Configuring Logging

Logging

The Strands SDK provides logging infrastructure to give visibility into its operations.

=== "Python"

Strands SDK uses Python's standard [`logging`](https://docs.python.org/3/library/logging.html) module. The SDK implements a straightforward logging approach:

1. **Module-level Loggers**: Each module creates its own logger using `logging.getLogger(__name__)`, following Python best practices for hierarchical logging.

2. **Root Logger**: All loggers are children of the "strands" root logger, making it easy to configure logging for the entire SDK.

3. **Default Behavior**: By default, the SDK doesn't configure any handlers or log levels, allowing you to integrate it with your application's logging configuration.

=== "TypeScript"

Strands SDK provides a simple logging infrastructure with a global logger that can be configured to use your preferred logging implementation.

1. **Logger Interface**: A simple interface (`debug`, `info`, `warn`, `error`) compatible with popular logging libraries like Pino, Winston, and the browser/Node.js console.

2. **Global Logger**: A single global logger instance configured via `configureLogging()`.

3. **Default Behavior**: By default, the SDK only logs warnings and errors to the console. Debug and info logs are no-ops unless you configure a custom logger.

Configuring Logging

=== "Python"

To enable logging for the Strands Agents SDK, you can configure the "strands" logger:

```python
import logging

# Configure the root strands logger
logging.getLogger("strands").setLevel(logging.DEBUG)

# Add a handler to see the logs
logging.basicConfig(
    format="%(levelname)s | %(name)s | %(message)s",
    handlers=[logging.StreamHandler()]
)
```

=== "TypeScript"

To enable logging for the Strands Agents SDK, use the `configureLogging` function. The SDK's logger interface is compatible with standard console and popular logging libraries.

**Using console:**

```typescript
--8<-- "user-guide/observability-evaluation/logs.ts:basic_console"
```

**Using Pino:**

```typescript
--8<-- "user-guide/observability-evaluation/logs.ts:pino_setup"
```

**Default Behavior:**

- By default, the SDK only logs warnings and errors using `console.warn()` and `console.error()`
- Debug and info logs are no-ops by default (zero performance overhead)
- Configure a custom logger with appropriate log levels to enable debug/info logging

Log Levels

The Strands Agents SDK uses standard log levels:

• DEBUG: Detailed operational information for troubleshooting. Extensively used for tool registration, discovery, configuration, and execution flows.

• INFO: General informational messages. Currently not used.

• WARNING: Potential issues that don't prevent operation, such as validation failures, specification errors, and compatibility warnings.

• ERROR: Significant problems that prevent specific operations from completing successfully, such as execution failures and handler errors.

• CRITICAL: Reserved for catastrophic failures.

Key Logging Areas

=== "Python"

The Strands Agents SDK logs information in several key areas. Let's look at what kinds of logs you might see when using the following example agent with a calculator tool:

```python
from strands import Agent
from strands_tools import calculator

# Create an agent with the calculator tool
agent = Agent(tools=[calculator])
result = agent("What is 125 * 37?")
```

When running this code with logging enabled, you'll see logs from different components of the SDK as the agent processes the request, calls the calculator tool, and generates a response.

### Tool Registry and Execution

Logs related to tool discovery, registration, and execution:

```
# Tool registration
DEBUG | strands.tools.registry | tool_name=<calculator> | registering tool
DEBUG | strands.tools.registry | tool_name=<calculator>, tool_type=<function>, is_dynamic=<False> | registering tool
DEBUG | strands.tools.registry | tool_name=<calculator> | loaded tool config
DEBUG | strands.tools.registry | tool_count=<1> | tools configured

# Tool discovery
DEBUG | strands.tools.registry | tools_dir=</path/to/tools> | found tools directory
DEBUG | strands.tools.registry | tools_dir=</path/to/tools> | scanning
DEBUG | strands.tools.registry | tool_modules=<['calculator', 'weather']> | discovered

# Tool validation
WARNING | strands.tools.registry | tool_name=<invalid_tool> | spec validation failed | Missing required fields in tool spec: description
DEBUG | strands.tools.registry | tool_name=<calculator> | loaded dynamic tool config

# Tool execution
DEBUG | strands.event_loop.event_loop | tool_use=<calculator_tool_use_id> | streaming

# Tool hot reloading
DEBUG | strands.tools.registry | tool_name=<calculator> | searching directories for tool
DEBUG | strands.tools.registry | tool_name=<calculator> | reloading tool
DEBUG | strands.tools.registry | tool_name=<calculator> | successfully reloaded tool
```

