feat(logging): add setup_logging with LOG_LEVEL support

src/grist_mcp/logging.py

@@ -1,8 +1,31 @@
 """Logging configuration and utilities."""
 
+import logging
+import os
 from datetime import datetime
 
 
+def setup_logging() -> None:
+    """Configure logging based on LOG_LEVEL environment variable.
+
+    Valid levels: DEBUG, INFO, WARNING, ERROR (default: INFO)
+    """
+    level_name = os.environ.get("LOG_LEVEL", "INFO").upper()
+    level = getattr(logging, level_name, None)
+
+    if not isinstance(level, int):
+        level = logging.INFO
+
+    logger = logging.getLogger("grist_mcp")
+    logger.setLevel(level)
+
+    # Only add handler if not already configured
+    if not logger.handlers:
+        handler = logging.StreamHandler()
+        handler.setFormatter(logging.Formatter("%(message)s"))
+        logger.addHandler(handler)
+
+
 def extract_stats(tool_name: str, arguments: dict, result: dict) -> str:
     """Extract meaningful stats from tool call based on tool type."""
     if tool_name == "list_documents":

tests/unit/test_logging.py

@@ -1,5 +1,7 @@
 """Unit tests for logging module."""
 
+import logging
+
 from grist_mcp.logging import truncate_token, extract_stats, format_tool_log
 
 
@@ -119,3 +121,32 @@ class TestFormatToolLog:
         )
         assert "error" in line
         assert "\n    Grist API error: Invalid column 'foo'" in line
+
+
+class TestSetupLogging:
+    def test_default_level_is_info(self, monkeypatch):
+        monkeypatch.delenv("LOG_LEVEL", raising=False)
+
+        from grist_mcp.logging import setup_logging
+        setup_logging()
+
+        logger = logging.getLogger("grist_mcp")
+        assert logger.level == logging.INFO
+
+    def test_respects_log_level_env(self, monkeypatch):
+        monkeypatch.setenv("LOG_LEVEL", "DEBUG")
+
+        from grist_mcp.logging import setup_logging
+        setup_logging()
+
+        logger = logging.getLogger("grist_mcp")
+        assert logger.level == logging.DEBUG
+
+    def test_invalid_level_defaults_to_info(self, monkeypatch):
+        monkeypatch.setenv("LOG_LEVEL", "INVALID")
+
+        from grist_mcp.logging import setup_logging
+        setup_logging()
+
+        logger = logging.getLogger("grist_mcp")
+        assert logger.level == logging.INFO