diff --git a/chatlas/_content.py b/chatlas/_content.py
index b8b17b65..2243343e 100644
--- a/chatlas/_content.py
+++ b/chatlas/_content.py
@@ -18,6 +18,8 @@
 from ._typing_extensions import TypedDict
 
 if TYPE_CHECKING:
+    from htmltools import Tagified
+
     from ._tools import Tool, ToolBuiltIn
 
 
@@ -316,7 +318,7 @@ def _format_arg(value: object) -> str:
     def _repr_html_(self) -> str:
         return str(self.tagify())
 
-    def tagify(self):
+    def tagify(self) -> Tagified:
         "Returns an HTML string suitable for passing to htmltools/shiny's `Chat()` component."
         try:
             from htmltools import HTML, TagList, head_content, tags
@@ -331,7 +333,7 @@ def tagify(self):
         return TagList(
             HTML(html),
             head_content(tags.style(TOOL_CSS)),
-        )
+        ).tagify()
 
 
 class ContentToolResult(Content):
@@ -523,7 +525,7 @@ def _to_json(value: Any) -> object:
     def _repr_html_(self):
         return str(self.tagify())
 
-    def tagify(self):
+    def tagify(self) -> Tagified:
         "A method for rendering this object via htmltools/shiny."
         try:
             from htmltools import HTML, html_escape
@@ -694,7 +696,7 @@ def __str__(self):
     def _repr_html_(self):
         return str(self.tagify())
 
-    def tagify(self):
+    def tagify(self) -> Tagified:
         try:
             from htmltools import HTML
         except ImportError:
diff --git a/pyproject.toml b/pyproject.toml
index 9b9ab8d7..004c536e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,7 +50,7 @@ dev = [
     "matplotlib",
     "Pillow",
     "shiny",
-    "htmltools",
+    "htmltools>=0.7.0;python_version>='3.10'",
     "shinychat",
     "narwhals",
     "pandas",
@@ -208,3 +208,11 @@ skip-magic-trailing-comma = false
 line-ending = "auto"
 docstring-code-format = true
 docstring-code-line-length = "dynamic"
+
+
+# TODO(htmltools-105): remove this source override before merging.
+# Pins htmltools to the PR branch that adds the `Tagified` alias
+# (posit-dev/py-htmltools#106). Flip back to the released htmltools
+# once it ships.
+[tool.uv.sources]
+htmltools = { git = "https://github.com/posit-dev/py-htmltools.git", branch = "main" }