diff --git a/bowler/helpers.py b/bowler/helpers.py
index a31d2d0..9deb1e8 100644
--- a/bowler/helpers.py
+++ b/bowler/helpers.py
@@ -6,7 +6,8 @@
 # LICENSE file in the root directory of this source tree.
 
 import logging
-from typing import List, Optional, Sequence, Union
+from inspect import Signature
+from typing import TYPE_CHECKING, List, Optional, Sequence, Union
 
 import click
 from fissix.pgen2.token import tok_name
@@ -14,6 +15,9 @@
 
 from .types import LN, SYMBOL, TOKEN, Capture, Filename, FilenameMatcher
 
+if TYPE_CHECKING:
+    from .imr import FunctionSpec
+
 log = logging.getLogger(__name__)
 
 INDENT_STR = ".  "
@@ -144,6 +148,38 @@ def is_call_to(node: LN, func_name: str) -> bool:
     )
 
 
+def spec_contains_parameter_name(param_name: str, spec: "FunctionSpec") -> bool:
+    return param_name in (arg.name for arg in spec.arguments)
+
+
+def definition_contains_parameter(param_name: str, spec: "FunctionSpec") -> bool:
+    return spec_contains_parameter_name(param_name, spec)
+
+
+def callsite_contains_parameter(
+    param_name: str, spec: "FunctionSpec", function_sig: Signature
+) -> bool:
+    # Handle kwargs
+    if spec_contains_parameter_name(param_name, spec):
+        return True
+
+    # Handle positional args
+    if param_name not in function_sig.parameters:
+        raise ValueError(
+            f"Function signature must contain parameter we are looking for"
+        )
+
+    names = list(function_sig.parameters)
+    position = names.index(param_name)
+    if names[0] in ("self", "cls", "meta"):
+        position -= 1
+
+    if len(spec.arguments) <= position:
+        return False
+
+    return all(not arg.name and not arg.star for arg in spec.arguments[: position + 1])
+
+
 def find_first(node: LN, target: int, recursive: bool = False) -> Optional[LN]:
     queue: List[LN] = [node]
     queue.extend(node.children)
diff --git a/bowler/query.py b/bowler/query.py
index 16ae466..c3b670f 100644
--- a/bowler/query.py
+++ b/bowler/query.py
@@ -9,7 +9,7 @@
 import logging
 import pathlib
 import re
-from functools import wraps
+from functools import partial, wraps
 from typing import Any, Callable, Dict, List, Optional, Type, TypeVar, Union, cast
 
 from attr import Factory, dataclass
@@ -19,6 +19,8 @@
 
 from .helpers import (
     Once,
+    callsite_contains_parameter,
+    definition_contains_parameter,
     dotted_parts,
     find_first,
     find_last,
@@ -438,6 +440,42 @@ def filter_is_call(node: LN, capture: Capture, filename: Filename) -> bool:
         self.current.filters.append(filter_is_call)
         return self
 
+    def filter_contains_parameter(
+        self, param_name: str, node: LN, capture: Capture, filename: Filename
+    ) -> bool:
+        transform = self.current
+        if transform.selector not in ("function", "method"):
+            raise ValueError(
+                "parameter presence filter must follow select_function/select_method"
+            )
+        if "source" not in transform.kwargs:
+            raise ValueError(
+                "Determining if parameter is present requires passing original function"
+            )
+
+        if "function_def" in capture or "class_def" in capture:
+            spec = FunctionSpec.build(node, capture)
+            return definition_contains_parameter(param_name, spec)
+        if "function_call" in capture or "class_call" in capture:
+            spec = FunctionSpec.build(node, capture)
+            sig = inspect.signature(transform.kwargs["source"])
+            return callsite_contains_parameter(param_name, spec, sig)
+
+        return False
+
+    def contains_parameter(self, name: str) -> "Query":
+        self.current.filters.append(partial(self.filter_contains_parameter, name))
+        return self
+
+    def missing_parameter(self, name: str) -> "Query":
+        def filter_missing_parameter(
+            node: LN, capture: Capture, filename: Filename
+        ) -> bool:
+            return not self.filter_contains_parameter(name, node, capture, filename)
+
+        self.current.filters.append(filter_missing_parameter)
+        return self
+
     def is_def(self) -> "Query":
         def filter_is_def(node: LN, capture: Capture, filename: Filename) -> bool:
             return bool("function_def" in capture or "class_def" in capture)
@@ -748,6 +786,10 @@ def add_argument_transform(
             value_leaf = Name(value)
 