### Event Loop

Logs related to the event loop processing:

```
ERROR | strands.event_loop.error_handler | an exception occurred in event_loop_cycle | ContextWindowOverflowException
DEBUG | strands.event_loop.error_handler | message_index=<5> | found message with tool results at index
```

### Model Interactions

Logs related to interactions with foundation models:

```
DEBUG | strands.models.bedrock | config=<{'model_id': 'us.anthropic.claude-4-sonnet-20250219-v1:0'}> | initializing
WARNING | strands.models.bedrock | bedrock threw context window overflow error
DEBUG | strands.models.bedrock | Found blocked output guardrail. Redacting output.
```

=== "TypeScript"

The TypeScript SDK currently has minimal logging, primarily focused on model interactions. Logs are generated for:

- **Model configuration warnings**: Unsupported features (e.g., cache points in OpenAI, guard content)
- **Model response warnings**: Invalid formats, unexpected data structures
- **Bedrock-specific operations**: Configuration auto-detection, unsupported event types

Example logs you might see:

```
# Model configuration warnings
WARN cache points are not supported in openai system prompts, ignoring cache points
WARN guard content is not supported in openai system prompts, removing guard content block

# Model response warnings
WARN choice=<null> | invalid choice format in openai chunk
WARN tool_call=<{"type":"function","id":"xyz"}> | received tool call with invalid index

# Bedrock-specific logs
DEBUG model_id=<us.anthropic.claude-sonnet-4-20250514-v1:0>, include_tool_result_status=<true> | auto-detected includeToolResultStatus
WARN block_key=<unknown_key> | skipping unsupported block key
WARN event_type=<unknown_type> | unsupported bedrock event type
```

Future versions will include more detailed logging for tool operations and event loop processing.

Advanced Configuration

=== "Python"

### Filtering Specific Modules

You can configure logging for specific modules within the SDK:

```python
import logging

# Enable DEBUG logs for the tool registry only
logging.getLogger("strands.tools.registry").setLevel(logging.DEBUG)

# Set WARNING level for model interactions
logging.getLogger("strands.models").setLevel(logging.WARNING)
```

### Custom Handlers

You can add custom handlers to process logs in different ways:

```python
import logging
import json

class JsonFormatter(logging.Formatter):
    def format(self, record):
        log_data = {
            "timestamp": self.formatTime(record),
            "level": record.levelname,
            "name": record.name,
            "message": record.getMessage()
        }
        return json.dumps(log_data)

# Create a file handler with JSON formatting
file_handler = logging.FileHandler("strands_agents_sdk.log")
file_handler.setFormatter(JsonFormatter())

# Add the handler to the strands logger
logging.getLogger("strands").addHandler(file_handler)
```

=== "TypeScript"

### Custom Logger Implementation

You can implement your own logger to integrate with your application's logging system:

```typescript
--8<-- "user-guide/observability-evaluation/logs.ts:custom_logger"
```

Best Practices

=== "Python"

1. **Configure Early**: Set up logging configuration before initializing the agent
2. **Appropriate Levels**: Use INFO for normal operation and DEBUG for troubleshooting
3. **Structured Log Format**: Use the structured log format shown in examples for better parsing
4. **Performance**: Be mindful of logging overhead in production environments
5. **Integration**: Integrate Strands Agents SDK logging with your application's logging system

=== "TypeScript"

1. **Configure Early**: Call `configureLogging()` before creating any Agent instances
2. **Default Behavior**: By default, only warnings and errors are logged - configure a custom logger to see debug information
3. **Production Performance**: Debug and info logs are no-ops by default, minimizing performance impact
4. **Compatible Libraries**: Use established logging libraries like Pino or Winston for production deployments
5. **Consistent Format**: Ensure your custom logger maintains consistent formatting across log levels