diff --git a/crates/ty/docs/rules.md b/crates/ty/docs/rules.md
index b36ccae657..9ca4ce01da 100644
--- a/crates/ty/docs/rules.md
+++ b/crates/ty/docs/rules.md
@@ -52,7 +52,7 @@ Calling a non-callable object will raise a `TypeError` at runtime.
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20call-non-callable)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L94)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L95)
 </details>
 
 ## `conflicting-argument-forms`
@@ -83,7 +83,7 @@ f(int)  # error
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20conflicting-argument-forms)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L138)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L139)
 </details>
 
 ## `conflicting-declarations`
@@ -113,7 +113,7 @@ a = 1
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20conflicting-declarations)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L164)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L165)
 </details>
 
 ## `conflicting-metaclass`
@@ -144,7 +144,7 @@ class C(A, B): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20conflicting-metaclass)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L189)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L190)
 </details>
 
 ## `cyclic-class-definition`
@@ -175,7 +175,7 @@ class B(A): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20cyclic-class-definition)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L215)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L216)
 </details>
 
 ## `duplicate-base`
@@ -201,7 +201,44 @@ class B(A, A): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20duplicate-base)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L259)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L260)
+</details>
+
+## `duplicate-kw-only`
+
+**Default level**: error
+
+<details>
+<summary>detects dataclass definitions with more than once usages of <code>KW_ONLY</code></summary>
+
+### What it does
+Checks for dataclass definitions with more than one field
+annotated with `KW_ONLY`.
+
+### Why is this bad?
+`dataclasses.KW_ONLY` is a special marker used to
+emulate the `*` syntax in normal signatures.
+It can only be used once per dataclass.
+
+Attempting to annotate two different fields with
+it will lead to a runtime error.
+
+### Examples
+```python
+from dataclasses import dataclass, KW_ONLY
+
+@dataclass
+class A:  # Crash at runtime
+    b: int
+    _1: KW_ONLY
+    c: str
+    _2: KW_ONLY
+    d: bytes
+```
+
+### Links
+* [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20duplicate-kw-only)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L281)
 </details>
 
 ## `escape-character-in-forward-annotation`
@@ -338,7 +375,7 @@ TypeError: multiple bases have instance lay-out conflict
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20incompatible-slots)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L280)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L313)
 </details>
 
 ## `inconsistent-mro`
@@ -367,7 +404,7 @@ class C(A, B): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20inconsistent-mro)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L366)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L399)
 </details>
 
 ## `index-out-of-bounds`
@@ -392,7 +429,7 @@ t[3]  # IndexError: tuple index out of range
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20index-out-of-bounds)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L390)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L423)
 </details>
 
 ## `invalid-argument-type`
@@ -418,7 +455,7 @@ func("foo")  # error: [invalid-argument-type]
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-argument-type)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L410)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L443)
 </details>
 
 ## `invalid-assignment`
@@ -445,7 +482,7 @@ a: int = ''
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-assignment)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L450)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L483)
 </details>
 
 ## `invalid-attribute-access`
@@ -478,7 +515,7 @@ C.instance_var = 3  # error: Cannot assign to instance variable
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-attribute-access)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1454)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1487)
 </details>
 
 ## `invalid-base`
@@ -501,7 +538,7 @@ class A(42): ...  # error: [invalid-base]
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-base)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L472)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L505)
 </details>
 
 ## `invalid-context-manager`
@@ -527,7 +564,7 @@ with 1:
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-context-manager)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L523)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L556)
 </details>
 
 ## `invalid-declaration`
@@ -555,7 +592,7 @@ a: str
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-declaration)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L544)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L577)
 </details>
 
 ## `invalid-exception-caught`
@@ -596,7 +633,7 @@ except ZeroDivisionError:
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-exception-caught)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L567)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L600)
 </details>
 
 ## `invalid-generic-class`
@@ -627,7 +664,7 @@ class C[U](Generic[T]): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-generic-class)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L603)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L636)
 </details>
 
 ## `invalid-legacy-type-variable`
@@ -660,7 +697,7 @@ def f(t: TypeVar("U")): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-legacy-type-variable)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L629)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L662)
 </details>
 
 ## `invalid-metaclass`
@@ -692,7 +729,7 @@ class B(metaclass=f): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-metaclass)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L678)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L711)
 </details>
 
 ## `invalid-overload`
@@ -740,7 +777,7 @@ def foo(x: int) -> int: ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-overload)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L705)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L738)
 </details>
 
