feat: Make skill instruction optimizable and can adapt to user tasks

PiperOrigin-RevId: 869971535

contributing/samples/skills_agent/agent.py

@@ -19,6 +19,7 @@ import pathlib
 from google.adk import Agent
 from google.adk.skills import load_skill_from_dir
 from google.adk.skills import models
+from google.adk.skills.prompt import DEFAULT_SKILL_SYSTEM_INSTRUCTION
 from google.adk.tools import skill_toolset
 
 greeting_skill = models.Skill(
@@ -52,9 +53,7 @@ root_agent = Agent(
     model="gemini-2.5-flash",
     name="skill_user_agent",
     description="An agent that can use specialized skills.",
-    instruction=(
-        "You are a helpful assistant that can leverage skills to perform tasks."
-    ),
+    instruction=DEFAULT_SKILL_SYSTEM_INSTRUCTION,
     tools=[
         my_skill_toolset,
     ],

src/google/adk/skills/__init__.py

@@ -18,6 +18,7 @@ from .models import Frontmatter
 from .models import Resources
 from .models import Script
 from .models import Skill
+from .prompt import DEFAULT_SKILL_SYSTEM_INSTRUCTION
 from .utils import load_skill_from_dir
 
 __all__ = [
@@ -25,5 +26,6 @@ __all__ = [
     "Resources",
     "Script",
     "Skill",
+    "DEFAULT_SKILL_SYSTEM_INSTRUCTION",
     "load_skill_from_dir",
 ]

src/google/adk/skills/prompt.py

@@ -21,6 +21,21 @@ from typing import List
 
 from . import models
 
+DEFAULT_SKILL_SYSTEM_INSTRUCTION = """You can use specialized 'skills' to help you with complex tasks. You MUST use the skill tools to interact with these skills.
+
+Skills are folders of instructions and resources that extend your capabilities for specialized tasks. Each skill folder contains:
+- **SKILL.md** (required): The main instruction file with skill metadata and detailed markdown instructions.
+- **references/** (Optional): Additional documentation or examples for skill usage.
+- **assets/** (Optional): Templates, scripts or other resources used by the skill.
+
+This is very important:
+
+1. Use the `list_skills` tool to discover available skills.
+2. If a skill seems relevant to the current user query, you MUST use the `load_skill` tool with `name="<SKILL_NAME>"` to read its full instructions before proceeding.
+3. Once you have read the instructions, follow them exactly as documented before replying to the user. For example, If the instruction lists multiple steps, please make sure you complete all of them in order.
+4. The `load_skill_resource` tool is for viewing files within a skill's directory (e.g., `references/*`, `assets/*`). Do NOT use other tools to access these files.
+"""
+
 
 def format_skills_as_xml(skills: List[models.Frontmatter]) -> str:
   """Formats available skills into a standard XML string.

src/google/adk/tools/skill_toolset.py

@@ -23,7 +23,6 @@ from google.genai import types
 from ..agents.readonly_context import ReadonlyContext
 from ..features import experimental
 from ..features import FeatureName
-from ..models.llm_request import LlmRequest
 from ..skills import models
 from ..skills import prompt
 from .base_tool import BaseTool
@@ -31,6 +30,36 @@ from .base_toolset import BaseToolset
 from .tool_context import ToolContext
 
