diff --git a/src/format.hpp b/src/format.hpp
index ace8d93..5a50c63 100644
--- a/src/format.hpp
+++ b/src/format.hpp
@@ -79,6 +79,8 @@
  * - **Simple concatenation**: Basic string + number + string combinations
  * - **Compile-time optimization**: When all types/values known at compile time
  * - **Template contexts**: Where compile-time buffer sizing is beneficial
+ * - **IMPORTANT**: Only works with compile-time string literals, NOT runtime
+ * const char*
  *
  * ## Optimization Details:
  * The function uses `ArenaAllocator::allocate_remaining_space()` to claim all
@@ -206,10 +208,12 @@ inline constexpr DoubleTerm term(double s) { return DoubleTerm(s); }
  * optimized term writers for maximum speed.
  *
  * ## Supported Types:
- * - **String literals**: C-style string literals and arrays
+ * - **String literals**: C-style string literals and arrays ("Hello", "World")
  * - **Integers**: All integral types (int, int64_t, uint32_t, etc.)
  * - **Floating point**: double (uses high-precision Grisu2 algorithm)
  * - **Custom types**: Via specialization of `detail::term()`
+ * - **NOT supported**: const char* variables, std::string, std::string_view
+ * variables
  *
  * ## Performance Characteristics:
  * - **Compile-time buffer sizing**: Buffer size calculated at compile time (no
@@ -245,16 +249,23 @@ inline constexpr DoubleTerm term(double s) { return DoubleTerm(s); }
  *
  * ## When to Use:
  * - **Hot paths**: Performance-critical code where formatting speed matters
- * - **Known types**: When argument types are known at compile time
+ * - **Compile-time string literals**: All string arguments must be string
+ * literals (e.g., "Hello")
  * - **Simple formatting**: Concatenation and basic type conversion
  * - **Template code**: Where compile-time optimization is beneficial
+ * - **CANNOT use runtime strings**: No const char*, std::string, or string_view
+ * variables
  *
  * ## When to Use format() Instead:
  * - **Printf-style formatting**: When you need format specifiers like "%d",
  * "%.2f"
- * - **Runtime flexibility**: When format strings come from variables/config
- * - **Complex formatting**: When you need padding, precision, etc.
- * - **Convenience**: For quick debugging or non-critical paths
+ * - **Runtime strings**: When you have const char*, std::string, or string_view
+ * variables
+ * - **Dynamic content**: When format strings come from variables/config/user
+ * input
+ * - **Complex formatting**: When you need padding, precision, width specifiers
+ * - **Mixed literal/runtime**: When combining string literals with runtime
+ * string data
  *
  * @note All arguments are passed by forwarding reference for optimal
  * performance
diff --git a/src/http_handler.cpp b/src/http_handler.cpp
index 0c1d85e..2425ae2 100644
--- a/src/http_handler.cpp
+++ b/src/http_handler.cpp
@@ -195,8 +195,9 @@ void HttpHandler::handlePostCommit(Connection &conn,
     const char *error = state.commit_parser
                             ? state.commit_parser->get_parse_error()
                             : "No parser initialized";
-    std::string error_msg = "Parse failed: ";
-    error_msg += error ? error : "Unknown error";
+    ArenaAllocator &arena = conn.get_arena();
+    std::string_view error_msg =
+        format(arena, "Parse failed: %s", error ? error : "Unknown error");
     send_error_response(conn, 400, error_msg, state.connection_close);
     return;
   }
@@ -319,57 +320,47 @@ void HttpHandler::handleNotFound(Connection &conn,
 void HttpHandler::sendResponse(Connection &conn, int status_code,
                                std::string_view content_type,
                                std::string_view body, bool close_connection) {
-  [[maybe_unused]] ArenaAllocator &arena = conn.get_arena();
-
-  // Build HTTP response using arena
-  std::string response;
-  response.reserve(256 + body.size());
-
-  response += "HTTP/1.1 ";
-  response += std::to_string(status_code);
-  response += " ";
-
-  // Status text
-  switch (status_code) {
-  case 200:
-    response += "OK";
-    break;
-  case 400:
-    response += "Bad Request";
-    break;
-  case 404:
-    response += "Not Found";
-    break;
-  case 500:
-    response += "Internal Server Error";
-    break;
-  default:
-    response += "Unknown";
-    break;
-  }
-
+  ArenaAllocator &arena = conn.get_arena();
   auto *state = static_cast<HttpConnectionState *>(conn.user_data);
 
