diff --git a/Cargo.lock b/Cargo.lock
index 0d567fd..12364b7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -148,7 +148,7 @@ dependencies = [
 
 [[package]]
 name = "ethereum-rpc"
-version = "0.3.0"
+version = "0.3.1"
 dependencies = [
  "reqwest",
  "reqwest-enum",
@@ -749,7 +749,7 @@ dependencies = [
 
 [[package]]
 name = "reqwest-enum"
-version = "0.3.0"
+version = "0.3.1"
 dependencies = [
  "futures",
  "reqwest",
diff --git a/Cargo.toml b/Cargo.toml
index 6dcbf9a..7e394e4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,5 +1,5 @@
 [workspace]
-package.version = "0.3.0"
+package.version = "0.3.1"
 package.edition = "2021"
 package.documentation = "https://docs.rs/reqwest_enum"
 package.authors = ["Tao Xu <hi@hewig.dev>"]
diff --git a/reqwest-enum/src/provider.rs b/reqwest-enum/src/provider.rs
index ac58fcb..3fdf979 100644
--- a/reqwest-enum/src/provider.rs
+++ b/reqwest-enum/src/provider.rs
@@ -43,12 +43,12 @@ pub trait JsonRpcProviderType<T: Target>: ProviderType<T> {
 }
 
 pub type EndpointFn<T> = fn(target: &T) -> String;
-pub type RequestBuilderFn =
-    fn(request_builder: &reqwest::RequestBuilder) -> reqwest::RequestBuilder;
+pub type RequestBuilderFn<T> =
+    fn(request_builder: &reqwest::RequestBuilder, target: &T) -> reqwest::RequestBuilder;
 pub struct Provider<T: Target> {
     /// endpoint closure to customize the endpoint (url / path)
     endpoint_fn: Option<EndpointFn<T>>,
-    request_fn: Option<RequestBuilderFn>,
+    request_fn: Option<RequestBuilderFn<T>>,
     client: Client,
 }
 
@@ -166,7 +166,10 @@ impl<T> Provider<T>
 where
     T: Target,
 {
-    pub fn new(endpoint_fn: Option<EndpointFn<T>>, request_fn: Option<RequestBuilderFn>) -> Self {
+    pub fn new(
+        endpoint_fn: Option<EndpointFn<T>>,
+        request_fn: Option<RequestBuilderFn<T>>,
+    ) -> Self {
         let client = reqwest::Client::new();
         Self {
             client,
@@ -206,7 +209,7 @@ where
             }
         }
         if let Some(request_fn) = &self.request_fn {
-            request = request_fn(&mut request);
+            request = request_fn(&mut request, target);
         }
         request
     }
@@ -233,7 +236,9 @@ mod tests {
         target::Target,
     };
     use serde::{Deserialize, Serialize};
+    use std::collections::hash_map::DefaultHasher;
     use std::collections::HashMap;
+    use std::hash::{Hash, Hasher};
     use tokio_test::block_on;
     #[derive(Serialize, Deserialize)]
     struct Person {
@@ -270,7 +275,7 @@ mod tests {
         }
 
         fn query(&self) -> HashMap<&'static str, &'static str> {
-            HashMap::default()
+            HashMap::from([("foo", "bar")])
         }
 
         fn headers(&self) -> HashMap<&'static str, &'static str> {
@@ -313,11 +318,15 @@ mod tests {
     fn test_request_fn() {
         let provider = Provider::<HttpBin>::new(
             None,
-            Some(|builder: &reqwest::RequestBuilder| {
-                builder
-                    .try_clone()
-                    .expect("trying to clone request")
-                    .header("X-test", "test")
+            Some(|builder: &reqwest::RequestBuilder, target: &HttpBin| {
+                let mut hasher = DefaultHasher::new();
+                target.query_string().hash(&mut hasher);
+                let hash = hasher.finish();
+
+                let mut req = builder.try_clone().expect("trying to clone request");
+                req = req.header("X-test", "test");
+                req = req.header("X-hash", format!("{}", hash));
+                req
             }),
         );
 
@@ -326,6 +335,7 @@ mod tests {
 
         assert_eq!(request.method().to_string(), "GET");
         assert_eq!(headers.get("X-test").unwrap(), "test");
+        assert_eq!(headers.get("X-hash").unwrap(), "3270317559611782182");
     }
 
     #[test]