diff --git a/tests/tools/test_ssh_environment.py b/tests/tools/test_ssh_environment.py
new file mode 100644
index 0000000000..aca8b22592
--- /dev/null
+++ b/tests/tools/test_ssh_environment.py
@@ -0,0 +1,39 @@
+import pytest
+
+from tools.environments import ssh as ssh_env
+
+
+def test_ensure_ssh_available_raises_clear_error_when_missing(monkeypatch):
+    monkeypatch.setattr(ssh_env.shutil, "which", lambda _name: None)
+
+    with pytest.raises(RuntimeError, match="SSH is not installed or not in PATH"):
+        ssh_env._ensure_ssh_available()
+
+
+def test_ssh_environment_checks_availability_before_connect(monkeypatch):
+    monkeypatch.setattr(ssh_env.shutil, "which", lambda _name: None)
+    monkeypatch.setattr(
+        ssh_env.SSHEnvironment,
+        "_establish_connection",
+        lambda self: pytest.fail("_establish_connection should not run when ssh is missing"),
+    )
+
+    with pytest.raises(RuntimeError, match="openssh-client"):
+        ssh_env.SSHEnvironment(host="example.com", user="alice")
+
+
+def test_ssh_environment_connects_when_ssh_exists(monkeypatch):
+    called = {"count": 0}
+
+    monkeypatch.setattr(ssh_env.shutil, "which", lambda _name: "/usr/bin/ssh")
+
+    def _fake_establish(self):
+        called["count"] += 1
+
+    monkeypatch.setattr(ssh_env.SSHEnvironment, "_establish_connection", _fake_establish)
+
+    env = ssh_env.SSHEnvironment(host="example.com", user="alice")
+
+    assert called["count"] == 1
+    assert env.host == "example.com"
+    assert env.user == "alice"
diff --git a/tools/environments/ssh.py b/tools/environments/ssh.py
index 83cc335b1e..3a9095cf88 100644
--- a/tools/environments/ssh.py
+++ b/tools/environments/ssh.py
@@ -1,6 +1,7 @@
 """SSH remote execution environment with ControlMaster connection persistence."""
 
 import logging
+import shutil
 import subprocess
 import tempfile
 import threading
@@ -13,6 +14,14 @@ from tools.interrupt import is_interrupted
 logger = logging.getLogger(__name__)
 
 
+def _ensure_ssh_available() -> None:
+    """Fail fast with a clear error when the SSH client is unavailable."""
+    if not shutil.which("ssh"):
+        raise RuntimeError(
+            "SSH is not installed or not in PATH. Install OpenSSH client: apt install openssh-client"
+        )
+
+
 class SSHEnvironment(BaseEnvironment):
     """Run commands on a remote machine over SSH.
 
@@ -35,6 +44,7 @@ class SSHEnvironment(BaseEnvironment):
         self.control_dir = Path(tempfile.gettempdir()) / "hermes-ssh"
         self.control_dir.mkdir(parents=True, exist_ok=True)
         self.control_socket = self.control_dir / f"{user}@{host}:{port}.sock"
+        _ensure_ssh_available()
         self._establish_connection()
 
     def _build_ssh_command(self, extra_args: list = None) -> list: