diff --git a/Cargo.lock b/Cargo.lock
index 7c21d09..c4be405 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -8612,6 +8612,7 @@ dependencies = [
  "thiserror 1.0.69",
  "tokio",
  "tokio-test",
+ "tower 0.5.2",
  "tracing",
  "tracing-subscriber",
  "worker",
diff --git a/Cargo.toml b/Cargo.toml
index a7309db..eb99783 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,7 @@ members = [
     "rig-qdrant",
     "rig-core/rig-core-derive",
     "rig-sqlite",
-    "rig-eternalai", "rig-fastembed",
+    "rig-eternalai",
+    "rig-fastembed",
     "rig-surrealdb",
 ]
diff --git a/rig-core/Cargo.toml b/rig-core/Cargo.toml
index cedf63c..d31ac99 100644
--- a/rig-core/Cargo.toml
+++ b/rig-core/Cargo.toml
@@ -39,6 +39,7 @@ bytes = "1.9.0"
 async-stream = "0.3.6"
 mime_guess = { version = "2.0.5" }
 base64 = { version = "0.22.1" }
+tower = "0.5.2"
 
 
 [dev-dependencies]
diff --git a/rig-core/examples/tower.rs b/rig-core/examples/tower.rs
new file mode 100644
index 0000000..f1643d1
--- /dev/null
+++ b/rig-core/examples/tower.rs
@@ -0,0 +1,80 @@
+use rig::{
+    completion::{CompletionRequestBuilder, ToolDefinition},
+    middlewares::{
+        completion::{CompletionLayer, CompletionService},
+        tools::ToolLayer,
+    },
+    providers::openai::Client,
+    tool::{Tool, ToolSet},
+};
+use serde::{Deserialize, Serialize};
+use tower::Service;
+use tower::ServiceBuilder;
+
+#[tokio::main]
+async fn main() {
+    let client = Client::from_env();
+    let model = client.completion_model("gpt-4o");
+
+    let comp_layer = CompletionLayer::builder(model.clone()).build();
+    let tool_layer = ToolLayer::new(ToolSet::from_tools(vec![Add]));
+    let service = CompletionService::new(model.clone());
+
+    let mut service = ServiceBuilder::new()
+        .layer(comp_layer)
+        .layer(tool_layer)
+        .service(service);
+
+    let comp_request = CompletionRequestBuilder::new(model, "Please calculate 5+5 for me").build();
+
+    let res = service.call(comp_request).await.unwrap();
+
+    println!("{res:?}");
+}
+
+#[derive(Deserialize, Serialize)]
+struct Add;
+
+#[derive(Debug, thiserror::Error)]
+#[error("Math error")]
+struct MathError;
+
+#[derive(Deserialize)]
+struct OperationArgs {
+    x: i32,
+    y: i32,
+}
+
+impl Tool for Add {
+    const NAME: &'static str = "add";
+
+    type Error = MathError;
+    type Args = OperationArgs;
+    type Output = i32;
+
+    async fn definition(&self, _prompt: String) -> ToolDefinition {
+        serde_json::from_value(serde_json::json!({
+            "name": "add",
+            "description": "Add x and y together",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "x": {
+                        "type": "number",
+                        "description": "The first number to add"
+                    },
+                    "y": {
+                        "type": "number",
+                        "description": "The second number to add"
+                    }
+                }
+            }
+        }))
+        .expect("Tool Definition")
+    }
+
+    async fn call(&self, args: Self::Args) -> Result<Self::Output, Self::Error> {
+        let result = args.x + args.y;
+        Ok(result)
+    }
+}
diff --git a/rig-core/src/completion/request.rs b/rig-core/src/completion/request.rs
index 9a31fae..60456b0 100644
--- a/rig-core/src/completion/request.rs
+++ b/rig-core/src/completion/request.rs
@@ -235,6 +235,7 @@ pub trait CompletionModel: Clone + Send + Sync {
 }
 
 /// Struct representing a general completion request that can be sent to a completion model provider.
+#[derive(Clone)]
 pub struct CompletionRequest {
     /// The prompt to be sent to the completion model provider
     pub prompt: Message,
diff --git a/rig-core/src/lib.rs b/rig-core/src/lib.rs
index 300c962..a13d184 100644
--- a/rig-core/src/lib.rs
+++ b/rig-core/src/lib.rs
@@ -91,6 +91,7 @@ pub mod extractor;
 pub mod image_generation;
 pub(crate) mod json_utils;
 pub mod loaders;
+pub mod middlewares;
 pub mod one_or_many;
 pub mod pipeline;
 pub mod providers;
diff --git a/rig-core/src/middlewares/build_completions.rs b/rig-core/src/middlewares/build_completions.rs
new file mode 100644
index 0000000..f2d626d
--- /dev/null
+++ b/rig-core/src/middlewares/build_completions.rs
@@ -0,0 +1,532 @@
+use std::{future::Future, pin::Pin, task::Poll};
+use tower::{Layer, Service};
+
+use crate::{
+    completion::{
+        CompletionModel, CompletionRequest, CompletionRequestBuilder, Document, ToolDefinition,
+    },
+    message::Message,
+};
+
+/// A Tower layer to finish building your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct FinishBuilding;
+
+impl<S> Layer<S> for FinishBuilding {
+    type Service = FinishBuildingService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        FinishBuildingService { inner }
+    }
+}
+
+/// A Tower layer to finish building your `CompletionRequestBuilder`.
