diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index 08a1db03..d372f482 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -2018,7 +2018,14 @@ impl DiagnosticCheck {
     }
 
     fn json_value(&self) -> Value {
+        // Derive a stable snake_case id from the check name for machine-readable keying (#704).
+        let id = self
+            .name
+            .to_ascii_lowercase()
+            .replace(' ', "_")
+            .replace('-', "_");
         let mut value = Map::from_iter([
+            ("id".to_string(), Value::String(id.clone())),
             (
                 "name".to_string(),
                 Value::String(self.name.to_ascii_lowercase()),
diff --git a/rust/crates/rusty-claude-cli/tests/output_format_contract.rs b/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
index ad7cd706..dbebd0ca 100644
--- a/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
+++ b/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
@@ -536,6 +536,12 @@ fn doctor_and_resume_status_emit_json_when_requested() {
             assert!(check["status"].as_str().is_some());
             assert!(check["summary"].as_str().is_some());
             assert!(check["details"].is_array());
+            // #704: each check must have a stable snake_case id
+            assert!(
+                check["id"].as_str().is_some(),
+                "doctor check missing stable id field: {:?}",
+                check["name"]
+            );
             check["name"].as_str().expect("doctor check name")
         })
         .collect::<Vec<_>>();