle.name, InputFile)
diff --git a/uv.lock b/uv.lock
index c90d1aa..f7a58b8 100644
--- a/uv.lock
+++ b/uv.lock
@@ -642,6 +642,7 @@ name = "mcp-server-appwrite"
 version = "0.8.6"
 source = { editable = "." }
 dependencies = [
+    { name = "anyio" },
     { name = "appwrite" },
     { name = "docstring-parser" },
     { name = "httpx" },
@@ -676,6 +677,7 @@ dev = [
 
 [package.metadata]
 requires-dist = [
+    { name = "anyio", specifier = ">=4.0.0" },
     { name = "appwrite", specifier = ">=21.0.0,<22" },
     { name = "argon2-cffi", marker = "extra == 'integration'", specifier = ">=23.1.0" },
     { name = "bcrypt", marker = "extra == 'integration'", specifier = ">=4.1.2" },