+/// Not intended to be used directly. Use [`FinishBuilding`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct FinishBuildingService<S> {
+    inner: S,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for FinishBuildingService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequest;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.build())
+        })
+    }
+}
+
+/// A Tower layer to add documents to your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct DocumentsLayer {
+    documents: Vec<Document>,
+}
+
+impl DocumentsLayer {
+    pub fn new(documents: Vec<Document>) -> Self {
+        Self { documents }
+    }
+}
+
+impl<S> Layer<S> for DocumentsLayer {
+    type Service = DocumentsLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        DocumentsLayerService {
+            inner,
+            documents: self.documents.clone(),
+        }
+    }
+}
+
+/// A Tower service to add documents to your `CompletionRequestBuilder`.
+/// Not intended to be used directly - use [`DocumentsLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct DocumentsLayerService<S> {
+    inner: S,
+    documents: Vec<Document>,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for DocumentsLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let documents = self.documents.clone();
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.documents(documents))
+        })
+    }
+}
+
+/// A Tower layer to add a temperature value to your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct TemperatureLayer {
+    temperature: f64,
+}
+
+impl TemperatureLayer {
+    pub fn new(temperature: f64) -> Self {
+        Self { temperature }
+    }
+}
+
+impl<S> Layer<S> for TemperatureLayer {
+    type Service = TemperatureLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        TemperatureLayerService {
+            inner,
+            temperature: self.temperature,
+        }
+    }
+}
+
+/// A Tower service to add a temperature value to your `CompletionRequestBuilder`.
+/// Not intended to be used directly - use [`TemperatureLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct TemperatureLayerService<S> {
+    inner: S,
+    temperature: f64,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for TemperatureLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let temperature = self.temperature;
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.temperature(temperature))
+        })
+    }
+}
+
+/// A Tower service to add tools to your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct ToolsLayer {
+    tools: Vec<ToolDefinition>,
+}
+
+impl ToolsLayer {
+    pub fn new(tools: Vec<ToolDefinition>) -> Self {
+        Self { tools }
+    }
+}
+
+impl<S> Layer<S> for ToolsLayer {
+    type Service = ToolsLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        ToolsLayerService {
+            inner,
+            tools: self.tools.clone(),
+        }
+    }
+}
+
+/// A Tower service to add tools to your `CompletionRequestBuilder`.
+/// Not intended to be used directly - use [`ToolsLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct ToolsLayerService<S> {
+    inner: S,
+    tools: Vec<ToolDefinition>,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for ToolsLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let tools = self.tools.clone();
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.tools(tools))
+        })
+    }
+}
+
+/// A Tower layer to add a preamble ("system message") to your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct PreambleLayer {
+    preamble: String,
+}
+
+impl PreambleLayer {
+    pub fn new(preamble: String) -> Self {
+        Self { preamble }
+    }
+}
+
+impl<S> Layer<S> for PreambleLayer {
+    type Service = PreambleLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        PreambleLayerService {
+            inner,
+            preamble: self.preamble.clone(),
+        }
+    }
+}
+
+/// A Tower service to add a preamble ("system message") to your `CompletionRequestBuilder`.
+/// Not intended to be used directly - use [`PreambleLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct PreambleLayerService<S> {
+    inner: S,
+    preamble: String,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for PreambleLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let preamble = self.preamble.clone();
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.preamble(preamble))
+        })
+    }
+}
+
+/// A Tower layer to add additional parameters to your `CompletionRequestBuilder` (which are not already covered by the other parameters).
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct AdditionalParamsLayer {
+    additional_params: serde_json::Value,
+}
+
+impl AdditionalParamsLayer {
+    pub fn new(additional_params: serde_json::Value) -> Self {
+        Self { additional_params }
+    }
+}
+
+impl<S> Layer<S> for AdditionalParamsLayer {
+    type Service = AdditionalParamsLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        AdditionalParamsLayerService {
+            inner,
+            additional_params: self.additional_params.clone(),
+        }
+    }
+}
+
+/// A Tower layer to add additional parameters to your `CompletionRequestBuilder` (which are not already covered by the other parameters).
