diff --git a/benches/parser.rs b/benches/parser.rs
index 2f8db70..4d39b52 100644
--- a/benches/parser.rs
+++ b/benches/parser.rs
@@ -41,19 +41,15 @@ fn graphql_ast_print_graphql_query_rs(bench: &mut Bencher) {
     bench.iter(|| ast.print());
 }
 
-
-
 fn graphql_ast_print_gql_parser(bench: &mut Bencher) {
     use graphql_parser::query::parse_query;
     let ast = parse_query::<&str>(QUERY).ok().unwrap();
-    bench.iter(|| {
-        ast.to_string()
-    });
+    bench.iter(|| ast.to_string());
 }
 
 fn graphql_ast_print_apollo_parser(bench: &mut Bencher) {
-    use apollo_parser::Parser;
     use apollo_parser::cst::CstNode;
+    use apollo_parser::Parser;
     let parser = Parser::new(QUERY);
     let cst = parser.parse();
     let doc = cst.document();
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index f3afee4..badf8a5 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -1,7 +1,7 @@
 pub use super::ast_conversion::*;
 use crate::error::{Error, ErrorType, Result};
 use bumpalo::collections::CollectIn;
-use hashbrown::{HashMap, hash_map::DefaultHashBuilder};
+use hashbrown::{hash_map::DefaultHashBuilder, HashMap};
 
 /// A context for a GraphQL document which holds an arena allocator.
 ///
diff --git a/src/ast/ast_conversion.rs b/src/ast/ast_conversion.rs
index a92b847..c97e2c0 100644
--- a/src/ast/ast_conversion.rs
+++ b/src/ast/ast_conversion.rs
@@ -1,6 +1,6 @@
 // #![allow(clippy::needless_update)]
-use bumpalo::collections::{vec::IntoIter, Vec};
 use super::ast::*;
+use bumpalo::collections::{vec::IntoIter, Vec};
 
 // TODO: from_iter_in could be a good helper here as well
 
@@ -75,7 +75,7 @@ impl<'a> DefaultIn<'a> for Document<'a> {
     fn default_in(arena: &'a bumpalo::Bump) -> Self {
         Document {
             definitions: Vec::new_in(&arena),
-            size_hint: 0
+            size_hint: 0,
         }
     }
 }
diff --git a/src/ast/mod.rs b/src/ast/mod.rs
index 1a31781..61e1f81 100644
--- a/src/ast/mod.rs
+++ b/src/ast/mod.rs
@@ -37,7 +37,7 @@ mod parser;
 mod printer;
 
 pub use ast::*;
-pub use ast_kind::ASTKind;
 pub use ast_conversion::DefaultIn;
+pub use ast_kind::ASTKind;
 pub use parser::ParseNode;
 pub use printer::PrintNode;
diff --git a/src/json/values.rs b/src/json/values.rs
index 88d2d10..748ecb0 100644
--- a/src/json/values.rs
+++ b/src/json/values.rs
@@ -287,7 +287,7 @@ mod tests {
                 name: "Int",
             }))),
             default_value: Value::Null,
-            directives: Directives::default_in(&ctx.arena)
+            directives: Directives::default_in(&ctx.arena),
         }];
 
         let var_defs = VariableDefinitions {
@@ -313,7 +313,7 @@ mod tests {
                 name: "orderByInput",
             })),
             default_value: Value::Null,
-            directives: Directives::default_in(&ctx.arena)
+            directives: Directives::default_in(&ctx.arena),
         }];
 
         let var_defs = VariableDefinitions {
diff --git a/src/validate/rules/mod.rs b/src/validate/rules/mod.rs
index e6a2090..3d9b9c3 100644
--- a/src/validate/rules/mod.rs
+++ b/src/validate/rules/mod.rs
@@ -1,10 +1,14 @@
 use crate::visit::ComposedVisitor;
 
