diff --git a/src/specify_cli/_console.py b/src/specify_cli/_console.py
index 33bd70f77f..8d1216387f 100644
--- a/src/specify_cli/_console.py
+++ b/src/specify_cli/_console.py
@@ -34,6 +34,10 @@
 
 console = Console(highlight=False)
 
+# Stderr-bound console for error/diagnostic output, so human-facing messages
+# never contaminate stdout (which carries machine-readable ``--json`` payloads).
+err_console = Console(stderr=True, highlight=False)
+
 class StepTracker:
     """Track and render hierarchical steps without emojis, similar to Claude Code tree output.
     Supports live auto-refresh via an attached refresh callback.
diff --git a/src/specify_cli/commands/bundle/__init__.py b/src/specify_cli/commands/bundle/__init__.py
index 185e00acf6..afae9bcf84 100644
--- a/src/specify_cli/commands/bundle/__init__.py
+++ b/src/specify_cli/commands/bundle/__init__.py
@@ -13,7 +13,7 @@
 
 import typer
 
-from ..._console import console
+from ..._console import console, err_console
 from ...bundler import BundlerError
 from ...bundler.lib.project import (
     active_integration,
@@ -41,7 +41,9 @@
 
 def _fail(message: str) -> None:
     """Print an actionable error to stderr and exit non-zero."""
-    console.print(f"[red]Error:[/red] {message}", style=None)
+    # Use the stderr console so the error never lands on stdout, which under
+    # ``--json`` carries the machine-readable payload and must stay parseable.
+    err_console.print(f"[red]Error:[/red] {message}", style=None)
     raise typer.Exit(code=1)
 
 
diff --git a/tests/contract/test_bundle_cli.py b/tests/contract/test_bundle_cli.py
index 018b2bbec1..58a26fae91 100644
--- a/tests/contract/test_bundle_cli.py
+++ b/tests/contract/test_bundle_cli.py
@@ -62,6 +62,21 @@ def test_commands_outside_project_fail_with_guidance(tmp_path: Path, monkeypatch
     assert "Spec Kit project" in result.output
 
 
+def test_fail_writes_error_to_stderr_not_stdout(capsys):
+    """_fail must write to stderr, not stdout: every bundle command routes errors
+    through it, and under --json the error would otherwise corrupt the JSON payload
+    that consumers read from stdout."""
+    import typer
+
+    from specify_cli.commands.bundle import _fail
+
+    with pytest.raises(typer.Exit):
+        _fail("something broke")
+    captured = capsys.readouterr()
+    assert "something broke" in captured.err
+    assert "something broke" not in captured.out
+
+
 def test_search_works_without_a_project(tmp_path: Path, monkeypatch):
     # Discovery commands fall back to the built-in/user catalog stack and must
     # not require a Spec Kit project (matches README/quickstart examples).