+/// Not intended to be used directly - use [`AdditionalParamsLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct AdditionalParamsLayerService<S> {
+    inner: S,
+    additional_params: serde_json::Value,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for AdditionalParamsLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let additional_params = self.additional_params.clone();
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.additional_params(additional_params))
+        })
+    }
+}
+
+/// A Tower layer to add a maximum tokens parameter to your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct MaxTokensLayer {
+    max_tokens: u64,
+}
+
+impl MaxTokensLayer {
+    pub fn new(max_tokens: u64) -> Self {
+        Self { max_tokens }
+    }
+}
+
+impl<S> Layer<S> for MaxTokensLayer {
+    type Service = MaxTokensLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        MaxTokensLayerService {
+            inner,
+            max_tokens: self.max_tokens,
+        }
+    }
+}
+
+/// A Tower service to add a maximum tokens parameter to your `CompletionRequestBuilder`.
+/// Not intended to be used directly - use [`MaxTokensLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct MaxTokensLayerService<S> {
+    inner: S,
+    max_tokens: u64,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for MaxTokensLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let max_tokens = self.max_tokens;
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.max_tokens(max_tokens))
+        })
+    }
+}
+
+/// A Tower layer to add a chat history to your `CompletionRequestBuilder`.
+/// Intended to be used with [`CompletionRequestBuilderService`].
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct ChatHistoryLayer {
+    chat_history: Vec<Message>,
+}
+
+impl ChatHistoryLayer {
+    pub fn new(chat_history: Vec<Message>) -> Self {
+        Self { chat_history }
+    }
+}
+
+impl<S> Layer<S> for ChatHistoryLayer {
+    type Service = ChatHistoryLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        ChatHistoryLayerService {
+            inner,
+            chat_history: self.chat_history.clone(),
+        }
+    }
+}
+
+/// A Tower service to add a chat history to your `CompletionRequestBuilder`.
+/// Not intended to be used directly - use [`ChatHistoryLayer`] instead.
+///
+/// See [`CompletionRequestBuilderService`] for usage.
+pub struct ChatHistoryLayerService<S> {
+    inner: S,
+    chat_history: Vec<Message>,
+}
+
+impl<M, Msg, S> Service<(M, Msg)> for ChatHistoryLayerService<S>
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+    S: Service<(M, Msg), Response = CompletionRequestBuilder<M>> + Clone + Send + 'static,
+    S::Future: Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: (M, Msg)) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let chat_history = self.chat_history.clone();
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            Ok(res.messages(chat_history))
+        })
+    }
+}
+
+/// A `tower` service for building a completion request.
+/// Note that the last layer to be applied goes first and the core service is placed last (so it gets executedd from bottom to top).
+///
+/// Usage:
+/// ```rust
+/// let agent = rig::providers::openai::Client::from_env();
+/// let model = agent.completion_model("gpt-4o");
+///
+/// let service = tower::ServiceBuilder::new()
+///     .layer(FinishBuilding)
+///     .layer(TemperatureLayer::new(0.0))
+///     .layer(PreambleLayer::new("You are a helpful assistant"))
+///     .service(CompletionRequestBuilderService);
+///
+/// let request = service.call((model, "Hello world!".to_string())).await.unwrap();
+///
+/// let res = request.send().await.unwrap();
+///
+/// println!("{res:?}");
+/// ```
+pub struct CompletionRequestBuilderService;
+
+impl<M, Msg> Service<(M, Msg)> for CompletionRequestBuilderService
+where
+    M: CompletionModel + Send + 'static,
+    Msg: Into<Message> + Send + 'static,
+{
+    type Response = CompletionRequestBuilder<M>;
+    type Error = ();
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, (model, prompt): (M, Msg)) -> Self::Future {
+        Box::pin(async move { Ok(CompletionRequestBuilder::new(model, prompt)) })
+    }
+}
diff --git a/rig-core/src/middlewares/completion.rs b/rig-core/src/middlewares/completion.rs
new file mode 100644
index 0000000..5cfe419
--- /dev/null
+++ b/rig-core/src/middlewares/completion.rs
@@ -0,0 +1,262 @@
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use tower::{Layer, Service};
+
+use crate::{
+    completion::{
+        CompletionError, CompletionModel, CompletionRequest, CompletionRequestBuilder,
+        CompletionResponse, Document, ToolDefinition,
+    },
+    message::{Message, ToolResultContent, UserContent},
+    OneOrMany,
+};
+
+#[derive(Clone)]
+pub struct CompletionLayer<M> {
+    model: M,
+    preamble: Option<String>,
+    documents: Vec<Document>,
+    tools: Vec<ToolDefinition>,
+    temperature: Option<f64>,
+    max_tokens: Option<u64>,
+    additional_params: Option<serde_json::Value>,
+}
+
+impl<M> CompletionLayer<M>
+where