             if spec.is_def:
+                if definition_contains_parameter(name, spec):
+                    raise ValueError(
+                        f"{name} is already present in the definition of {spec.name}"
+                    )
                 new_arg = FunctionArgument(
                     name,
                     value_leaf if keyword else None,
@@ -772,6 +814,12 @@ def add_argument_transform(
                     spec.arguments.append(new_arg)
 
             elif positional:
+                if after not in (SENTINEL, START):
+                    sig = inspect.signature(transform.kwargs["source"])
+                    if callsite_contains_parameter(name, spec, sig):
+                        raise ValueError(
+                            f"{name} is already present in the callsite of {spec.name}"
+                        )
                 new_arg = FunctionArgument(value=value_leaf)
                 for index, argument in enumerate(spec.arguments):
                     if argument.star and argument.star.type == TOKEN.STAR:
@@ -792,6 +840,29 @@ def add_argument_transform(
                 if not done:
                     spec.arguments.append(new_arg)
 
+            else:
+                if "source" not in transform.kwargs:
+                    raise ValueError(
+                        "Adding a positional arg to a callsite requires passing "
+                        "original function"
+                    )
+
+                sig = inspect.signature(transform.kwargs["source"])
+                if callsite_contains_parameter(name, spec, sig):
+                    raise ValueError(
+                        f"{name} is already present in the callsite of {spec.name}"
+                    )
+
+                # Drop kwarg at end of call to avoid breaking positional args
+                new_arg = FunctionArgument(name=name, value=value_leaf)
+
+                # Double star should only ever be present at the end of a call
+                star_arg = spec.arguments[-1].star if spec.arguments else None
+                if star_arg and star_arg.type == TOKEN.DOUBLESTAR:
+                    spec.arguments.insert(-1, new_arg)
+                else:
+                    spec.arguments.append(new_arg)
+
             spec.explode()
 
         transform.callbacks.append(add_argument_transform)
diff --git a/bowler/tests/query.py b/bowler/tests/query.py
index 94df5d1..05d320b 100644
--- a/bowler/tests/query.py
+++ b/bowler/tests/query.py
@@ -122,6 +122,57 @@ def query_func(x):
             query_func=query_func,
         )
 
+    def test_filter_contains_parameter(self):
+        def f(x, y):
+            pass
+
+        def query_func(x):
+            return Query(x).select_function(f).contains_parameter("y").rename("g")
+
+        self.run_bowler_modifiers(
+            [
+                ("def f(x, y):\n   pass", "def g(x, y):\n   pass"),
+                ("def f(x, y, z):\n   pass", "def g(x, y, z):\n   pass"),
+                ("def f(x):\n   pass", "def f(x):\n   pass"),
+                ("def x(y):\n   pass", "def x(y):\n   pass"),
+                ("def f(*_):\n   pass", "def f(*_):\n   pass"),
+                ("def f(**_):\n   pass", "def f(**_):\n   pass"),
+                ("f(1, y=2)", "g(1, y=2)"),
+                ("f(1, 2)", "g(1, 2)"),
+                ("f(1, 2, z=3)", "g(1, 2, z=3)"),
+                ("f(y=2)", "g(y=2)"),
+                ("f(x=2, **a)", "f(x=2, **a)"),
+                ("f(*a, **a)", "f(*a, **a)"),
+                ("f(*_)", "f(*_)"),
+                ("f(**_)", "f(**_)"),
+                ("f(x=1)", "f(x=1)"),
+                ("f(1)", "f(1)"),
+                ("f(1, x=2)", "f(1, x=2)"),
+            ],
+            query_func=query_func,
+        )
+
+    def test_filter_missing_parameter(self):
+        def f(x, y):
+            pass
+
+        def query_func(x):
+            return Query(x).select_function(f).missing_parameter("y").rename("g")
+
+        self.run_bowler_modifiers(
+            [
+                ("def f(x, z):\n   pass", "def g(x, z):\n   pass"),
+                ("def f(x, y, z):\n   pass", "def f(x, y, z):\n   pass"),
+                ("f(1, z=2)", "g(1, z=2)"),
+                ("f(1)", "g(1)"),
+                ("f(x=2, **a)", "g(x=2, **a)"),
+                ("f(*a, **a)", "g(*a, **a)"),
+                ("f(1, 2, z=3)", "f(1, 2, z=3)"),
+                ("f(y=2)", "f(y=2)"),
+            ],
+            query_func=query_func,
+        )
+
     def test_filter_in_class(self):
         def query_func_bar(x):
             return Query(x).select_function("f").in_class("Bar", False).rename("g")
@@ -172,19 +223,92 @@ def query_func_foo_subclasses(x):
             [("def f(): pass", "def f(): pass")], query_func=query_func_bar
         )
 
