diff --git a/src/agent_env/cli/__init__.py b/src/agent_env/cli/__init__.py
index e39688d4..aad88a4a 100644
--- a/src/agent_env/cli/__init__.py
+++ b/src/agent_env/cli/__init__.py
@@ -1,4 +1,6 @@
 import logging
+from collections.abc import Iterator
+from contextlib import contextmanager
 
 import click
 
@@ -43,14 +45,32 @@ def invoke(self, ctx: click.Context):
             raise click.ClickException("\n".join([str(e), *getattr(e, "__notes__", ())])) from e
 
 
+@contextmanager
+def _verbose_logging() -> Iterator[None]:
+    """Log agent-env's own DEBUG messages, and only warnings from other libraries, while a command runs: their debug
+    logs can carry credentials, as hpack's do, which log every HTTP/2 header Modal's client sends, its token among
+    them. The loggers' levels are put back after it, so a CLI invoked in-process leaves the caller's logging as it was."""
+    logging.basicConfig(level=logging.WARNING, format="%(asctime)s %(name)s %(message)s")
+    loggers = [logging.getLogger(name) for name in ("agent_env", "agentenv_protocol")]
+    levels = [logger.level for logger in loggers]
+    for logger in loggers:
+        logger.setLevel(logging.DEBUG)
+    try:
+        yield
+    finally:
+        for logger, level in zip(loggers, levels):
+            logger.setLevel(level)
+
+
 @click.group(cls=_UserErrorsAreNotCrashes)
 @click.version_option(package_name="agentenv-framework", prog_name="agent-env", message="%(prog)s %(version)s")
-@click.option("--verbose", "-v", is_flag=True, help="Enable verbose logging (DEBUG level)")
+@click.option("--verbose", "-v", is_flag=True,
+              help="Enable agent-env's DEBUG logging (other libraries log warnings only)")
 @click.pass_context
 def cli(ctx: click.Context, verbose: bool):
     """Agent environment CLI."""
     if verbose:
-        logging.basicConfig(level=logging.DEBUG, format="%(asctime)s %(name)s %(message)s")
+        ctx.with_resource(_verbose_logging())
     # For this command only, so a CLI invoked in-process leaves the caller's stores as they were.
     ctx.with_resource(namespace_routing())
 
diff --git a/tst/unit/cli/verbose_logging_test.py b/tst/unit/cli/verbose_logging_test.py
new file mode 100644
index 00000000..d7b4b3b1
--- /dev/null
+++ b/tst/unit/cli/verbose_logging_test.py
@@ -0,0 +1,41 @@
+"""``agent-env -v`` logs agent-env's own DEBUG messages, and only warnings from other libraries, whose debug logs can
+carry credentials: hpack logs every HTTP/2 header Modal's client sends, its token among them."""
+
+import logging
+import subprocess
+import sys
+
+from click.testing import CliRunner
+
+from agent_env.cli import cli
+
+# In a fresh interpreter, as the CLI runs: pytest's own handlers on the root logger would make basicConfig a no-op here.
+_LOGS = """
+import logging
+from agent_env.cli import _verbose_logging
+with _verbose_logging():
+    logging.getLogger("agent_env.providers.sandbox_providers.modal_sandbox").debug("creating a sandbox")
+    logging.getLogger("agentenv_protocol.client").debug("reading a card")
+    logging.getLogger("hpack.hpack").debug("Adding b'x-modal-token-secret'=b'as-0000' to the header table")
+    logging.getLogger("hpack.hpack").warning("a header table warning")
+"""
+
+
+def test_verbose_logs_agent_envs_debug_messages_and_only_warnings_from_other_libraries():
+    done = subprocess.run([sys.executable, "-c", _LOGS], capture_output=True, text=True, timeout=120)
+
+    assert done.returncode == 0, done.stderr
+    assert "creating a sandbox" in done.stderr and "reading a card" in done.stderr
+    assert "a header table warning" in done.stderr
+    assert "x-modal-token-secret" not in done.stderr
+
+
+def test_a_verbose_command_run_in_process_leaves_the_callers_logging_as_it_was():
+    """Run in a caller's process, as the tests and any embedding code run it, -v lasts only for its command."""
+    loggers = [logging.getLogger(name) for name in ("agent_env", "agentenv_protocol")]
+    before = [logger.level for logger in loggers]
+
+    result = CliRunner().invoke(cli, ["-v", "config", "--help"])
+
+    assert result.exit_code == 0, result.output
+    assert [logger.level for logger in loggers] == before