+// Missing schemaless rules
+// https://github.com/graphql/graphql-js/blob/main/src/validation/rules/DeferStreamDirectiveLabelRule.ts
+// https://github.com/graphql/graphql-js/blob/main/src/validation/rules/DeferStreamDirectiveOnValidOperationsRule.ts
 mod known_fragment_names;
 mod lone_anonymous_operation;
 mod no_fragment_cycles;
 mod no_undefined_variables;
 mod no_unused_fragments;
+mod no_unused_variables;
 mod unique_argument_names;
 mod unique_fragment_names;
 mod unique_operation_names;
@@ -16,6 +20,7 @@ pub use lone_anonymous_operation::*;
 pub use no_fragment_cycles::*;
 pub use no_undefined_variables::*;
 pub use no_unused_fragments::*;
+pub use no_unused_variables::*;
 pub use unique_argument_names::*;
 pub use unique_fragment_names::*;
 pub use unique_operation_names::*;
@@ -51,7 +56,12 @@ pub type DefaultRules<'a> = ComposedVisitor<
                 'a,
                 ValidationContext<'a>,
                 NoFragmentCycles<'a>,
-                NoUndefinedVariables<'a>,
+                ComposedVisitor<
+                    'a,
+                    ValidationContext<'a>,
+                    NoUndefinedVariables<'a>,
+                    NoUnusedVariables<'a>,
+                >,
             >,
         >,
     >,
diff --git a/src/validate/rules/no_unused_variables.rs b/src/validate/rules/no_unused_variables.rs
new file mode 100644
index 0000000..0405f9f
--- /dev/null
+++ b/src/validate/rules/no_unused_variables.rs
@@ -0,0 +1,94 @@
+use bumpalo::collections::Vec;
+
+use super::super::{ValidationContext, ValidationRule};
+use crate::{ast::*, visit::*};
+
+/// Validate that a document uses all the variables it defines at least once.
+///
+/// See [`ValidationRule`]
+/// [Reference](https://spec.graphql.org/draft/#sec-All-Variables-Used)
+pub struct NoUnusedVariables<'a> {
+    variables: Vec<'a, &'a str>,
+    used_variables: Vec<'a, &'a str>,
+}
+
+impl<'a> DefaultIn<'a> for NoUnusedVariables<'a> {
+    fn default_in(arena: &'a bumpalo::Bump) -> Self {
+        Self {
+            variables: Vec::new_in(arena),
+            used_variables: Vec::new_in(arena),
+        }
+    }
+}
+
+impl<'a> ValidationRule<'a> for NoUnusedVariables<'a> {}
+
+impl<'a> Visitor<'a, ValidationContext<'a>> for NoUnusedVariables<'a> {
+    fn enter_operation(
+        &mut self,
+        _ctx: &mut ValidationContext<'a>,
+        operation: &'a OperationDefinition<'a>,
+        _info: &VisitInfo,
+    ) -> VisitFlow {
+        operation
+            .variable_definitions
+            .children
+            .iter()
+            .for_each(|def| {
+                self.variables.push(def.variable.name);
+            });
+        VisitFlow::Next
+    }
+
+    fn enter_field(
+        &mut self,
+        _ctx: &mut ValidationContext<'a>,
+        field: &'a Field<'a>,
+        _info: &VisitInfo,
+    ) -> VisitFlow {
+        field.arguments.children.iter().for_each(|arg| {
+            if let Value::Variable(var) = arg.value {
+                self.used_variables.push(var.name);
+            }
+        });
+        VisitFlow::Next
+    }
+
+    fn leave_document(
+        &mut self,
+        ctx: &mut ValidationContext<'a>,
+        _document: &'a Document<'a>,
+        _info: &VisitInfo,
+    ) -> VisitFlow {
+        self.variables.iter().for_each(|defined_variable| {
+            if !self.used_variables.contains(defined_variable) {
+                ctx.add_error("All defined variables must be at least used once");
+            }
+        });
+        VisitFlow::Next
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn used_all_variables() {
+        let ctx = ASTContext::new();
+        let document =
+            Document::parse(&ctx, "query ($x: Int!) { todos(from: $x) { id } }").unwrap();
+        NoUnusedVariables::validate(&ctx, document).unwrap();
+    }
+
+    #[test]
+    fn has_unused_variable() {
+        let ctx = ASTContext::new();
+        let document = Document::parse(
+            &ctx,
+            "query ($x: Int!, $unused: String!) { todos(from: $x) { id } }",
+        )
+        .unwrap();
+        NoUnusedVariables::validate(&ctx, document).unwrap_err();
+    }
+}
diff --git a/src/validate/rules/validate.rs b/src/validate/rules/validate.rs
index e69de29..8b13789 100644
--- a/src/validate/rules/validate.rs
+++ b/src/validate/rules/validate.rs
@@ -0,0 +1 @@
+
diff --git a/src/validate/validate.rs b/src/validate/validate.rs
index 5affb40..47e8aea 100644
--- a/src/validate/validate.rs
+++ b/src/validate/validate.rs
@@ -33,7 +33,6 @@ where
     #[inline]
     fn default_in(arena: &'a bumpalo::Bump) -> Self {
         ComposedVisitor::new(A::default_in(arena), B::default_in(arena))
-        
     }
 }
 
diff --git a/src/visit/folder.rs b/src/visit/folder.rs
index 68ba5f7..78d1a09 100644
--- a/src/visit/folder.rs
+++ b/src/visit/folder.rs
@@ -1030,14 +1030,14 @@ mod tests {
             if selection_set.is_empty() {
                 return Ok(selection_set);
             }
-    
+
             let has_typename = selection_set.selections.iter().any(|selection| {
                 selection
                     .field()
                     .map(|field| field.name == "__typename" && field.alias.is_none())
                     .unwrap_or(false)
             });
-    
+
             if !has_typename {
                 let typename_field = Selection::Field(Field {
                     alias: None,
@@ -1046,13 +1046,16 @@ mod tests {
                     directives: Directives::default_in(&ctx.arena),
                     selection_set: SelectionSet::default_in(&ctx.arena),
                 });
-            
-              let new_selections = selection_set
-                .into_iter()
-                .chain(iter::once(typename_field))
-                .collect_in::<bumpalo::collections::Vec<Selection>>(&ctx.arena);
-    
-                Ok(SelectionSet { selections: new_selections })
+
+                let new_selections =
+                    selection_set
+                        .into_iter()
+                        .chain(iter::once(typename_field))
+                        .collect_in::<bumpalo::collections::Vec<Selection>>(&ctx.arena);
+
+                Ok(SelectionSet {
+                    selections: new_selections,
+                })
             } else {
                 Ok(selection_set)
             }
@@ -1066,8 +1069,7 @@ mod tests {
         let ast = Document::parse(&ctx, query).unwrap();
 
         let mut folder = AddTypenames {};
-        let new_ast = ast
-            .fold_operation(&ctx, None, &mut folder);
+        let new_ast = ast.fold_operation(&ctx, None, &mut folder);
         assert_eq!(
             new_ast.unwrap().print(),
             "{\n  todo {\n    id\n    author {\n      id\n      __typename\n    }\n    __typename\n  }\n  __typename\n}"