+    M: CompletionModel,
+{
+    pub fn builder(model: M) -> CompletionLayerBuilder<M> {
+        CompletionLayerBuilder::new(model)
+    }
+}
+
+#[derive(Default)]
+pub struct CompletionLayerBuilder<M> {
+    model: M,
+    preamble: Option<String>,
+    documents: Vec<Document>,
+    tools: Vec<ToolDefinition>,
+    temperature: Option<f64>,
+    max_tokens: Option<u64>,
+    additional_params: Option<serde_json::Value>,
+}
+
+impl<M> CompletionLayerBuilder<M>
+where
+    M: CompletionModel,
+{
+    pub fn new(model: M) -> Self {
+        Self {
+            model,
+            preamble: None,
+            documents: vec![],
+            tools: vec![],
+            temperature: None,
+            max_tokens: None,
+            additional_params: None,
+        }
+    }
+
+    pub fn preamble(mut self, preamble: String) -> Self {
+        self.preamble = Some(preamble);
+
+        self
+    }
+
+    pub fn preamble_opt(mut self, preamble: Option<String>) -> Self {
+        self.preamble = preamble;
+
+        self
+    }
+
+    pub fn documents(mut self, documents: Vec<Document>) -> Self {
+        self.documents = documents;
+
+        self
+    }
+
+    pub fn tools(mut self, tools: Vec<ToolDefinition>) -> Self {
+        self.tools = tools;
+
+        self
+    }
+
+    pub fn temperature(mut self, temperature: f64) -> Self {
+        self.temperature = Some(temperature);
+
+        self
+    }
+
+    pub fn temperature_opt(mut self, temperature: Option<f64>) -> Self {
+        self.temperature = temperature;
+
+        self
+    }
+
+    pub fn max_tokens(mut self, max_tokens: u64) -> Self {
+        self.max_tokens = Some(max_tokens);
+
+        self
+    }
+
+    pub fn max_tokens_opt(mut self, max_tokens: Option<u64>) -> Self {
+        self.max_tokens = max_tokens;
+
+        self
+    }
+
+    pub fn additional_params(mut self, params: serde_json::Value) -> Self {
+        self.additional_params = Some(params);
+
+        self
+    }
+
+    pub fn additional_params_opt(mut self, params: Option<serde_json::Value>) -> Self {
+        self.additional_params = params;
+
+        self
+    }
+
+    pub fn build(self) -> CompletionLayer<M> {
+        CompletionLayer {
+            model: self.model,
+            preamble: self.preamble,
+
+            documents: self.documents,
+            tools: self.tools,
+            temperature: self.temperature,
+            max_tokens: self.max_tokens,
+            additional_params: self.additional_params,
+        }
+    }
+}
+
+impl<M, S> Layer<S> for CompletionLayer<M>
+where
+    M: CompletionModel,
+{
+    type Service = CompletionLayerService<M, S>;
+    fn layer(&self, inner: S) -> Self::Service {
+        CompletionLayerService {
+            inner,
+            model: self.model.clone(),
+            preamble: self.preamble.clone(),
+
+            documents: self.documents.clone(),
+            tools: self.tools.clone(),
+            temperature: self.temperature,
+            max_tokens: self.max_tokens,
+            additional_params: self.additional_params.clone(),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct CompletionLayerService<M, S> {
+    inner: S,
+    model: M,
+    preamble: Option<String>,
+    documents: Vec<Document>,
+    tools: Vec<ToolDefinition>,
+    temperature: Option<f64>,
+    max_tokens: Option<u64>,
+    additional_params: Option<serde_json::Value>,
+}
+
+impl<M, S> Service<CompletionRequest> for CompletionLayerService<M, S>
+where
+    M: CompletionModel + 'static,
+    S: Service<CompletionRequest, Response = (Vec<Message>, String, ToolResultContent)>
+        + Clone
+        + Send
+        + 'static,
+    S::Future: Send,
+{
+    type Response = CompletionResponse<M::Response>;
+    type Error = CompletionError;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let model = self.model.clone();
+        let preamble = self.preamble.clone();
+        let documents = self.documents.clone();
+        let temperature = self.temperature;
+        let tools = self.tools.clone();
+        let max_tokens = self.max_tokens;
+        let additional_params = self.additional_params.clone();
+
+        Box::pin(async move {
+            let Ok((messages, id, tool_content)) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            let tool_result_message = Message::User {
+                content: OneOrMany::one(UserContent::tool_result(id, OneOrMany::one(tool_content))),
+            };
+
+            let mut req = CompletionRequestBuilder::new(model.clone(), tool_result_message)
+                .documents(documents.clone())
+                .tools(tools.clone())
+                .messages(messages)
+                .temperature_opt(temperature)
+                .max_tokens_opt(max_tokens)
+                .additional_params_opt(additional_params.clone());
+
+            if let Some(preamble) = preamble.clone() {
+                req = req.preamble(preamble);
+            }
+
+            let req = req.build();
+
+            model.completion(req).await
+        })
+    }
+}
+
+/// A completion model as a Tower service.
