Cockatrice ships with a "diagnostics mode" that prints detailed debug messages about what the client is doing. This is extremely useful when asking for help, because it shows exactly what happened: which URL the card picture loader tried, whether it found or missed a file on disk, whether a download succeeded or failed, which redirects were followed, and much more. Each of these messages belongs to a category, and you can enable or disable categories individually.

Don't worry, this sounds more technical than it is. You only need to do two things: create one small text file, and tell Cockatrice where it is. There are no installation steps and you can undo everything later (see When you are done).

Step 1: Create the file

Open a plain text editor (Notepad on Windows, TextEdit on macOS, or any text editor on Linux) and paste the following content:

[Rules]
# The default log level is info
*.debug = false
 
# Turn on debug level logs for the card picture loader and all its sub categories
card_picture_loader.* = true

Save the file with the exact name qtlogging.ini in a place you can find again, for example your Documents folder.

Attention: The file name matters: it must be qtlogging.ini, not qtlogging.ini.txt. If your text editor adds a .txt extension automatically, you need to stop it from doing so (see below). On macOS, TextEdit must be switched to plain text mode first via 'Format → Make Plain Text'.

The file contains one rule per line. The *.debug = false rule turns off debug messages everywhere by default, and the card_picture_loader.* = true line then re-enables them for the card picture loader. The .* at the end means "this category and all of its sub categories". To enable a different category instead, just replace that line with the category name of your choice, for example card_database.loading = true or window_main.startup = true.

Step 2: Tell Cockatrice where the file is

Cockatrice does not know about the file yet. You have to point it there by setting an environment variable called QT_LOGGING_CONF to the full location of your file. How to do this depends on your operating system:

Windows

Press the Windows key, type "environment variables", and open "Edit the system environment variables".
Click "Environment Variables...", then under "User variables" click "New...".
Set "Variable name" to QT_LOGGING_CONF and "Variable value" to the full path of your file, for example C:\Users\YourName\Documents\qtlogging.ini.
Confirm all dialogs, then close and reopen Cockatrice.

Alternatively, if Cockatrice is installed in a folder you can write to, you can simply place the qtlogging.ini file directly next to the Cockatrice executable (in the same folder as cockatrice.exe) and skip the environment variable altogether. Note that this copy may be replaced when you update the client.

macOS

Open the Terminal app (it is in 'Applications → Utilities') and run the following two commands, replacing the path with the full location of your file:

launchctl setenv QT_LOGGING_CONF /path/to/qtlogging.ini

open -a Cockatrice

You can also use export QT_LOGGING_CONF=/path/to/qtlogging.ini to set the variable for the current terminal session.

The setting stays active until you log out or restart your Mac. If you have multiple users on the same Mac, be aware that this setting only applies to your user account.

Linux

For a quick test, open a terminal and start Cockatrice with the file on the command line, replacing the path with the full location of your file:

QT_LOGGING_CONF=/path/to/qtlogging.ini cockatrice

If this works and you want it to apply every time you start Cockatrice, add the following line to your ~/.profile file and log in again:

export QT_LOGGING_CONF="/path/to/qtlogging.ini"

Step 3: See the logs

Now that debug logging is enabled, open Cockatrice and trigger the behavior you are investigating, for example by opening a deck, reloading the card database, or starting a game.

The easiest way to see the logs is to use the built-in log viewer inside Cockatrice itself: open 'Help → View Debug Log'. A window appears that shows the log messages live and keeps the most recent entries. It even has a 'Copy to clipboard' button so you can paste the output into a bug report or a Discord message. This works the same on every operating system.

If you prefer to capture everything to a file instead, start Cockatrice with the --debug-output option:

cockatrice --debug-output

Cockatrice then writes the full log to a file called qdebug.txt in the folder it was started from.

Which categories are available?

Every message Cockatrice logs belongs to a category. The following table lists the most useful ones for troubleshooting, grouped by area. Enable a category by adding a line like category = true to your qtlogging.ini file (or use a .* suffix, e.g. card_picture_loader.*, to include all sub categories).

What you want to see	Categories
Card picture loading (URLs, local file hits/misses, downloads, redirects)	card_picture_loader.*
Card database loading and parsing	card_database, card_database.loading, card_database.loading.success_or_failure, cockatrice_xml.*
Card, set, and deck information	card_info, card_list, deck_loader
Startup sequence and update checks	window_main.startup.*, release_channel, spoiler_background_updater
User interface and themes	theme_manager, sound_engine, flow_layout, flow_widget.*, pixel_map_generator, card_info_picture_widget
Networking and servers	local_client, remote_client, tapped_out_interface, servers_settings
In-game logic	player, game_scene., card_zone., view_zone, game_event_handler
Dialogs and tabs	dlg_settings, dlg_update, dlg_tip_of_the_day, tab_game, tab_message, tab_supervisor
Settings and shortcuts	settings_cache, shortcuts_settings
Deck and card filtering	filter_string, deck_filter_string, syntax_help

For example, to investigate why a card database update seems to fail, enable the card database categories:

[Rules]
*.debug = false
 
card_database = true
card_database.loading = true
card_database.loading.success_or_failure = true
cockatrice_xml.* = true

When you are done

To turn the diagnostics back off, just reverse what you did: remove the QT_LOGGING_CONF environment variable (or unset it again via launchctl unsetenv QT_LOGGING_CONF on macOS) and/or delete the qtlogging.ini file, then restart Cockatrice. Leaving it on is harmless, but the extra logging can make the client slightly slower.

For the full details on how Cockatrice logging works, including the complete list of categories, see Logging.