diff --git a/tests/agent/test_redact.py b/tests/agent/test_redact.py
new file mode 100644
index 000000000..52e015ca9
--- /dev/null
+++ b/tests/agent/test_redact.py
@@ -0,0 +1,173 @@
+"""Tests for agent.redact -- secret masking in logs and output."""
+
+import logging
+
+import pytest
+
+from agent.redact import redact_sensitive_text, RedactingFormatter
+
+
+class TestKnownPrefixes:
+    def test_openai_sk_key(self):
+        text = "Using key sk-proj-abc123def456ghi789jkl012"
+        result = redact_sensitive_text(text)
+        assert "sk-pro" in result
+        assert "abc123def456" not in result
+        assert "..." in result
+
+    def test_openrouter_sk_key(self):
+        text = "OPENROUTER_API_KEY=sk-or-v1-abcdefghijklmnopqrstuvwxyz1234567890"
+        result = redact_sensitive_text(text)
+        assert "abcdefghijklmnop" not in result
+
+    def test_github_pat_classic(self):
+        result = redact_sensitive_text("token: ghp_abc123def456ghi789jkl")
+        assert "abc123def456" not in result
+
+    def test_github_pat_fine_grained(self):
+        result = redact_sensitive_text("github_pat_abc123def456ghi789jklmno")
+        assert "abc123def456" not in result
+
+    def test_slack_token(self):
+        token = "xoxb-" + "0" * 12 + "-" + "a" * 14
+        result = redact_sensitive_text(token)
+        assert "a" * 14 not in result
+
+    def test_google_api_key(self):
+        result = redact_sensitive_text("AIzaSyB-abc123def456ghi789jklmno012345")
+        assert "abc123def456" not in result
+
+    def test_perplexity_key(self):
+        result = redact_sensitive_text("pplx-abcdef123456789012345")
+        assert "abcdef12345" not in result
+
+    def test_fal_key(self):
+        result = redact_sensitive_text("fal_abc123def456ghi789jkl")
+        assert "abc123def456" not in result
+
+    def test_short_token_fully_masked(self):
+        result = redact_sensitive_text("key=sk-short1234567")
+        assert "***" in result
+
+
+class TestEnvAssignments:
+    def test_export_api_key(self):
+        text = "export OPENAI_API_KEY=sk-proj-abc123def456ghi789jkl012"
+        result = redact_sensitive_text(text)
+        assert "OPENAI_API_KEY=" in result
+        assert "abc123def456" not in result
+
+    def test_quoted_value(self):
+        text = 'MY_SECRET_TOKEN="supersecretvalue123456789"'
+        result = redact_sensitive_text(text)
+        assert "MY_SECRET_TOKEN=" in result
+        assert "supersecretvalue" not in result
+
+    def test_non_secret_env_unchanged(self):
+        text = "HOME=/home/user"
+        result = redact_sensitive_text(text)
+        assert result == text
+
+    def test_path_unchanged(self):
+        text = "PATH=/usr/local/bin:/usr/bin"
+        result = redact_sensitive_text(text)
+        assert result == text
+
+
+class TestJsonFields:
+    def test_json_api_key(self):
+        text = '{"apiKey": "sk-proj-abc123def456ghi789jkl012"}'
+        result = redact_sensitive_text(text)
+        assert "abc123def456" not in result
+
+    def test_json_token(self):
+        text = '{"access_token": "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.longtoken.here"}'
+        result = redact_sensitive_text(text)
+        assert "eyJhbGciOiJSUzI1NiIs" not in result
+
+    def test_json_non_secret_unchanged(self):
+        text = '{"name": "John", "model": "gpt-4"}'
+        result = redact_sensitive_text(text)
+        assert result == text
+
+
+class TestAuthHeaders:
+    def test_bearer_token(self):
+        text = "Authorization: Bearer sk-proj-abc123def456ghi789jkl012"
+        result = redact_sensitive_text(text)
+        assert "Authorization: Bearer" in result
+        assert "abc123def456" not in result
+
+    def test_case_insensitive(self):
+        text = "authorization: bearer mytoken123456789012345678"
+        result = redact_sensitive_text(text)
+        assert "mytoken12345" not in result
+
+
+class TestTelegramTokens:
+    def test_bot_token(self):
+        text = "bot123456789:ABCDEfghij-KLMNopqrst_UVWXyz12345"
+        result = redact_sensitive_text(text)
+        assert "ABCDEfghij" not in result
+        assert "123456789:***" in result
+
+    def test_raw_token(self):
+        text = "12345678901:ABCDEfghijKLMNopqrstUVWXyz1234567890"
+        result = redact_sensitive_text(text)
+        assert "ABCDEfghij" not in result
+
+
+class TestPassthrough:
+    def test_empty_string(self):
+        assert redact_sensitive_text("") == ""
+
+    def test_none_returns_none(self):
+        assert redact_sensitive_text(None) is None
+
+    def test_normal_text_unchanged(self):
+        text = "Hello world, this is a normal log message with no secrets."
+        assert redact_sensitive_text(text) == text
+
+    def test_code_unchanged(self):
+        text = "def main():\n    print('hello')\n    return 42"
+        assert redact_sensitive_text(text) == text
+
+    def test_url_without_key_unchanged(self):
+        text = "Connecting to https://api.openai.com/v1/chat/completions"
+        assert redact_sensitive_text(text) == text
+
+
+class TestRedactingFormatter:
+    def test_formats_and_redacts(self):
+        formatter = RedactingFormatter("%(message)s")
+        record = logging.LogRecord(
+            name="test", level=logging.INFO, pathname="", lineno=0,
+            msg="Key is sk-proj-abc123def456ghi789jkl012",
+            args=(), exc_info=None,
+        )
+        result = formatter.format(record)
+        assert "abc123def456" not in result
+        assert "sk-pro" in result
+
+
+class TestPrintenvSimulation:
+    """Simulate what happens when the agent runs `env` or `printenv`."""
+
+    def test_full_env_dump(self):
+        env_dump = """HOME=/home/user
+PATH=/usr/local/bin:/usr/bin
+OPENAI_API_KEY=sk-proj-abc123def456ghi789jkl012mno345
+OPENROUTER_API_KEY=sk-or-v1-reallyLongSecretKeyValue12345678
+FIRECRAWL_API_KEY=fc-shortkey123456789012
+TELEGRAM_BOT_TOKEN=bot987654321:ABCDEfghij-KLMNopqrst_UVWXyz12345
+SHELL=/bin/bash
+USER=teknium"""
+        result = redact_sensitive_text(env_dump)
+        # Secrets should be masked
+        assert "abc123def456" not in result
+        assert "reallyLongSecretKey" not in result
+        assert "ABCDEfghij" not in result
+        # Non-secrets should survive
+        assert "HOME=/home/user" in result
+        assert "SHELL=/bin/bash" in result
+        assert "USER=teknium" in result
diff --git a/tools/terminal_tool.py b/tools/terminal_tool.py
index cb0d9cd4e..f758768eb 100644
--- a/tools/terminal_tool.py
+++ b/tools/terminal_tool.py
@@ -1037,8 +1037,12 @@ def terminal_tool(
                 )
                 output = output[:head_chars] + truncated_notice + output[-tail_chars:]
 
+            # Redact secrets from command output (catches env/printenv leaking keys)
+            from agent.redact import redact_sensitive_text
+            output = redact_sensitive_text(output.strip()) if output else ""
+
             return json.dumps({
-                "output": output.strip() if output else "",
+                "output": output,
                 "exit_code": returncode,
                 "error": None
             }, ensure_ascii=False)