feat: Add models.py and prompt.py to adk/skills to use in skill toolset

Also redefined schemas in models.py to be pydantic.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 866270203

src/google/adk/skills/__init__.py

@@ -0,0 +1,29 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Agent Development Kit - Skills."""
+
+from .models import Frontmatter
+from .models import Resources
+from .models import Script
+from .models import Skill
+from .prompt import format_skills_as_xml
+
+__all__ = [
+    "Frontmatter",
+    "Resources",
+    "Script",
+    "Skill",
+    "format_skills_as_xml",
+]

src/google/adk/skills/models.py

@@ -0,0 +1,148 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Data models for Agent Skills."""
+
+from __future__ import annotations
+
+from typing import Optional
+
+from pydantic import BaseModel
+
+
+class Frontmatter(BaseModel):
+  """L1 skill content: metadata parsed from SKILL.md frontmatter for skill discovery.
+
+  Attributes:
+      name: Skill name in kebab-case (required).
+      description: What the skill does and when the model should use it
+        (required).
+      license: License for the skill (optional).
+      compatibility: Compatibility information for the skill (optional).
+      allowed_tools: Tool patterns the skill requires (optional, experimental).
+      metadata: Key-value pairs for client-specific properties (defaults to
+        empty dict).
+  """
+
+  name: str
+  description: str
+  license: Optional[str] = None
+  compatibility: Optional[str] = None
+  allowed_tools: Optional[str] = None
+  metadata: dict[str, str] = {}
+
+
+class Script(BaseModel):
+  """Wrapper for script content."""
+
+  src: str
+
+  def __str__(self) -> str:
+    """Returns the string representation of the script content.
+
+    This ensures that any script type can be converted to a string, which is
+    useful for including the script in prompts or saving it to the file system.
+    """
+    return self.src
+
+
+class Resources(BaseModel):
+  """L3 skill content: additional instructions, assets, and scripts, loaded as needed.
+
+  Attributes:
+      references: Additional markdown files with instructions, workflows, or
+        guidance.
+      assets: Resource materials like database schemas, API documentation,
+        templates, or examples.
+      scripts: Executable scripts that can be run via bash.
+  """
+
+  references: dict[str, str] = {}
+  assets: dict[str, str] = {}
+  scripts: dict[str, Script] = {}
+
+  def get_reference(self, reference_id: str) -> Optional[str]:
+    """Get content of a reference file.
+
+    Args:
+        reference_id: Unique path or name of the reference file.
+
+    Returns:
+        Reference content as string, or None if not found
+    """
+    return self.references.get(reference_id)
+
+  def get_asset(self, asset_id: str) -> Optional[str]:
+    """Get content of an asset file.
+
+    Args:
+        asset_id: Unique path or name of the asset file.
+
+    Returns:
+        Asset content as string, or None if not found
+    """
+    return self.assets.get(asset_id)
+
+  def get_script(self, script_id: str) -> Optional[Script]:
+    """Get content of a script file.
+
+    Args:
+        script_id: Unique path or name of the script file.
+
+    Returns:
+        Script object, or None if not found
+    """
+    return self.scripts.get(script_id)
+
+  def list_references(self) -> list[str]:
+    """List all available reference paths."""
+    return list(self.references.keys())
+
+  def list_assets(self) -> list[str]:
+    """List all available asset paths."""
+    return list(self.assets.keys())
+
+  def list_scripts(self) -> list[str]:
+    """List all available script paths."""
+    return list(self.scripts.keys())
+
+
+class Skill(BaseModel):
+  """Complete skill representation including frontmatter, instructions, and resources.
+
+  A skill combines:
+  - L1: Frontmatter for discovery (name, description).
+  - L2: Instructions from SKILL.md body, loaded when skill is triggered.
+  - L3: Resources including additional instructions, assets, and scripts,
+  loaded as needed.
+
+  Attributes:
+      frontmatter: Parsed skill frontmatter from SKILL.md.
+      instructions: L2 skill content: markdown instruction from SKILL.md body.
+      resources: L3 skill content: additional instructions, assets, and scripts.
+  """
+
+  frontmatter: Frontmatter
+  instructions: str
+  resources: Resources = Resources()
+
+  @property
+  def name(self) -> str:
+    """Convenience property to access skill name."""
+    return self.frontmatter.name
+
+  @property
+  def description(self) -> str:
+    """Convenience property to access skill description."""
+    return self.frontmatter.description