 
+@experimental(FeatureName.SKILL_TOOLSET)
+class ListSkillsTool(BaseTool):
+  """Tool to list all available skills."""
+
+  def __init__(self, toolset: "SkillToolset"):
+    super().__init__(
+        name="list_skills",
+        description=(
+            "Lists all available skills with their names and descriptions."
+        ),
+    )
+    self._toolset = toolset
+
+  def _get_declaration(self) -> types.FunctionDeclaration | None:
+    return types.FunctionDeclaration(
+        name=self.name,
+        description=self.description,
+        parameters_json_schema={
+            "type": "object",
+            "properties": {},
+        },
+    )
+
+  async def run_async(
+      self, *, args: dict[str, Any], tool_context: ToolContext
+  ) -> Any:
+    skill_frontmatters = self._toolset._list_skills()
+    return prompt.format_skills_as_xml(skill_frontmatters)
+
+
 @experimental(FeatureName.SKILL_TOOLSET)
 class LoadSkillTool(BaseTool):
   """Tool to load a skill's instructions."""
@@ -179,6 +208,7 @@ class SkillToolset(BaseToolset):
     super().__init__()
     self._skills = {skill.name: skill for skill in skills}
     self._tools = [
+        ListSkillsTool(self),
         LoadSkillTool(self),
         LoadSkillResourceTool(self),
     ]
@@ -196,33 +226,3 @@ class SkillToolset(BaseToolset):
   def _list_skills(self) -> list[models.Frontmatter]:
     """Lists the frontmatter of all available skills."""
     return [s.frontmatter for s in self._skills.values()]
-
-  async def process_llm_request(
-      self,
-      *,
-      tool_context: ToolContext,
-      llm_request: LlmRequest,
-  ) -> None:
-    """Adds available skills to the system instruction."""
-
-    skill_frontmatters = self._list_skills()
-
-    # Append the skill instruction into the system instruction
-    skills_xml = prompt.format_skills_as_xml(skill_frontmatters)
-    skill_si = f"""
-You can use specialized 'skills' to help you with complex tasks. Each skill has a name and a description listed below:
-{skills_xml}
-
-Skills are folders of instructions and resources that extend your capabilities for specialized tasks. Each skill folder contains:
-- **SKILL.md** (required): The main instruction file with skill metadata and detailed markdown instructions.
-- **references/** (Optional): Additional documentation or examples for skill usage.
-- **assets/** (Optional): Templates, scripts or other resources used by the skill.
-
-This is very important:
-
-1. If a skill seems relevant to the current user query, you MUST use the `load_skill` tool with `name="<SKILL_NAME>"` to read its full instructions before proceeding.
-2. Once you have read the instructions, follow them exactly as documented before replying to the user. For example, If the instruction lists multiple steps, please make sure you complete all of them in order.
-3. The `load_skill_resource` tool is for viewing files within a skill's directory (e.g., `references/*`, `assets/*`). Do NOT use other tools to access these files.
-"""
-
-    llm_request.append_instructions([skill_si])

tests/unittests/tools/test_skill_toolset.py

@@ -14,7 +14,6 @@
 
 from unittest import mock
 
-from google.adk.models import llm_request
 from google.adk.skills import models
 from google.adk.tools import skill_toolset
 from google.adk.tools import tool_context
@@ -124,32 +123,23 @@ def test_list_skills(mock_skill1, mock_skill2):
 async def test_get_tools(mock_skill1, mock_skill2):
   toolset = skill_toolset.SkillToolset([mock_skill1, mock_skill2])
   tools = await toolset.get_tools()
-  assert len(tools) == 2
-  assert isinstance(tools[0], skill_toolset.LoadSkillTool)
-  assert isinstance(tools[1], skill_toolset.LoadSkillResourceTool)
+  assert len(tools) == 3
+  assert isinstance(tools[0], skill_toolset.ListSkillsTool)
+  assert isinstance(tools[1], skill_toolset.LoadSkillTool)
+  assert isinstance(tools[2], skill_toolset.LoadSkillResourceTool)
 
 
 @pytest.mark.asyncio
-async def test_process_llm_request(
+@pytest.mark.asyncio
+async def test_list_skills_tool(
     mock_skill1, mock_skill2, tool_context_instance
 ):
   toolset = skill_toolset.SkillToolset([mock_skill1, mock_skill2])
-  mock_llm_request = llm_request.LlmRequest()
-  mock_llm_request.config.system_instruction = "existing instruction"
-  await toolset.process_llm_request(
-      tool_context=tool_context_instance, llm_request=mock_llm_request
-  )
-  assert "<available_skills>" in mock_llm_request.config.system_instruction
-  assert (
-      "You can use specialized 'skills'"
-      in mock_llm_request.config.system_instruction
-  )
-  assert (
-      "skills are folders" in mock_llm_request.config.system_instruction.lower()
-  )
-  assert mock_llm_request.config.system_instruction.startswith(
-      "existing instruction"
-  )
+  tool = skill_toolset.ListSkillsTool(toolset)
+  result = await tool.run_async(args={}, tool_context=tool_context_instance)
+  assert "<available_skills>" in result
+  assert "skill1" in result
+  assert "skill2" in result
 
 
 @pytest.mark.asyncio