logcat

Logcat is a command-line tool and system logging facility used in the Android operating system to capture a real-time stream of log messages from the kernel, the Android runtime, and applications. It collects messages from multiple logging buffers and makes them available for viewing, filtering, and analysis by developers during app development and debugging.

The Android logging system organizes messages into buffers such as main, system, radio, events, and crash. Logcat can be used on a device or through the Android Debug Bridge (ADB). In Android Studio, logcat is integrated as a viewing pane that can filter and format output.

Output lines typically include a timestamp, process and thread identifiers, a log priority level, a tag, and the message. The standard log levels are Verbose, Debug, Info, Warn, Error, and Fatal/Assert, with Verbose being the most detailed.

Common usage includes running adb logcat to stream all messages, and applying filters such as -s to show only messages for a given tag or -p to filter by priority. Other options control output format (-v), file redirection (-f), rotation (-r and -n), and clearing buffers (-c).

Because log data can contain sensitive information, access should be controlled. Logcat is a core tool for debugging on Android devices and in development environments, and is complemented by IDE integrations, log viewers, and automated logging workflows.