src/google/adk/skills/prompt.py

@@ -0,0 +1,53 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module for skill prompt generation."""
+
+from __future__ import annotations
+
+import html
+from typing import List
+
+from . import models
+
+
+def format_skills_as_xml(skills: List[models.Frontmatter]) -> str:
+  """Formats available skills into a standard XML string.
+
+  Args:
+    skills: A list of skill frontmatter objects.
+
+  Returns:
+      XML string with <available_skills> block containing each skill's
+      name and description.
+  """
+
+  if not skills:
+    return "<available_skills>\n</available_skills>"
+
+  lines = ["<available_skills>"]
+
+  for skill in skills:
+    lines.append("<skill>")
+    lines.append("<name>")
+    lines.append(html.escape(skill.name))
+    lines.append("</name>")
+    lines.append("<description>")
+    lines.append(html.escape(skill.description))
+    lines.append("</description>")
+    lines.append("</skill>")
+
+  lines.append("</available_skills>")
+
+  return "\n".join(lines)

tests/unittests/skills/__init__.py

@@ -0,0 +1,13 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.

tests/unittests/skills/test_models.py

@@ -0,0 +1,70 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unit tests for skill models."""
+
+from google.adk.skills import models
+import pytest
+
+
+def test_frontmatter():
+  """Tests Frontmatter model."""
+  frontmatter = models.Frontmatter(
+      name="test-skill",
+      description="Test description",
+      license="Apache 2.0",
+      compatibility="test",
+      allowed_tools="test",
+      metadata={"key": "value"},
+  )
+  assert frontmatter.name == "test-skill"
+  assert frontmatter.description == "Test description"
+  assert frontmatter.license == "Apache 2.0"
+  assert frontmatter.compatibility == "test"
+  assert frontmatter.allowed_tools == "test"
+  assert frontmatter.metadata == {"key": "value"}
+
+
+def test_resources():
+  """Tests Resources model."""
+  resources = models.Resources(
+      references={"ref1": "ref content"},
+      assets={"asset1": "asset content"},
+      scripts={"script1": models.Script(src="print('hello')")},
+  )
+  assert resources.get_reference("ref1") == "ref content"
+  assert resources.get_asset("asset1") == "asset content"
+  assert resources.get_script("script1").src == "print('hello')"
+  assert resources.get_reference("ref2") is None
+  assert resources.get_asset("asset2") is None
+  assert resources.get_script("script2") is None
+  assert resources.list_references() == ["ref1"]
+  assert resources.list_assets() == ["asset1"]
+  assert resources.list_scripts() == ["script1"]
+
+
+def test_skill_properties():
+  """Tests Skill model."""
+  frontmatter = models.Frontmatter(
+      name="my-skill", description="my description"
+  )
+  skill = models.Skill(frontmatter=frontmatter, instructions="do this")
+  assert skill.name == "my-skill"
+  assert skill.description == "my description"
+
+
+def test_script_to_string():
+  """Tests Script model."""
+  script = models.Script(src="print('hello')")
+  assert str(script) == "print('hello')"

tests/unittests/skills/test_prompt.py

@@ -0,0 +1,49 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unit tests for prompt."""
+
+from google.adk.skills import models
+from google.adk.skills import prompt
+import pytest
+
+
+class TestPrompt:
+
+  def test_format_skills_as_xml(self):
+    skills = [
+        models.Frontmatter(name="skill1", description="desc1"),
+        models.Frontmatter(name="skill2", description="desc2"),
+    ]
+    xml = prompt.format_skills_as_xml(skills)
+
+    assert "<name>\nskill1\n</name>" in xml
+    assert "<description>\ndesc1\n</description>" in xml
+    assert "<location>" not in xml
+    assert "<name>\nskill2\n</name>" in xml
+    assert "<description>\ndesc2\n</description>" in xml
+    assert xml.startswith("<available_skills>")
+    assert xml.endswith("</available_skills>")
+
+  def test_format_skills_as_xml_empty(self):
+    xml = prompt.format_skills_as_xml([])
+    assert xml == "<available_skills>\n</available_skills>"
+
+  def test_format_skills_as_xml_escaping(self):
+    skills = [
+        models.Frontmatter(name="skill&name", description="desc<ription>"),
+    ]
+    xml = prompt.format_skills_as_xml(skills)
+    assert "skill&amp;name" in xml
+    assert "desc&lt;ription&gt;" in xml