+///
+/// This allows you to use an LLM model (or client) essentially anywhere you'd use a regular Tower layer, like in an Axum web service.
+#[derive(Clone)]
+pub struct CompletionService<M> {
+    /// The model itself.
+    model: M,
+}
+
+impl<M> CompletionService<M>
+where
+    M: CompletionModel,
+{
+    pub fn new(model: M) -> Self {
+        Self { model }
+    }
+}
+
+impl<M> Service<CompletionRequest> for CompletionService<M>
+where
+    M: CompletionModel + 'static,
+{
+    type Response = CompletionResponse<M::Response>;
+    type Error = CompletionError;
+
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let model = self.model.clone();
+
+        Box::pin(async move { model.completion(req).await })
+    }
+}
diff --git a/rig-core/src/middlewares/components.rs b/rig-core/src/middlewares/components.rs
new file mode 100644
index 0000000..c8fb3cb
--- /dev/null
+++ b/rig-core/src/middlewares/components.rs
@@ -0,0 +1,247 @@
+use std::{fmt::Debug, future::Future, marker::PhantomData, pin::Pin, task::Poll};
+
+use tower::{Layer, Service};
+
+use crate::{
+    completion::{CompletionRequest, CompletionResponse},
+    message::{AssistantContent, Text},
+};
+
+#[derive(Clone)]
+pub struct AwaitApprovalLayer<T> {
+    integration: T,
+}
+
+impl<T> AwaitApprovalLayer<T>
+where
+    T: HumanInTheLoop + Clone,
+{
+    pub fn new(integration: T) -> Self {
+        Self { integration }
+    }
+
+    pub fn with_predicate<R, D>(self, predicate: R) -> AwaitApprovalLayerWithPredicate<D, R, T>
+    where
+        D: Debug,
+        R: Fn() -> Pin<Box<dyn Future<Output = bool> + Send>> + Clone + Send + 'static,
+    {
+        AwaitApprovalLayerWithPredicate {
+            integration: self.integration,
+            predicate,
+            _t: PhantomData,
+        }
+    }
+}
+
+impl<S, T> Layer<S> for AwaitApprovalLayer<T>
+where
+    T: HumanInTheLoop + Clone,
+{
+    type Service = AwaitApprovalLayerService<S, T>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        AwaitApprovalLayerService::new(inner, self.integration.clone())
+    }
+}
+
+#[derive(Clone)]
+pub struct AwaitApprovalLayerService<S, T> {
+    inner: S,
+    integration: T,
+}
+
+impl<S, T> AwaitApprovalLayerService<S, T>
+where
+    T: HumanInTheLoop,
+{
+    pub fn new(inner: S, integration: T) -> Self {
+        Self { inner, integration }
+    }
+}
+
+impl<S, T, Response> Service<CompletionRequest> for AwaitApprovalLayerService<S, T>
+where
+    S: Service<CompletionRequest, Response = CompletionResponse<Response>> + Clone + Send + 'static,
+    S::Future: Send,
+    Response: Clone + 'static + Send,
+    T: HumanInTheLoop + Clone + Send + 'static,
+{
+    type Response = CompletionResponse<Response>;
+    type Error = bool;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(
+        &mut self,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let await_approval_loop = self.integration.clone();
+
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            let AssistantContent::Text(Text { text }) = res.choice.first() else {
+                todo!("Handle error properly");
+            };
+
+            if await_approval_loop.send_message(&text).await.is_err() {
+                todo!("Handle error properly");
+            }
+
+            let Ok(bool) = await_approval_loop.await_approval().await else {
+                todo!("Handle error properly");
+            };
+
+            if bool {
+                Ok(res)
+            } else {
+                todo!("Handle error properly - we should abort the pipeline here if the user wants to abort");
+            }
+        })
+    }
+}
+
+pub struct AwaitApprovalLayerWithPredicate<P, R, T> {
+    integration: T,
+    predicate: R,
+    _t: PhantomData<P>,
+}
+
+impl<D, R, S, T> Layer<S> for AwaitApprovalLayerWithPredicate<D, R, T>
+where
+    T: HumanInTheLoop + Clone,
+    D: Debug,
+    R: Fn(&D) -> Pin<Box<dyn Future<Output = bool> + Send>> + Clone + Send + 'static,
+{
+    type Service = AwaitApprovalLayerServiceWithPredicate<D, R, S, T>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        let predicate = self.predicate.clone();
+        AwaitApprovalLayerServiceWithPredicate::new(inner, self.integration.clone(), predicate)
+    }
+}
+
+pub struct AwaitApprovalLayerServiceWithPredicate<D, R, S, T> {