 ## `invalid-parameter-default`
@@ -765,7 +802,7 @@ def f(a: int = ''): ...
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-parameter-default)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L748)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L781)
 </details>
 
 ## `invalid-protocol`
@@ -798,7 +835,7 @@ TypeError: Protocols can only inherit from other protocols, got <class 'int'>
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-protocol)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L338)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L371)
 </details>
 
 ## `invalid-raise`
@@ -846,7 +883,7 @@ def g():
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-raise)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L768)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L801)
 </details>
 
 ## `invalid-return-type`
@@ -870,7 +907,7 @@ def func() -> int:
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-return-type)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L431)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L464)
 </details>
 
 ## `invalid-super-argument`
@@ -914,7 +951,7 @@ super(B, A)  # error: `A` does not satisfy `issubclass(A, B)`
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-super-argument)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L811)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L844)
 </details>
 
 ## `invalid-syntax-in-forward-annotation`
@@ -954,7 +991,7 @@ NewAlias = TypeAliasType(get_name(), int)        # error: TypeAliasType name mus
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-alias-type)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L657)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L690)
 </details>
 
 ## `invalid-type-checking-constant`
@@ -983,7 +1020,7 @@ TYPE_CHECKING = ''
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-checking-constant)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L850)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L883)
 </details>
 
 ## `invalid-type-form`
@@ -1012,7 +1049,7 @@ b: Annotated[int]  # `Annotated` expects at least two arguments
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-form)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L874)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L907)
 </details>
 
 ## `invalid-type-guard-call`
@@ -1045,7 +1082,7 @@ f(10)  # Error
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-guard-call)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L926)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L959)
 </details>
 
 ## `invalid-type-guard-definition`
@@ -1078,7 +1115,7 @@ class C:
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-guard-definition)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L898)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L931)
 </details>
 
 ## `invalid-type-variable-constraints`
@@ -1112,7 +1149,7 @@ T = TypeVar('T', bound=str)  # valid bound TypeVar
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-variable-constraints)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L954)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L987)
 </details>
 
 ## `missing-argument`
@@ -1136,7 +1173,7 @@ func()  # TypeError: func() missing 1 required positional argument: 'x'
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20missing-argument)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L983)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1016)
 </details>
 
 ## `no-matching-overload`
@@ -1164,7 +1201,7 @@ func("string")  # error: [no-matching-overload]
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20no-matching-overload)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1002)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1035)
 </details>
 
 ## `non-subscriptable`
@@ -1187,7 +1224,7 @@ Subscripting an object that does not support it will raise a `TypeError` at runt
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20non-subscriptable)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1025)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1058)
 </details>
 
 ## `not-iterable`
@@ -1212,7 +1249,7 @@ for i in 34:  # TypeError: 'int' object is not iterable
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20not-iterable)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1043)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1076)
 </details>
 
 ## `parameter-already-assigned`
@@ -1238,7 +1275,7 @@ f(1, x=2)  # Error raised here
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20parameter-already-assigned)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1094)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1127)
 </details>
 
 ## `raw-string-type-annotation`
@@ -1297,7 +1334,7 @@ static_assert(int(2.0 * 3.0) == 6)  # error: does not have a statically known tr
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20static-assert-error)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1430)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1463)
 </details>
 
 ## `subclass-of-final-class`
@@ -1325,7 +1362,7 @@ class B(A): ...  # Error raised here
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20subclass-of-final-class)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1185)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1218)
 </details>
 
 ## `too-many-positional-arguments`
@@ -1351,7 +1388,7 @@ f("foo")  # Error raised here
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20too-many-positional-arguments)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1230)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1263)
 </details>
 
 ## `type-assertion-failure`
@@ -1378,7 +1415,7 @@ def _(x: int):
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20type-assertion-failure)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1208)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1241)
 </details>
 
 ## `unavailable-implicit-super-arguments`
@@ -1422,7 +1459,7 @@ class A:
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unavailable-implicit-super-arguments)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1251)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1284)
 </details>
 
 ## `unknown-argument`
@@ -1448,7 +1485,7 @@ f(x=1, y=2)  # Error raised here
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unknown-argument)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1308)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1341)
 </details>
 
 ## `unresolved-attribute`
@@ -1475,7 +1512,7 @@ A().foo  # AttributeError: 'A' object has no attribute 'foo'
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-attribute)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1329)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1362)
 </details>
 
 ## `unresolved-import`
@@ -1499,7 +1536,7 @@ import foo  # ModuleNotFoundError: No module named 'foo'
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-import)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1351)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1384)
 </details>
 
