diff --git a/rule-tests/__snapshots__/unused-parameter-snapshot.yml b/rule-tests/__snapshots__/unused-parameter-snapshot.yml
new file mode 100644
index 0000000..695bdf2
--- /dev/null
+++ b/rule-tests/__snapshots__/unused-parameter-snapshot.yml
@@ -0,0 +1,56 @@
+id: unused-parameter
+snapshots:
+  'function foo(x: uint8) {}':
+    labels:
+    - source: x
+      style: primary
+      start: 13
+      end: 14
+    - source: foo
+      style: secondary
+      start: 9
+      end: 12
+    - source: '{}'
+      style: secondary
+      start: 23
+      end: 25
+    - source: 'function foo(x: uint8) {}'
+      style: secondary
+      start: 0
+      end: 25
+  'function foo(x: uint8, y: uint8) { x; }':
+    labels:
+    - source: y
+      style: primary
+      start: 23
+      end: 24
+    - source: x
+      style: secondary
+      start: 13
+      end: 14
+    - source: '{ x; }'
+      style: secondary
+      start: 33
+      end: 39
+    - source: 'function foo(x: uint8, y: uint8) { x; }'
+      style: secondary
+      start: 0
+      end: 39
+  'function foo(x: uint8, y: uint8) {}':
+    labels:
+    - source: x
+      style: primary
+      start: 13
+      end: 14
+    - source: foo
+      style: secondary
+      start: 9
+      end: 12
+    - source: '{}'
+      style: secondary
+      start: 33
+      end: 35
+    - source: 'function foo(x: uint8, y: uint8) {}'
+      style: secondary
+      start: 0
+      end: 35
diff --git a/rule-tests/unused-parameter-test.yml b/rule-tests/unused-parameter-test.yml
new file mode 100644
index 0000000..4f58583
--- /dev/null
+++ b/rule-tests/unused-parameter-test.yml
@@ -0,0 +1,10 @@
+id: unused-parameter
+valid:
+  - "function foo() {}"
+  - "function foo(x: uint8) { x; }"
+  - "function foo(x: uint8, y: uint8) { x; y; }"
+  - "function foo(x: uint8, y: uint8);"
+invalid:
+  - "function foo(x: uint8) {}"
+  - "function foo(x: uint8, y: uint8) { x; }"
+  - "function foo(x: uint8, y: uint8) {}"
diff --git a/rules/unused-parameter.yml b/rules/unused-parameter.yml
new file mode 100644
index 0000000..04cd14c
--- /dev/null
+++ b/rules/unused-parameter.yml
@@ -0,0 +1,25 @@
+id: unused-parameter
+message: Parameter is not used
+severity: error
+language: spicy
+rule:
+  kind: "ident"
+  pattern: $ID
+  all:
+    # Reject the original function ident. All parameter idents follow it, but
+    # it doesn't follow anything itself.
+    - follows:
+        kind: "ident"
+        stopBy: end
+
+    - inside:
+        kind: "function_decl"
+        all:
+          - has:
+              kind: "block"
+          - not:
+              has:
+                kind: "block"
+                has:
+                  pattern: $ID
+                  stopBy: end