diff --git a/router/src/lib.rs b/router/src/lib.rs
index 1c06eb8a..67a14d5c 100644
--- a/router/src/lib.rs
+++ b/router/src/lib.rs
@@ -520,6 +520,46 @@ pub(crate) struct ChatRequest {
     #[serde(default)]
     #[schema(nullable = true, example = 0.95)]
     pub top_p: Option<f32>,
+
+    /// A list of tools the model may call. Currently, only functions are supported as a tool. Use this to provide a list of
+    /// functions the model may generate JSON inputs for.
+    #[serde(default)]
+    #[schema(nullable = true, example = "null")]
+    pub tools: Option<Vec<Tool>>,
+}
+
+// TODO: define and use better types for tools
+
+// #[derive(Clone, Debug, Deserialize, Serialize, ToSchema)]
+// enum ToolType {
+//     #[serde(rename = "function")]
+//     Function,
+// }
+
+// impl Default for ToolType {
+//     fn default() -> Self {
+//         ToolType::Function
+//     }
+// }
+
+// #[derive(Clone, Debug, Deserialize, Serialize, ToSchema)]
+// pub(crate) struct Function {
+//     pub description: String,
+//     pub name: String,
+//     #[serde(
+//         rename = "json",
+//         deserialize_with = "json_object_or_string_to_string::deserialize"
+//     )]
+//     pub parameters: String,
+// }
+
+#[derive(Clone, Debug, Deserialize, Serialize, ToSchema)]
+pub(crate) struct Tool {
+    // The type of the tool. Currently, only 'function' is supported.
+    #[schema(example = "function")]
+    pub r#type: String,
+    // Grab the tool as generic JSON for debugging purposes.
+    pub function: serde_json::Value,
 }
 
 #[derive(Clone, Serialize, Deserialize)]
diff --git a/router/src/server.rs b/router/src/server.rs
index 9fdd66cc..8f40ee2a 100644
--- a/router/src/server.rs
+++ b/router/src/server.rs
@@ -580,8 +580,47 @@ async fn chat_completions(
     let logprobs = req.logprobs.unwrap_or(false);
     let seed = req.seed;
 
+    // Build a new JSON schema that defines the "$functions" object
+    // and requires the grammar to choose anyOf the functions defined.
+    let mut tools = serde_json::json!({});
+
+    // First decompose the tools and use the function name as the key
+    // and the parameters as the value in the "$functions" object.
+    if let Some(req_tools) = &req.tools {
+        for tool in req_tools {
+            let func = tool.function.clone();
+            let name = func.get("name").unwrap().as_str().unwrap();
+            let parameters = func.get("parameters").unwrap().as_object().unwrap().clone();
+            // add a entry to the "$functions" object
+            tools["$functions"][name] = serde_json::Value::Object(parameters);
+        }
+
+        // now add the properties to the root object
+        tools["properties"]["function"]["anyOf"] = serde_json::Value::Array(
+            req.tools
+                .as_ref()
+                .unwrap()
+                .iter()
+                // map each tool to a $ref to the function
+                .map(|tool| {
+                    let func = tool.function.clone();
+                    let name = func.get("name").unwrap().as_str().unwrap();
+                    serde_json::json!({
+                        "$ref": format!("#/$functions/{}", name)
+                    })
+                })
+                .collect(),
+        );
+    }
+
+    // only add grammar if tools are present
+    let grammar = match req.tools {
+        Some(_grammar) => Some(crate::GrammarType::Json(tools.to_string())),
+        None => None,
+    };
+
     // apply chat template to flatten the request into a single input
-    let inputs = match infer.apply_chat_template(req.messages) {
+    let mut inputs = match infer.apply_chat_template(req.messages) {
         Ok(inputs) => inputs,
         Err(err) => {
             metrics::increment_counter!("tgi_request_failure", "err" => "validation");
@@ -596,6 +635,11 @@ async fn chat_completions(
         }
     };
 
+    // append the tools to the inputs with TOOL prompt
+    let tool_prompt =
+        "Based on the conversation, please choose the most appropriate tool to use:".to_string();
+    inputs = format!("{inputs}\n\n{tool_prompt}\n\n{tools}\n\n");
+
     // build the request passing some parameters
     let generate_request = GenerateRequest {
         inputs: inputs.to_string(),
@@ -617,7 +661,7 @@ async fn chat_completions(
             decoder_input_details: !stream,
             seed,
             top_n_tokens: None,
-            grammar: None,
+            grammar,
         },
     };
 
diff --git a/server/text_generation_server/utils/logits_process.py b/server/text_generation_server/utils/logits_process.py
index 40f31ce2..c9a32ff7 100644
--- a/server/text_generation_server/utils/logits_process.py
+++ b/server/text_generation_server/utils/logits_process.py
@@ -513,6 +513,9 @@ class GrammarLogitProcessor(LogitsProcessor):
         start_time = time.time()
         if grammar_type == GrammarType.GRAMMAR_TYPE_JSON:
             schema = build_regex_from_object(schema)
+        elif grammar_type == GrammarType.OPTIONAL_GRAMMAR_TYPE_REGEX:
+            # TODO: use a better method to handle optional grammars
+            schema = f"({build_regex_from_object(schema)})|.*"
         elif grammar_type == GrammarType.GRAMMAR_TYPE_REGEX:
             pass  # schema is already a regex just here for clarity
         fsm = RegexFSM(schema, tokenizer)