 ## `unresolved-reference`
@@ -1523,7 +1560,7 @@ print(x)  # NameError: name 'x' is not defined
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-reference)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1370)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1403)
 </details>
 
 ## `unsupported-bool-conversion`
@@ -1559,7 +1596,7 @@ b1 < b2 < b1  # exception raised here
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unsupported-bool-conversion)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1063)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1096)
 </details>
 
 ## `unsupported-operator`
@@ -1586,7 +1623,7 @@ A() + A()  # TypeError: unsupported operand type(s) for +: 'A' and 'A'
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unsupported-operator)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1389)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1422)
 </details>
 
 ## `zero-stepsize-in-slice`
@@ -1610,7 +1647,7 @@ l[1:10:0]  # ValueError: slice step cannot be zero
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20zero-stepsize-in-slice)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1411)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1444)
 </details>
 
 ## `invalid-ignore-comment`
@@ -1666,7 +1703,7 @@ A.c  # AttributeError: type object 'A' has no attribute 'c'
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-unbound-attribute)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1115)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1148)
 </details>
 
 ## `possibly-unbound-implicit-call`
@@ -1697,7 +1734,7 @@ A()[0]  # TypeError: 'A' object is not subscriptable
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-unbound-implicit-call)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L112)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L113)
 </details>
 
 ## `possibly-unbound-import`
@@ -1728,7 +1765,7 @@ from module import a  # ImportError: cannot import name 'a' from 'module'
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-unbound-import)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1137)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1170)
 </details>
 
 ## `redundant-cast`
@@ -1754,7 +1791,7 @@ cast(int, f())  # Redundant
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20redundant-cast)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1482)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1515)
 </details>
 
 ## `undefined-reveal`
@@ -1777,7 +1814,7 @@ reveal_type(1)  # NameError: name 'reveal_type' is not defined
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20undefined-reveal)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1290)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1323)
 </details>
 
 ## `unknown-rule`
@@ -1845,7 +1882,7 @@ class D(C): ...  # error: [unsupported-base]
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unsupported-base)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L490)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L523)
 </details>
 
 ## `division-by-zero`
@@ -1868,7 +1905,7 @@ Dividing by zero raises a `ZeroDivisionError` at runtime.
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20division-by-zero)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L241)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L242)
 </details>
 
 ## `possibly-unresolved-reference`
@@ -1895,7 +1932,7 @@ print(x)  # NameError: name 'x' is not defined
 
 ### Links
 * [Related issues](https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-unresolved-reference)
-* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1163)
+* [View source](https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1196)
 </details>
 
 ## `unused-ignore-comment`
diff --git a/crates/ty_python_semantic/resources/mdtest/dataclasses.md b/crates/ty_python_semantic/resources/mdtest/dataclasses.md
index 699a624173..98d1af487d 100644
--- a/crates/ty_python_semantic/resources/mdtest/dataclasses.md
+++ b/crates/ty_python_semantic/resources/mdtest/dataclasses.md
@@ -715,6 +715,8 @@ asdict(Foo)
 
 ## `dataclasses.KW_ONLY`
 
+<!-- snapshot-diagnostics -->
+
 If an attribute is annotated with `dataclasses.KW_ONLY`, it is not added to the synthesized
 `__init__` of the class. Instead, this special marker annotation causes Python at runtime to ensure
 that all annotations following it have keyword-only parameters generated for them in the class's
@@ -727,6 +729,7 @@ python-version = "3.10"
 
 ```py
 from dataclasses import dataclass, field, KW_ONLY
+from typing_extensions import reveal_type
 
 @dataclass
 class C:
@@ -734,6 +737,8 @@ class C:
     _: KW_ONLY
     y: str
 
+reveal_type(C.__init__)  # revealed: (self: C, x: int, *, y: str) -> None
+
 # error: [missing-argument]
 # error: [too-many-positional-arguments]
 C(3, "")
@@ -746,14 +751,14 @@ runtime:
 
