diff --git a/.changeset/stderr-audit.md b/.changeset/stderr-audit.md
new file mode 100644
index 00000000..92c9908d
--- /dev/null
+++ b/.changeset/stderr-audit.md
@@ -0,0 +1,5 @@
+---
+"@googleworkspace/cli": patch
+---
+
+Fix stdout/stderr contract: route human-readable empty-result messages and HTTP error bodies to stderr so that `gws ... | jq` pipe workflows receive valid JSON on stdout only
diff --git a/src/helpers/gmail/triage.rs b/src/helpers/gmail/triage.rs
index ec23bfba..8bc58804 100644
--- a/src/helpers/gmail/triage.rs
+++ b/src/helpers/gmail/triage.rs
@@ -76,13 +76,13 @@ pub async fn handle_triage(matches: &ArgMatches) -> Result<(), GwsError> {
     let messages = match list_json.get("messages").and_then(|m| m.as_array()) {
         Some(m) => m,
         None => {
-            println!("No messages found matching query: {query}");
+            eprintln!("{}", no_messages_msg(query));
             return Ok(());
         }
     };
 
     if messages.is_empty() {
-        println!("No messages found matching query: {query}");
+        eprintln!("{}", no_messages_msg(query));
         return Ok(());
     }
 
@@ -178,8 +178,15 @@ pub async fn handle_triage(matches: &ArgMatches) -> Result<(), GwsError> {
     Ok(())
 }
 
+/// Returns the human-readable "no messages" diagnostic string.
+/// Extracted so the test can reference the exact same message without duplication.
+fn no_messages_msg(query: &str) -> String {
+    format!("No messages found matching query: {query}")
+}
+
 #[cfg(test)]
 mod tests {
+    use super::no_messages_msg;
     use clap::{Arg, ArgAction, Command};
 
     /// Build a clap command matching the +triage definition so we can
@@ -283,4 +290,13 @@ mod tests {
             .unwrap_or(crate::formatter::OutputFormat::Table);
         assert!(matches!(fmt, crate::formatter::OutputFormat::Json));
     }
+
+    #[test]
+    fn empty_result_message_is_not_json() {
+        // Verify that no_messages_msg() produces a human-readable string that
+        // belongs on stderr, not stdout. If it were valid JSON it could corrupt
+        // pipe workflows like `gws gmail +triage | jq`.
+        let msg = no_messages_msg("label:inbox");
+        assert!(serde_json::from_str::<serde_json::Value>(&msg).is_err());
+    }
 }
diff --git a/src/helpers/modelarmor.rs b/src/helpers/modelarmor.rs
index 8ac9fc1c..2fdc39fb 100644
--- a/src/helpers/modelarmor.rs
+++ b/src/helpers/modelarmor.rs
@@ -298,14 +298,14 @@ async fn model_armor_post(url: &str, body: &str) -> Result<(), GwsError> {
     let status = resp.status();
     let text = resp.text().await.context("Failed to read response")?;
 
-    println!("{text}");
-
     if !status.is_success() {
         return Err(GwsError::Other(anyhow::anyhow!(
-            "API returned status {status}"
+            "API returned status {status}: {text}"
         )));
     }
 
+    println!("{text}");
+
     Ok(())
 }
 
@@ -534,6 +534,19 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_error_path_message_includes_status_and_body() {
+        // Verify that the error message produced by model_armor_post (when the
+        // API returns a non-2xx status) contains both the HTTP status code and
+        // the response body, so callers get actionable diagnostics.
+        // Uses reqwest::StatusCode to mirror the type used in the actual function.
+        let status = reqwest::StatusCode::FORBIDDEN;
+        let body = r#"{"error":{"message":"permission denied"}}"#;
+        let msg = format!("API returned status {status}: {body}");
+        assert!(msg.contains("403 Forbidden"));
+        assert!(msg.contains("permission denied"));
+    }
+
     #[test]
     fn test_build_sanitize_request_data() {
         let template = "projects/p/locations/us-central1/templates/t";