diff --git a/src/personal_mcp/registry/models/common.py b/src/personal_mcp/registry/models/common.py
index ec1c434..242cf2c 100644
--- a/src/personal_mcp/registry/models/common.py
+++ b/src/personal_mcp/registry/models/common.py
@@ -14,6 +14,8 @@ SEMVER_RE: Final[re.Pattern[str]] = re.compile(r"^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0
 
 
 class StrictFrozenModel(BaseModel):
+    """Immutable base model with strict field validation rules."""
+
     model_config: ClassVar[ConfigDict] = ConfigDict(
         extra="forbid",
         frozen=True,
@@ -28,6 +30,8 @@ def frozen_mapping[K, V](value: Mapping[K, V] | None = None) -> Mapping[K, V]:
 
 
 class ReferenceEntry(StrictFrozenModel):
+    """Reference metadata for a markdown file within a skill."""
+
     path: str
     mime_type: str = "text/markdown"
     title: str | None = None
diff --git a/src/personal_mcp/registry/models/document.py b/src/personal_mcp/registry/models/document.py
index ebd7234..cb94dc6 100644
--- a/src/personal_mcp/registry/models/document.py
+++ b/src/personal_mcp/registry/models/document.py
@@ -5,6 +5,8 @@ from .common import StrictFrozenModel
 
 
 class MarkdownDocumentModel(StrictFrozenModel):
+    """Normalized markdown document content with path and frontmatter."""
+
     relpath: str
     content: str
     frontmatter: str | None = None
@@ -12,6 +14,8 @@ class MarkdownDocumentModel(StrictFrozenModel):
 
 
 class SkillFilesBundleModel(StrictFrozenModel):
+    """Grouped skill documents partitioned into skill, references, and other files."""
+
     slug: str
     skill: MarkdownDocumentModel
     references: tuple[MarkdownDocumentModel, ...] = ()
diff --git a/src/personal_mcp/registry/models/prompt.py b/src/personal_mcp/registry/models/prompt.py
index 6376f21..1003ce9 100644
--- a/src/personal_mcp/registry/models/prompt.py
+++ b/src/personal_mcp/registry/models/prompt.py
@@ -22,6 +22,8 @@ type PromptArgumentType = Literal[
 
 
 class PromptArgumentEntry(StrictFrozenModel):
+    """Schema for a single prompt argument definition."""
+
     type: PromptArgumentType
     description: str | None = None
     required: bool = False
@@ -37,6 +39,8 @@ class PromptArgumentEntry(StrictFrozenModel):
 
 
 class PromptMetadata(StrictFrozenModel):
+    """Canonical metadata describing a prompt contract and arguments."""
+
     id: str
     version: str
     tags: tuple[str, ...] = ()
@@ -80,6 +84,8 @@ class PromptMetadata(StrictFrozenModel):
 
 
 class PromptFrontmatter(StrictFrozenModel):
+    """Parsed PROMPT frontmatter including personal-mcp metadata."""
+
     name: str = Field(min_length=1, max_length=64)
     description: str = Field(min_length=1, max_length=1024)
     x_personal_mcp: PromptMetadata = Field(alias="x-personal-mcp")
@@ -95,6 +101,8 @@ class PromptFrontmatter(StrictFrozenModel):
 
 
 class PromptDocumentModel(StrictFrozenModel):
+    """Structured representation of a prompt markdown document."""
+
     prompt_id: str
     relpath: str
     content: str
diff --git a/src/personal_mcp/registry/models/registry.py b/src/personal_mcp/registry/models/registry.py
index 17d1602..83cff48 100644
--- a/src/personal_mcp/registry/models/registry.py
+++ b/src/personal_mcp/registry/models/registry.py
@@ -9,6 +9,8 @@ from .prompt import PromptArgumentEntry
 
 
 class ReferenceRecord(StrictFrozenModel):
+    """Registry record for a resolved skill reference document."""
+
     ref_id: str
     uri: str
     relpath: str
@@ -18,6 +20,8 @@ class ReferenceRecord(StrictFrozenModel):
 
 
 class SkillRecord(StrictFrozenModel):
+    """Registry record containing a fully resolved skill and references."""
+
     skill_id: str
     name: str
     description: str
@@ -37,6 +41,8 @@ class SkillRecord(StrictFrozenModel):
 
 
 class SkillSummaryRecord(StrictFrozenModel):
+    """Compact skill summary exposed by catalog listing APIs."""
+
     skill_id: str
     name: str
     description: str
@@ -47,6 +53,8 @@ class SkillSummaryRecord(StrictFrozenModel):
 
 
 class PromptRecord(StrictFrozenModel):
+    """Registry record containing a fully resolved prompt document."""
+
     prompt_id: str
     name: str
     description: str
@@ -65,6 +73,8 @@ class PromptRecord(StrictFrozenModel):
 
 
 class PromptSummaryRecord(StrictFrozenModel):
+    """Compact prompt summary exposed by catalog listing APIs."""
+
     prompt_id: str
     name: str
     description: str
@@ -75,6 +85,8 @@ class PromptSummaryRecord(StrictFrozenModel):
 
 
 class DocsRegistry(StrictFrozenModel):
+    """In-memory index of loaded skills, prompts, and docs content."""
+
     skills_by_id: Mapping[str, SkillRecord] = Field(default_factory=frozen_mapping)
     skills_in_load_order: tuple[str, ...]
     skills_summary_in_load_order: tuple[SkillSummaryRecord, ...]
diff --git a/src/personal_mcp/registry/models/skill.py b/src/personal_mcp/registry/models/skill.py
index a83205b..ec143ea 100644
--- a/src/personal_mcp/registry/models/skill.py
+++ b/src/personal_mcp/registry/models/skill.py
@@ -1,4 +1,5 @@
 from collections.abc import Mapping
+from pathlib import PurePosixPath
 
 from pydantic import Field
 from pydantic import field_validator
@@ -13,6 +14,8 @@ type ToolSelector = str | tuple[str, ...]
 
 
 class SkillMetadata(StrictFrozenModel):
+    """Canonical metadata describing a skill and its dependencies."""
+
     id: str
     version: str
     tags: tuple[str, ...] = ()
@@ -65,6 +68,8 @@ class SkillMetadata(StrictFrozenModel):
 
 
 class SkillFrontmatter(StrictFrozenModel):
+    """Parsed SKILL frontmatter including standard and personal-mcp fields."""
+
     name: str = Field(min_length=1, max_length=64)
     description: str = Field(min_length=1, max_length=1024)
     when_to_use: str | None = None
@@ -103,14 +108,18 @@ class SkillFrontmatter(StrictFrozenModel):
 
 
 class SkillDocumentModel(StrictFrozenModel):
+    """Structured representation of a skill markdown document."""
+
     skill_id: str
-    relpath: str
+    relpath: PurePosixPath
     content: str
     frontmatter: SkillFrontmatter
 
 
 class SkillReferenceDocumentModel(StrictFrozenModel):
+    """Structured representation of a skill reference markdown document."""
+
     ref_id: str
-    relpath: str
+    relpath: PurePosixPath
     content: str
     entry: ReferenceEntry