 ```py
 @dataclass
-class Fails:
+class Fails:  # error: [duplicate-kw-only]
     a: int
     b: KW_ONLY
     c: str
-
-    # TODO: we should emit an error here
-    # (two different names with `KW_ONLY` annotations in the same dataclass means the class fails at runtime)
     d: KW_ONLY
+    e: bytes
+
+reveal_type(Fails.__init__)  # revealed: (self: Fails, a: int, *, c: str, e: bytes) -> None
 ```
 
 ## Other special cases
diff --git a/crates/ty_python_semantic/resources/mdtest/snapshots/dataclasses.md_-_Dataclasses_-_`dataclasses.KW_ONLY…_(dd1b8f2f71487f16).snap b/crates/ty_python_semantic/resources/mdtest/snapshots/dataclasses.md_-_Dataclasses_-_`dataclasses.KW_ONLY…_(dd1b8f2f71487f16).snap
new file mode 100644
index 0000000000..7809b04a37
--- /dev/null
+++ b/crates/ty_python_semantic/resources/mdtest/snapshots/dataclasses.md_-_Dataclasses_-_`dataclasses.KW_ONLY…_(dd1b8f2f71487f16).snap
@@ -0,0 +1,114 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: dataclasses.md - Dataclasses - `dataclasses.KW_ONLY`
+mdtest path: crates/ty_python_semantic/resources/mdtest/dataclasses.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | from dataclasses import dataclass, field, KW_ONLY
+ 2 | from typing_extensions import reveal_type
+ 3 | 
+ 4 | @dataclass
+ 5 | class C:
+ 6 |     x: int
+ 7 |     _: KW_ONLY
+ 8 |     y: str
+ 9 | 
+10 | reveal_type(C.__init__)  # revealed: (self: C, x: int, *, y: str) -> None
+11 | 
+12 | # error: [missing-argument]
+13 | # error: [too-many-positional-arguments]
+14 | C(3, "")
+15 | 
+16 | C(3, y="")
+17 | @dataclass
+18 | class Fails:  # error: [duplicate-kw-only]
+19 |     a: int
+20 |     b: KW_ONLY
+21 |     c: str
+22 |     d: KW_ONLY
+23 |     e: bytes
+24 | 
+25 | reveal_type(Fails.__init__)  # revealed: (self: Fails, a: int, *, c: str, e: bytes) -> None
+```
+
+# Diagnostics
+
+```
+info[revealed-type]: Revealed type
+  --> src/mdtest_snippet.py:10:13
+   |
+ 8 |     y: str
+ 9 |
+10 | reveal_type(C.__init__)  # revealed: (self: C, x: int, *, y: str) -> None
+   |             ^^^^^^^^^^ `(self: C, x: int, *, y: str) -> None`
+11 |
+12 | # error: [missing-argument]
+   |
+
+```
+
+```
+error[missing-argument]: No argument provided for required parameter `y`
+  --> src/mdtest_snippet.py:14:1
+   |
+12 | # error: [missing-argument]
+13 | # error: [too-many-positional-arguments]
+14 | C(3, "")
+   | ^^^^^^^^
+15 |
+16 | C(3, y="")
+   |
+info: rule `missing-argument` is enabled by default
+
+```
+
+```
+error[too-many-positional-arguments]: Too many positional arguments: expected 1, got 2
+  --> src/mdtest_snippet.py:14:6
+   |
+12 | # error: [missing-argument]
+13 | # error: [too-many-positional-arguments]
+14 | C(3, "")
+   |      ^^
+15 |
+16 | C(3, y="")
+   |
+info: rule `too-many-positional-arguments` is enabled by default
+
+```
+
+```
+error[duplicate-kw-only]: Dataclass has more than one field annotated with `KW_ONLY`
+  --> src/mdtest_snippet.py:18:7
+   |
+16 | C(3, y="")
+17 | @dataclass
+18 | class Fails:  # error: [duplicate-kw-only]
+   |       ^^^^^
+19 |     a: int
+20 |     b: KW_ONLY
+   |
+info: `KW_ONLY` fields: `b`, `d`
+info: rule `duplicate-kw-only` is enabled by default
+
+```
+
+```
+info[revealed-type]: Revealed type
+  --> src/mdtest_snippet.py:25:13
+   |
+23 |     e: bytes
+24 |
+25 | reveal_type(Fails.__init__)  # revealed: (self: Fails, a: int, *, c: str, e: bytes) -> None
+   |             ^^^^^^^^^^^^^^ `(self: Fails, a: int, *, c: str, e: bytes) -> None`
+   |
+
+```
diff --git a/crates/ty_python_semantic/src/types/class.rs b/crates/ty_python_semantic/src/types/class.rs
index 4c729caee9..ca3d59220b 100644
--- a/crates/ty_python_semantic/src/types/class.rs
+++ b/crates/ty_python_semantic/src/types/class.rs
@@ -123,7 +123,7 @@ fn try_metaclass_cycle_initial<'db>(
 
 /// A category of classes with code generation capabilities (with synthesized methods).
 #[derive(Clone, Copy, Debug, PartialEq)]
-enum CodeGeneratorKind {