-    def test_add_argument(self):
+    def test_add_keyword_argument(self):
+        def f(z, x):
+            pass
+
+        def def_query_func(x):
+            return Query(x).select_function(f).is_def().add_argument("y", "5")
+
+        def call_query_func(x):
+            return Query(x).select_function(f).is_call().add_argument("x", "5")
+
+        def conditional_call_query_func(x):
+            return (
+                Query(x)
+                .select_function(f)
+                .is_call()
+                .missing_parameter("x")
+                .add_argument("x", "5")
+            )
+
+        # Definition kwarg tests
+        self.run_bowler_modifiers(
+            [
+                ("def f(z, x): pass", "def f(z, x, y=5): pass"),
+                ("def g(x): pass", "def g(x): pass"),
+            ],
+            query_func=def_query_func,
+        )
+        with self.assertRaises(AssertionError):
+            self.run_bowler_modifier("def f(z, x, y): pass", query_func=def_query_func)
+
+        # Callsite kwarg tests
+        self.run_bowler_modifiers(
+            [
+                ("f(1)", "f(1, x=5)"),
+                ("f(z=1)", "f(z=1, x=5)"),
+                ("f(z=1, **a)", "f(z=1, x=5, **a)"),
+                ("g()", "g()"),
+            ],
+            query_func=call_query_func,
+        )
+        with self.assertRaises(AssertionError):
+            self.run_bowler_modifier("f(1, 2)", query_func=call_query_func)
+
+        # Conditional callsite kwarg tests
+        self.run_bowler_modifiers(
+            [
+                ("f(1)", "f(1, x=5)"),
+                ("f(1, 2)", "f(1, 2)"),
+                ("f(z=1)", "f(z=1, x=5)"),
+                ("f(z=1, x=2)", "f(z=1, x=2)"),
+                ("f(z=1, **a)", "f(z=1, x=5, **a)"),
+                ("f(z=1, x=2)", "f(z=1, x=2)"),
+                ("f(z=1, **a)", "f(z=1, x=5, **a)"),
+                ("g()", "g()"),
+            ],
+            query_func=conditional_call_query_func,
+        )
+
+    def test_add_positional_argument(self):
         def query_func(x):
-            return Query(x).select_function("f").add_argument("y", "5")
+            return Query(x).select_function("f").add_argument("y", "5", True)
 
         self.run_bowler_modifiers(
             [
-                ("def f(x): pass", "def f(x, y=5): pass"),
+                ("def f(x): pass", "def f(x, y): pass"),
                 ("def g(x): pass", "def g(x): pass"),
-                # ("f()", "???"),
+                ("f()", "f(5)"),
                 ("g()", "g()"),
             ],
+            query_func=conditional_call_query_func,
+        )
+
+    def test_add_positional_argument(self):
+        def query_func(x):
+            return Query(x).select_function("f").add_argument("y", "5", True)
+
+        self.run_bowler_modifiers(
+            [
+                ("def f(x): pass", "def f(x, y): pass"),
+                ("def g(x): pass", "def g(x): pass"),
+                ("f()", "f(5)"),
+            ],
             query_func=query_func,
         )
+        with self.assertRaises(AssertionError):
+            self.run_bowler_modifier("def f(x, y): pass", query_func=query_func)
 
     def test_modifier_return_value(self):
         input = "a+b"
diff --git a/docs/api-modifiers.md b/docs/api-modifiers.md
index 63ad96e..7d497d4 100644
--- a/docs/api-modifiers.md
+++ b/docs/api-modifiers.md
@@ -70,9 +70,7 @@ new_name | New name for element.
 
 ### `.add_argument()`
 
-Add an argument to a function or method, as well as callers. For positional arguments,
-the default value will be used to update all callers; for keyword arguments, it will
-be used in the function definition.
+Add an argument to a function or method, as well as callers.
 
 Requires use of [`.select_function`](api-selectors#select-function) or
 [`.select_method`](api-selectors#select-method).