+    inner: S,
+    integration: T,
+    predicate: R,
+    _t: PhantomData<D>,
+}
+
+impl<D, R, S, T> AwaitApprovalLayerServiceWithPredicate<D, R, S, T>
+where
+    T: HumanInTheLoop,
+    R: Fn(&D) -> Pin<Box<dyn Future<Output = bool> + Send>> + Clone + Send + 'static,
+    D: Debug,
+{
+    pub fn new(inner: S, integration: T, predicate: R) -> Self {
+        Self {
+            inner,
+            integration,
+            predicate,
+            _t: PhantomData,
+        }
+    }
+}
+
+impl<D, S, T, Response, R> Service<CompletionRequest>
+    for AwaitApprovalLayerServiceWithPredicate<D, R, S, T>
+where
+    R: Fn(&CompletionResponse<Response>) -> Pin<Box<dyn Future<Output = bool> + Send>>
+        + Clone
+        + Send
+        + 'static,
+    S: Service<CompletionRequest, Response = CompletionResponse<Response>> + Clone + Send + 'static,
+    S::Future: Send,
+    Response: Clone + 'static + Send,
+    T: HumanInTheLoop + Clone + Send + 'static,
+{
+    type Response = CompletionResponse<Response>;
+    type Error = bool;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(
+        &mut self,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let await_approval_loop = self.integration.clone();
+        let predicate = self.predicate.clone();
+
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            if predicate(&res).await {
+                return Ok(res);
+            }
+
+            let AssistantContent::Text(Text { text }) = res.choice.first() else {
+                todo!("Handle error properly");
+            };
+
+            if await_approval_loop.send_message(&text).await.is_err() {
+                todo!("Handle error properly");
+            }
+
+            let Ok(bool) = await_approval_loop.await_approval().await else {
+                todo!("Handle error properly");
+            };
+
+            if bool {
+                Ok(res)
+            } else {
+                todo!("Handle error properly - we should abort the pipeline here if the user wants to abort");
+            }
+        })
+    }
+}
+
+pub trait HumanInTheLoop {
+    fn send_message(
+        &self,
+        res: &str,
+    ) -> impl Future<Output = Result<(), Box<dyn std::error::Error>>> + Send;
+    fn await_approval(
+        &self,
+    ) -> impl Future<Output = Result<bool, Box<dyn std::error::Error>>> + Send;
+}
+
+pub struct Stdout;
+
+impl HumanInTheLoop for Stdout {
+    async fn send_message(&self, res: &str) -> Result<(), Box<dyn std::error::Error>> {
+        print!(
+            "Current result: {res}
+
+            Would you like to approve this step? [Y/n]"
+        );
+
+        Ok(())
+    }
+
+    async fn await_approval(&self) -> Result<bool, Box<dyn std::error::Error>> {
+        let mut string = String::new();
+
+        loop {
+            std::io::stdin().read_line(&mut string).unwrap();
+
+            match string.to_lowercase().trim() {
+                "y" | "yes" => break Ok(true),
+                "n" | "no" => break Ok(false),
+                _ => println!("Please respond with 'y' or 'n'."),
+            }
+        }
+    }
+}
diff --git a/rig-core/src/middlewares/extractor.rs b/rig-core/src/middlewares/extractor.rs
new file mode 100644
index 0000000..ddd0a29
--- /dev/null
+++ b/rig-core/src/middlewares/extractor.rs
@@ -0,0 +1,87 @@
+use serde::Deserialize;
+use std::{future::Future, marker::PhantomData, pin::Pin, task::Poll};
+use tower::{Layer, Service};
+
+use crate::{
+    completion::{CompletionRequest, CompletionResponse},
+    message::{AssistantContent, Text},
+};
+
+use super::ServiceError;
+
+#[derive(Clone)]
+pub struct ExtractorLayer<T> {
+    _t: PhantomData<T>,
+}
+
+impl<T> ExtractorLayer<T>
+where
+    T: for<'a> Deserialize<'a>,
+{
+    pub fn new() -> Self {
+        Self { _t: PhantomData }
+    }
+}
+
+impl<T> Default for ExtractorLayer<T>
+where
+    T: for<'a> Deserialize<'a>,
+{
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<S, T> Layer<S> for ExtractorLayer<T>
+where
+    T: for<'a> Deserialize<'a>,
+{
+    type Service = ExtractorLayerService<S, T>;
+    fn layer(&self, inner: S) -> Self::Service {
+        ExtractorLayerService { inner, _t: self._t }
+    }
+}
+
+#[derive(Clone)]
+pub struct ExtractorLayerService<S, T> {
+    inner: S,
+    _t: PhantomData<T>,
+}
+