+pub(crate) enum CodeGeneratorKind {
     /// Classes decorated with `@dataclass` or similar dataclass-like decorators
     DataclassLike,
     /// Classes inheriting from `typing.NamedTuple`
@@ -131,7 +131,7 @@ enum CodeGeneratorKind {
 }
 
 impl CodeGeneratorKind {
-    fn from_class(db: &dyn Db, class: ClassLiteral<'_>) -> Option<Self> {
+    pub(crate) fn from_class(db: &dyn Db, class: ClassLiteral<'_>) -> Option<Self> {
         if CodeGeneratorKind::DataclassLike.matches(db, class) {
             Some(CodeGeneratorKind::DataclassLike)
         } else if CodeGeneratorKind::NamedTuple.matches(db, class) {
@@ -1322,7 +1322,7 @@ impl<'db> ClassLiteral<'db> {
                     .is_some_and(|instance| instance.class.is_known(db, KnownClass::KwOnly))
                 {
                     // Attributes annotated with `dataclass.KW_ONLY` are not present in the synthesized
-                    // `__init__` method, ; they only used to indicate that the parameters after this are
+                    // `__init__` method; they are used to indicate that the following parameters are
                     // keyword-only.
                     kw_only_field_seen = true;
                     continue;
@@ -1455,7 +1455,7 @@ impl<'db> ClassLiteral<'db> {
     /// Returns a list of all annotated attributes defined in this class, or any of its superclasses.
     ///
     /// See [`ClassLiteral::own_fields`] for more details.
-    fn fields(
+    pub(crate) fn fields(
         self,
         db: &'db dyn Db,
         specialization: Option<Specialization<'db>>,
diff --git a/crates/ty_python_semantic/src/types/diagnostic.rs b/crates/ty_python_semantic/src/types/diagnostic.rs
index f85d77dcff..f39adacf63 100644
--- a/crates/ty_python_semantic/src/types/diagnostic.rs
+++ b/crates/ty_python_semantic/src/types/diagnostic.rs
@@ -33,6 +33,7 @@ pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
     registry.register_lint(&CYCLIC_CLASS_DEFINITION);
     registry.register_lint(&DIVISION_BY_ZERO);
     registry.register_lint(&DUPLICATE_BASE);
+    registry.register_lint(&DUPLICATE_KW_ONLY);
     registry.register_lint(&INCOMPATIBLE_SLOTS);
     registry.register_lint(&INCONSISTENT_MRO);
     registry.register_lint(&INDEX_OUT_OF_BOUNDS);
@@ -277,6 +278,38 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for dataclass definitions with more than one field
+    /// annotated with `KW_ONLY`.
+    ///
+    /// ## Why is this bad?
+    /// `dataclasses.KW_ONLY` is a special marker used to
+    /// emulate the `*` syntax in normal signatures.
+    /// It can only be used once per dataclass.
+    ///
+    /// Attempting to annotate two different fields with
+    /// it will lead to a runtime error.
+    ///
+    /// ## Examples
+    /// ```python
+    /// from dataclasses import dataclass, KW_ONLY
+    ///
+    /// @dataclass
+    /// class A:  # Crash at runtime
+    ///     b: int
+    ///     _1: KW_ONLY
+    ///     c: str
+    ///     _2: KW_ONLY
+    ///     d: bytes
+    /// ```
+    pub(crate) static DUPLICATE_KW_ONLY = {
+        summary: "detects dataclass definitions with more than once usages of `KW_ONLY`",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for classes whose bases define incompatible `__slots__`.
diff --git a/crates/ty_python_semantic/src/types/infer.rs b/crates/ty_python_semantic/src/types/infer.rs
index 4f7180ee31..e57ddf8b31 100644
--- a/crates/ty_python_semantic/src/types/infer.rs
+++ b/crates/ty_python_semantic/src/types/infer.rs
@@ -74,13 +74,13 @@ use crate::semantic_index::{
 use crate::types::call::{
     Argument, Binding, Bindings, CallArgumentTypes, CallArguments, CallError,
 };
-use crate::types::class::{MetaclassErrorKind, SliceLiteral};
+use crate::types::class::{CodeGeneratorKind, MetaclassErrorKind, SliceLiteral};
 use crate::types::diagnostic::{
     self, CALL_NON_CALLABLE, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS,
-    CYCLIC_CLASS_DEFINITION, DIVISION_BY_ZERO, INCONSISTENT_MRO, INVALID_ARGUMENT_TYPE,
