docs: add mypy plugin configuration note for param (#8614)

doc/how_to/index.md

@@ -21,6 +21,13 @@ How to effectively develop apps in a notebook environment.
 How to effectively develop apps in a Python or Markdown file.
 :::
 
+:::{grid-item-card} {octicon}`file-code;2.5em;sd-mr-1 sd-animate-grow50` Type check your code
+:link: typing/index
+:link-type: doc
+
+How to configure static type checkers like mypy to work with Param and Panel.
+:::
+
 ::::
 
 ## Build apps

doc/how_to/prepare_to_develop.md

@@ -12,4 +12,5 @@
 
 Develop in a notebook<notebook/index>
 Develop in an editor<editor/index>
+Type check your code<typing/index>
 ```

doc/how_to/typing/index.md

@@ -0,0 +1,54 @@
+# Type Checking with Param and Panel
+
+This guide covers how to configure static type checkers (like mypy) when working with Panel and Param.
+
+## Why this matters
+
+Panel is built on top of [Param](https://param.holoviz.org), which uses a custom metaclass to route class-level parameter assignment through Python's descriptor protocol. Static type checkers like mypy don't understand this pattern out of the box, and will reject valid code such as:
+
+```python
+import panel as pn
+
+pn.chat.ChatMessage.show_reaction_icons = False
+```
+
+Running mypy on this without the plugin produces an error:
+
+```console
+$ mypy script.py
+script.py:3: error: Incompatible types in assignment (expression has type "bool", variable has type "Boolean[bool]")  [assignment]
+Found 1 error in 1 file (checked 1 source file)
+```
+
+This is a real issue for projects that run mypy in CI/CD, since it can block releases or force you to spend time silencing false-positive errors.
+
+To fix this, Param ships a dedicated mypy plugin.
+
+## Enabling the Param mypy plugin
+
+Add the following to your `pyproject.toml`:
+
+```toml
+[tool.mypy]
+plugins = ["param.mypy_plugin"]
+```
+
+Or, if you're using `mypy.ini` / `setup.cfg`:
+
+```ini
+[mypy]
+plugins = param.mypy_plugin
+```
+
+With the plugin enabled, mypy correctly understands that assignments like `pn.chat.ChatMessage.show_reaction_icons = False` set the parameter's default value, and type-checks them accordingly — no more false-positive errors in CI.
+
+## Learn more
+
+Param's user guide has a full [Typing guide](https://param.holoviz.org/en/latest/user_guide/Typing.html) covering:
+
+- Type inference from Parameter types
+- Choice of type checker (mypy, basedpyright)
+- Known limitations
+- Practical recommendations
+
+If you're setting up type checking for a Panel project, that guide is the best place to go for details beyond the mypy plugin itself.