+impl<S, F, T> Service<CompletionRequest> for ExtractorLayerService<S, T>
+where
+    S: Service<CompletionRequest, Response = CompletionResponse<F>, Error = ServiceError>
+        + Clone
+        + Send
+        + 'static,
+    S::Future: Send,
+    F: 'static,
+    T: for<'a> Deserialize<'a> + 'static,
+{
+    type Response = T;
+    type Error = ServiceError;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(
+        &mut self,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let mut inner = self.inner.clone();
+
+        Box::pin(async move {
+            let res = inner.call(req).await?;
+
+            let AssistantContent::Text(Text { text }) = res.choice.first() else {
+                todo!("Handle errors properly");
+            };
+
+            let obj = serde_json::from_str::<T>(&text)?;
+
+            Ok(obj)
+        })
+    }
+}
diff --git a/rig-core/src/middlewares/mod.rs b/rig-core/src/middlewares/mod.rs
new file mode 100644
index 0000000..53da6ab
--- /dev/null
+++ b/rig-core/src/middlewares/mod.rs
@@ -0,0 +1,39 @@
+use thiserror::Error;
+
+use crate::{
+    completion::CompletionError, extractor::ExtractionError, tool::ToolSetError,
+    vector_store::VectorStoreError,
+};
+
+pub mod build_completions;
+pub mod completion;
+pub mod components;
+pub mod extractor;
+pub mod parallel;
+pub mod rag;
+pub mod tools;
+
+#[derive(Debug, Error)]
+pub enum ServiceError {
+    #[error("{0}")]
+    ExtractionError(#[from] ExtractionError),
+    #[error("{0}")]
+    CompletionError(#[from] CompletionError),
+    #[error("{0}")]
+    ToolSetError(#[from] ToolSetError),
+    #[error("{0}")]
+    VectorStoreError(#[from] VectorStoreError),
+    #[error("Value required but was null: {0}")]
+    RequiredOptionNotFound(String),
+    #[error("{0}")]
+    Json(#[from] serde_json::Error),
+    #[error("Custom error: {0}")]
+    Other(#[from] Box<dyn std::error::Error + Send + Sync>),
+}
+
+impl ServiceError {
+    pub fn required_option_not_exists<S: Into<String>>(val: S) -> Self {
+        let val: String = val.into();
+        Self::RequiredOptionNotFound(val)
+    }
+}
diff --git a/rig-core/src/middlewares/parallel.rs b/rig-core/src/middlewares/parallel.rs
new file mode 100644
index 0000000..1d619be
--- /dev/null
+++ b/rig-core/src/middlewares/parallel.rs
@@ -0,0 +1,88 @@
+use std::{future::Future, pin::Pin};
+
+use tower::Service;
+
+use crate::completion::CompletionRequest;
+
+use super::ServiceError;
+
+pub struct Stackable<A, B> {
+    pub inner: A,
+    pub outer: B,
+}
+
+impl<A, B> Stackable<A, B> {
+    pub fn new(inner: A, outer: B) -> Self {
+        Self { inner, outer }
+    }
+
+    pub fn take_values(self) -> (A, B) {
+        (self.inner, self.outer)
+    }
+}
+
+#[derive(Clone)]
+pub struct ParallelService<S, T> {
+    first_service: S,
+    second_service: T,
+}
+
+impl<S, T> ParallelService<S, T>
+where
+    S: Service<CompletionRequest>,
+    T: Service<CompletionRequest>,
+{
+    pub fn new(first_service: S, second_service: T) -> Self {
+        Self {
+            first_service,
+            second_service,
+        }
+    }
+}
+
+impl<S, T> Service<CompletionRequest> for ParallelService<S, T>
+where
+    S: Service<CompletionRequest, Error = ServiceError> + Clone + Send + 'static,
+    S::Future: Send,
+    S::Response: Send + 'static,
+    T: Service<CompletionRequest, Error = ServiceError> + Clone + Send + 'static,
+    T::Future: Send,
+    T::Response: Send + 'static,
+{
+    type Response = Stackable<S::Response, T::Response>;
+    type Error = ServiceError;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(
+        &mut self,
+        _cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), Self::Error>> {
+        std::task::Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let mut first = self.first_service.clone();
+        let mut second = self.second_service.clone();
+        Box::pin(async move {
+            let res1 = first.call(req.clone()).await?;
+            let res2 = second.call(req.clone()).await?;
+
+            let stackable = Stackable::new(res1, res2);
+
+            Ok(stackable)
+        })
+    }
+}
+
+#[macro_export]
+macro_rules! parallel_service {
+    ($service1:tt, $service2:tt) => {
+        $crate::pipeline::parallel::ParallelService::new($service1, $service2)
+    };