-    INVALID_ASSIGNMENT, INVALID_ATTRIBUTE_ACCESS, INVALID_BASE, INVALID_DECLARATION,
-    INVALID_GENERIC_CLASS, INVALID_LEGACY_TYPE_VARIABLE, INVALID_PARAMETER_DEFAULT,
-    INVALID_TYPE_ALIAS_TYPE, INVALID_TYPE_FORM, INVALID_TYPE_GUARD_CALL,
+    CYCLIC_CLASS_DEFINITION, DIVISION_BY_ZERO, DUPLICATE_KW_ONLY, INCONSISTENT_MRO,
+    INVALID_ARGUMENT_TYPE, INVALID_ASSIGNMENT, INVALID_ATTRIBUTE_ACCESS, INVALID_BASE,
+    INVALID_DECLARATION, INVALID_GENERIC_CLASS, INVALID_LEGACY_TYPE_VARIABLE,
+    INVALID_PARAMETER_DEFAULT, INVALID_TYPE_ALIAS_TYPE, INVALID_TYPE_FORM, INVALID_TYPE_GUARD_CALL,
     INVALID_TYPE_VARIABLE_CONSTRAINTS, POSSIBLY_UNBOUND_IMPLICIT_CALL, POSSIBLY_UNBOUND_IMPORT,
     TypeCheckDiagnostics, UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE, UNRESOLVED_IMPORT,
     UNRESOLVED_REFERENCE, UNSUPPORTED_OPERATOR, report_implicit_return_type,
@@ -1114,6 +1114,46 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                     }
                 }
             }
+
+            // (5) Check that a dataclass does not have more than one `KW_ONLY`.
+            if let Some(field_policy @ CodeGeneratorKind::DataclassLike) =
+                CodeGeneratorKind::from_class(self.db(), class)
+            {
+                let specialization = None;
+                let mut kw_only_field_names = vec![];
+
+                for (name, (attr_ty, _)) in class.fields(self.db(), specialization, field_policy) {
+                    let Some(instance) = attr_ty.into_nominal_instance() else {
+                        continue;
+                    };
+
+                    if !instance.class.is_known(self.db(), KnownClass::KwOnly) {
+                        continue;
+                    }
+
+                    kw_only_field_names.push(name);
+                }
+
+                if kw_only_field_names.len() > 1 {
+                    // TODO: The fields should be displayed in a subdiagnostic.
+                    if let Some(builder) = self
+                        .context
+                        .report_lint(&DUPLICATE_KW_ONLY, &class_node.name)
+                    {
+                        let mut diagnostic = builder.into_diagnostic(format_args!(
+                            "Dataclass has more than one field annotated with `KW_ONLY`"
+                        ));
+
+                        diagnostic.info(format_args!(
+                            "`KW_ONLY` fields: {}",
+                            kw_only_field_names
+                                .iter()
+                                .map(|name| format!("`{name}`"))
+                                .join(", ")
+                        ));
+                    }
+                }
+            }
         }
     }
 
diff --git a/ty.schema.json b/ty.schema.json
index e6b871ecdd..169000158b 100644
--- a/ty.schema.json
+++ b/ty.schema.json
@@ -341,6 +341,16 @@
             }
           ]
         },
+        "duplicate-kw-only": {
+          "title": "detects dataclass definitions with more than once usages of `KW_ONLY`",
+          "description": "## What it does\nChecks for dataclass definitions with more than one field\nannotated with `KW_ONLY`.\n\n## Why is this bad?\n`dataclasses.KW_ONLY` is a special marker used to\nemulate the `*` syntax in normal signatures.\nIt can only be used once per dataclass.\n\nAttempting to annotate two different fields with\nit will lead to a runtime error.\n\n## Examples\n```python\nfrom dataclasses import dataclass, KW_ONLY\n\n@dataclass\nclass A:  # Crash at runtime\n    b: int\n    _1: KW_ONLY\n    c: str\n    _2: KW_ONLY\n    d: bytes\n```",
+          "default": "error",
+          "oneOf": [
+            {
+              "$ref": "#/definitions/Level"
+            }
+          ]
+        },
         "escape-character-in-forward-annotation": {
           "title": "detects forward type annotations with escape characters",
           "description": "TODO #14889",