-  response += "\r\n";
-  response += "Content-Type: ";
-  response += content_type;
-  response += "\r\n";
-  response += "Content-Length: ";
-  response += std::to_string(body.size());
-  response += "\r\n";
-  response += "X-Response-ID: ";
-  response += std::to_string(state->request_id);
-  response += "\r\n";
-
-  if (close_connection) {
-    response += "Connection: close\r\n";
-    conn.close_after_send(); // Signal connection should be closed after sending
-  } else {
-    response += "Connection: keep-alive\r\n";
+  // Status text
+  std::string_view status_text;
+  switch (status_code) {
+  case 200:
+    status_text = "OK";
+    break;
+  case 400:
+    status_text = "Bad Request";
+    break;
+  case 404:
+    status_text = "Not Found";
+    break;
+  case 500:
+    status_text = "Internal Server Error";
+    break;
+  default:
+    status_text = "Unknown";
+    break;
   }
 
-  response += "\r\n";
-  response += body;
+  const char *connection_header = close_connection ? "close" : "keep-alive";
+
+  std::string_view response =
+      format(arena,
+             "HTTP/1.1 %d %.*s\r\n"
+             "Content-Type: %.*s\r\n"
+             "Content-Length: %zu\r\n"
+             "X-Response-ID: %ld\r\n"
+             "Connection: %s\r\n"
+             "\r\n%.*s",
+             status_code, static_cast<int>(status_text.size()),
+             status_text.data(), static_cast<int>(content_type.size()),
+             content_type.data(), body.size(), state->request_id,
+             connection_header, static_cast<int>(body.size()), body.data());
+
+  if (close_connection) {
+    conn.close_after_send();
+  }
 
   conn.append_message(response);
 }
@@ -383,11 +374,11 @@ void HttpHandler::send_json_response(Connection &conn, int status_code,
 void HttpHandler::send_error_response(Connection &conn, int status_code,
                                       std::string_view message,
                                       bool close_connection) {
-  [[maybe_unused]] ArenaAllocator &arena = conn.get_arena();
+  ArenaAllocator &arena = conn.get_arena();
 
-  std::string json = R"({"error":")";
-  json += message;
-  json += R"("})";
+  std::string_view json =
+      format(arena, R"({"error":"%.*s"})", static_cast<int>(message.size()),
+             message.data());
 
   send_json_response(conn, status_code, json, close_connection);
 }
diff --git a/style.md b/style.md
index 689ab94..1ad375f 100644
--- a/style.md
+++ b/style.md
@@ -102,6 +102,27 @@ auto addr = reinterpret_cast<uintptr_t>(ptr);         // Pointer to integer conv
 - **String views** with `std::string_view` to minimize unnecessary copying
 - **Arena allocation** for efficient memory management (~1ns vs ~20-270ns for malloc)
 
+### String Formatting
+- **Always use `format.hpp` functions** - formats directly into arena-allocated memory
+- **Use `static_format()` for performance-sensitive code** - faster but less flexible than `format()`
+- **Use `format()` function with arena allocator** for printf-style formatting
+```cpp
+// Most performance-sensitive - compile-time optimized concatenation
+std::string_view response = static_format(arena,
+    "HTTP/1.1 ", status_code, " OK\r\n",
+    "Content-Length: ", body.size(), "\r\n",
+    "\r\n", body);
+
+// Printf-style formatting - runtime flexible
+ArenaAllocator& arena = conn.get_arena();
+std::string_view response = format(arena,
+    "HTTP/1.1 %d OK\r\n"
+    "Content-Length: %zu\r\n"
+    "\r\n%.*s",
+    status_code, body.size(),
+    static_cast<int>(body.size()), body.data());
+```
+
 ### Complexity Control
 - **Encapsulation is the main tool for controlling complexity**
 - **Header files define the interface** - they are the contract with users of your code