+    ($op1:tt $(, $ops:tt)*) => {
+        $crate::pipeline::parallel::ParallelService::new(
+            $service1,
+            $crate::parallel_op!($($ops),*)
+        )
+    };
+}
diff --git a/rig-core/src/middlewares/rag.rs b/rig-core/src/middlewares/rag.rs
new file mode 100644
index 0000000..5af4f3f
--- /dev/null
+++ b/rig-core/src/middlewares/rag.rs
@@ -0,0 +1,64 @@
+use std::{
+    future::Future,
+    marker::PhantomData,
+    pin::Pin,
+    sync::Arc,
+    task::{Context, Poll},
+};
+
+use serde::{Deserialize, Serialize};
+use tower::Service;
+
+use crate::{completion::CompletionRequest, vector_store::VectorStoreIndex};
+
+use super::ServiceError;
+
+pub struct RagService<V, T> {
+    vector_index: Arc<V>,
+    num_results: usize,
+    _phantom: PhantomData<T>,
+}
+
+impl<V, T> RagService<V, T>
+where
+    V: VectorStoreIndex,
+{
+    pub fn new(vector_index: V, num_results: usize) -> Self {
+        Self {
+            vector_index: Arc::new(vector_index),
+            num_results,
+            _phantom: PhantomData,
+        }
+    }
+}
+
+impl<V, T> Service<CompletionRequest> for RagService<V, T>
+where
+    V: VectorStoreIndex + 'static,
+    T: Serialize + for<'a> Deserialize<'a> + Send,
+{
+    type Response = RagResult<T>;
+    type Error = ServiceError;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let vector_index = self.vector_index.clone();
+        let num_results = self.num_results;
+
+        Box::pin(async move {
+            let Some(prompt) = req.prompt.rag_text() else {
+                return Err(ServiceError::required_option_not_exists("rag_text"));
+            };
+
+            let res = vector_index.top_n(&prompt, num_results).await?;
+
+            Ok(res)
+        })
+    }
+}
+
+pub type RagResult<T> = Vec<(f64, String, T)>;
diff --git a/rig-core/src/middlewares/tools.rs b/rig-core/src/middlewares/tools.rs
new file mode 100644
index 0000000..09c9404
--- /dev/null
+++ b/rig-core/src/middlewares/tools.rs
@@ -0,0 +1,86 @@
+use crate::{
+    completion::{CompletionRequest, CompletionResponse},
+    message::{AssistantContent, Message, ToolResultContent},
+    tool::{ToolSet, ToolSetError},
+    OneOrMany,
+};
+use std::{future::Future, pin::Pin, sync::Arc, task::Poll};
+
+use tower::{Layer, Service};
+
+#[derive(Clone)]
+pub struct ToolLayer {
+    tools: Arc<ToolSet>,
+}
+
+impl ToolLayer {
+    pub fn new(tools: ToolSet) -> Self {
+        Self {
+            tools: Arc::new(tools),
+        }
+    }
+}
+
+impl<S> Layer<S> for ToolLayer {
+    type Service = ToolLayerService<S>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        ToolLayerService {
+            inner,
+            tools: Arc::clone(&self.tools),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct ToolLayerService<S> {
+    inner: S,
+    tools: Arc<ToolSet>,
+}
+
+impl<S, T> Service<CompletionRequest> for ToolLayerService<S>
+where
+    S: Service<CompletionRequest, Response = CompletionResponse<T>> + Clone + Send + 'static,
+    T: Send + 'static,
+    S::Future: Send,
+{
+    type Response = (Vec<Message>, String, ToolResultContent);
+    type Error = ToolSetError;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn poll_ready(&mut self, _cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: CompletionRequest) -> Self::Future {
+        let mut inner = self.inner.clone();
+        let tools = self.tools.clone();
+        let mut messages = req.chat_history.clone();
+
+        Box::pin(async move {
+            let Ok(res) = inner.call(req).await else {
+                todo!("Handle error properly");
+            };
+
+            let AssistantContent::ToolCall(tool_call) = res.choice.first() else {
+                todo!("Handle error properly");
+            };
+
+            messages.push(Message::Assistant {
+                content: OneOrMany::one(AssistantContent::ToolCall(tool_call.clone())),
+            });
+
+            let Ok(res) = tools
+                .call(
+                    &tool_call.function.name,
+                    tool_call.function.arguments.to_string(),
+                )
+                .await
+            else {
+                todo!("Implement proper error handling");
+            };
+
+            Ok((messages, tool_call.id, ToolResultContent::text(res)))
+        })
+    }
+}