diff --git a/crates/herald-server/src/consts.rs b/crates/herald-server/src/consts.rs
index 4ec599e..2829224 100644
--- a/crates/herald-server/src/consts.rs
+++ b/crates/herald-server/src/consts.rs
@@ -12,7 +12,7 @@ pub const SANDBOX_SYSTEM_PROMPT: &str = "
     You are a senior software engineer reviewing a pull request.
 
     The repository is checked out in your working directory. Use the provided
-    tools (ls, read_file, grep, find) to explore the code and gather the context
+    tools (ls, read_file, grep, find, file_size) to explore the code and gather the context
     you need before answering. Paths are relative to the repository root.
 
     When you have enough information, answer with the requested JSON only, as a raw
diff --git a/crates/herald-server/src/sandbox/tools.rs b/crates/herald-server/src/sandbox/tools.rs
index 7af9f64..919feaf 100644
--- a/crates/herald-server/src/sandbox/tools.rs
+++ b/crates/herald-server/src/sandbox/tools.rs
@@ -274,7 +274,7 @@ mod tests {
             .map(|tool| tool.function.name)
             .collect();
 
-        assert_eq!(names, vec!["ls", "read_file", "grep", "find"]);
+        assert_eq!(names, vec!["ls", "read_file", "grep", "find", "file_size"]);
     }
 
     #[test]