diff --git a/nanobot/agent/tools/registry.py b/nanobot/agent/tools/registry.py
index 725706dce..99d3ec63a 100644
--- a/nanobot/agent/tools/registry.py
+++ b/nanobot/agent/tools/registry.py
@@ -31,9 +31,36 @@ class ToolRegistry:
         """Check if a tool is registered."""
         return name in self._tools
 
+    @staticmethod
+    def _schema_name(schema: dict[str, Any]) -> str:
+        """Extract a normalized tool name from either OpenAI or flat schemas."""
+        fn = schema.get("function")
+        if isinstance(fn, dict):
+            name = fn.get("name")
+            if isinstance(name, str):
+                return name
+        name = schema.get("name")
+        return name if isinstance(name, str) else ""
+
     def get_definitions(self) -> list[dict[str, Any]]:
-        """Get all tool definitions in OpenAI format."""
-        return [tool.to_schema() for tool in self._tools.values()]
+        """Get tool definitions with stable ordering for cache-friendly prompts.
+
+        Built-in tools are sorted first as a stable prefix, then MCP tools are
+        sorted and appended.
+        """
+        definitions = [tool.to_schema() for tool in self._tools.values()]
+        builtins: list[dict[str, Any]] = []
+        mcp_tools: list[dict[str, Any]] = []
+        for schema in definitions:
+            name = self._schema_name(schema)
+            if name.startswith("mcp_"):
+                mcp_tools.append(schema)
+            else:
+                builtins.append(schema)
+
+        builtins.sort(key=self._schema_name)
+        mcp_tools.sort(key=self._schema_name)
+        return builtins + mcp_tools
 
     def prepare_call(
         self,
diff --git a/nanobot/providers/anthropic_provider.py b/nanobot/providers/anthropic_provider.py
index 00a7f8271..1cade5fb5 100644
--- a/nanobot/providers/anthropic_provider.py
+++ b/nanobot/providers/anthropic_provider.py
@@ -11,7 +11,6 @@ from collections.abc import Awaitable, Callable
 from typing import Any
 
 import json_repair
-from loguru import logger
 
 from nanobot.providers.base import LLMProvider, LLMResponse, ToolCallRequest
 
@@ -255,8 +254,9 @@ class AnthropicProvider(LLMProvider):
     # Prompt caching
     # ------------------------------------------------------------------
 
-    @staticmethod
+    @classmethod
     def _apply_cache_control(
+        cls,
         system: str | list[dict[str, Any]],
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None,
@@ -283,7 +283,8 @@ class AnthropicProvider(LLMProvider):
         new_tools = tools
         if tools:
             new_tools = list(tools)
-            new_tools[-1] = {**new_tools[-1], "cache_control": marker}
+            for idx in cls._tool_cache_marker_indices(new_tools):
+                new_tools[idx] = {**new_tools[idx], "cache_control": marker}
 
         return system, new_msgs, new_tools
 
diff --git a/nanobot/providers/base.py b/nanobot/providers/base.py
index 5644d194f..118eb80ca 100644
--- a/nanobot/providers/base.py
+++ b/nanobot/providers/base.py
@@ -54,7 +54,7 @@ class LLMResponse:
     retry_after: float | None = None  # Provider supplied retry wait in seconds.
     reasoning_content: str | None = None  # Kimi, DeepSeek-R1, MiMo etc.
     thinking_blocks: list[dict] | None = None  # Anthropic extended thinking
-    
+
     @property
     def has_tool_calls(self) -> bool:
         """Check if response contains tool calls."""
@@ -148,6 +148,38 @@ class LLMProvider(ABC):
             result.append(msg)
         return result
 
+    @staticmethod
+    def _tool_name(tool: dict[str, Any]) -> str:
+        """Extract tool name from either OpenAI or Anthropic-style tool schemas."""
+        name = tool.get("name")
+        if isinstance(name, str):
+            return name
+        fn = tool.get("function")
+        if isinstance(fn, dict):
+            fname = fn.get("name")
+            if isinstance(fname, str):
+                return fname
+        return ""
+
+    @classmethod
+    def _tool_cache_marker_indices(cls, tools: list[dict[str, Any]]) -> list[int]:
+        """Return cache marker indices: builtin/MCP boundary and tail index."""
+        if not tools:
+            return []
+
+        tail_idx = len(tools) - 1
+        last_builtin_idx: int | None = None
+        for i in range(tail_idx, -1, -1):
+            if not cls._tool_name(tools[i]).startswith("mcp_"):
+                last_builtin_idx = i
+                break
+
+        ordered_unique: list[int] = []
+        for idx in (last_builtin_idx, tail_idx):
+            if idx is not None and idx not in ordered_unique:
+                ordered_unique.append(idx)
+        return ordered_unique
+
     @staticmethod
     def _sanitize_request_messages(
         messages: list[dict[str, Any]],
@@ -175,7 +207,7 @@ class LLMProvider(ABC):
     ) -> LLMResponse:
         """
         Send a chat completion request.
-        
+
         Args:
             messages: List of message dicts with 'role' and 'content'.
             tools: Optional list of tool definitions.
@@ -183,7 +215,7 @@ class LLMProvider(ABC):
             max_tokens: Maximum tokens in response.
             temperature: Sampling temperature.
             tool_choice: Tool selection strategy ("auto", "required", or specific tool dict).
-        
+
         Returns:
             LLMResponse with content and/or tool calls.
         """
diff --git a/nanobot/providers/openai_compat_provider.py b/nanobot/providers/openai_compat_provider.py
index 1dca0248b..c9f797705 100644
--- a/nanobot/providers/openai_compat_provider.py
+++ b/nanobot/providers/openai_compat_provider.py
@@ -153,8 +153,9 @@ class OpenAICompatProvider(LLMProvider):
             resolved = env_val.replace("{api_key}", api_key).replace("{api_base}", effective_base)
             os.environ.setdefault(env_name, resolved)
 
-    @staticmethod
+    @classmethod
     def _apply_cache_control(
+        cls,
         messages: list[dict[str, Any]],
         tools: list[dict[str, Any]] | None,
     ) -> tuple[list[dict[str, Any]], list[dict[str, Any]] | None]:
@@ -182,7 +183,8 @@ class OpenAICompatProvider(LLMProvider):
         new_tools = tools
         if tools:
             new_tools = list(tools)
-            new_tools[-1] = {**new_tools[-1], "cache_control": cache_marker}
+            for idx in cls._tool_cache_marker_indices(new_tools):
+                new_tools[idx] = {**new_tools[idx], "cache_control": cache_marker}
         return new_messages, new_tools
 
     @staticmethod
diff --git a/tests/providers/test_prompt_cache_markers.py b/tests/providers/test_prompt_cache_markers.py
new file mode 100644
index 000000000..61d5677de
--- /dev/null
+++ b/tests/providers/test_prompt_cache_markers.py
@@ -0,0 +1,87 @@
+from __future__ import annotations
+
+from typing import Any
+
+from nanobot.providers.anthropic_provider import AnthropicProvider
+from nanobot.providers.openai_compat_provider import OpenAICompatProvider
+
+
+def _openai_tools(*names: str) -> list[dict[str, Any]]:
+    return [
+        {
+            "type": "function",
+            "function": {
+                "name": name,
+                "description": f"{name} tool",
+                "parameters": {"type": "object", "properties": {}},
+            },
+        }
+        for name in names
+    ]
+
+
+def _anthropic_tools(*names: str) -> list[dict[str, Any]]:
+    return [
+        {
+            "name": name,
+            "description": f"{name} tool",
+            "input_schema": {"type": "object", "properties": {}},
+        }
+        for name in names
+    ]
+
+
+def _marked_openai_tool_names(tools: list[dict[str, Any]] | None) -> list[str]:
+    if not tools:
+        return []
+    marked: list[str] = []
+    for tool in tools:
+        if "cache_control" in tool:
+            marked.append((tool.get("function") or {}).get("name", ""))
+    return marked
+
+
+def _marked_anthropic_tool_names(tools: list[dict[str, Any]] | None) -> list[str]:
+    if not tools:
+        return []
+    return [tool.get("name", "") for tool in tools if "cache_control" in tool]
+
+
+def test_openai_compat_marks_builtin_boundary_and_tail_tool() -> None:
+    messages = [
+        {"role": "system", "content": "system"},
+        {"role": "assistant", "content": "assistant"},
+        {"role": "user", "content": "user"},
+    ]
+    _, marked_tools = OpenAICompatProvider._apply_cache_control(
+        messages,
+        _openai_tools("read_file", "write_file", "mcp_fs_ls", "mcp_git_status"),
+    )
+    assert _marked_openai_tool_names(marked_tools) == ["write_file", "mcp_git_status"]
+
+
+def test_anthropic_marks_builtin_boundary_and_tail_tool() -> None:
+    messages = [
+        {"role": "user", "content": "u1"},
+        {"role": "assistant", "content": "a1"},
+        {"role": "user", "content": "u2"},
+    ]
+    _, _, marked_tools = AnthropicProvider._apply_cache_control(
+        "system",
+        messages,
+        _anthropic_tools("read_file", "write_file", "mcp_fs_ls", "mcp_git_status"),
+    )
+    assert _marked_anthropic_tool_names(marked_tools) == ["write_file", "mcp_git_status"]
+
+
+def test_openai_compat_marks_only_tail_without_mcp() -> None:
+    messages = [
+        {"role": "system", "content": "system"},
+        {"role": "assistant", "content": "assistant"},
+        {"role": "user", "content": "user"},
+    ]
+    _, marked_tools = OpenAICompatProvider._apply_cache_control(
+        messages,
+        _openai_tools("read_file", "write_file"),
+    )
+    assert _marked_openai_tool_names(marked_tools) == ["write_file"]
diff --git a/tests/tools/test_tool_registry.py b/tests/tools/test_tool_registry.py
new file mode 100644
index 000000000..5b259119e
--- /dev/null
+++ b/tests/tools/test_tool_registry.py
@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+from typing import Any
+
+from nanobot.agent.tools.base import Tool
+from nanobot.agent.tools.registry import ToolRegistry
+
+
+class _FakeTool(Tool):
+    def __init__(self, name: str):
+        self._name = name
+
+    @property
+    def name(self) -> str:
+        return self._name
+
+    @property
+    def description(self) -> str:
+        return f"{self._name} tool"
+
+    @property
+    def parameters(self) -> dict[str, Any]:
+        return {"type": "object", "properties": {}}
+
+    async def execute(self, **kwargs: Any) -> Any:
+        return kwargs
+
+
+def _tool_names(definitions: list[dict[str, Any]]) -> list[str]:
+    names: list[str] = []
+    for definition in definitions:
+        fn = definition.get("function", {})
+        names.append(fn.get("name", ""))
+    return names
+
+
+def test_get_definitions_orders_builtins_then_mcp_tools() -> None:
+    registry = ToolRegistry()
+    registry.register(_FakeTool("mcp_git_status"))
+    registry.register(_FakeTool("write_file"))
+    registry.register(_FakeTool("mcp_fs_list"))
+    registry.register(_FakeTool("read_file"))
+
+    assert _tool_names(registry.get_definitions()) == [
+        "read_file",
+        "write_file",
+        "mcp_fs_list",
+        "mcp_git_status",
+    ]