Log Levels

Log Levels

Six severity levels, ordered from most verbose to most severe. Plus None, used only to switch logging off.

Level	Numeric	Text tag	Icon	Use it for…
Trace	0	TRACE	⬜	The most fine-grained diagnostic detail — method entry/exit, loop values. Normally off in production (noisy/expensive).
Debug	1	DEBUG	🟦	Developer-facing diagnostics — cache hits/misses, internal state, chosen code paths. Usually off in production.
Information	2	INFO	🟩	Normal application flow and business milestones — "started", "user signed in", "job done". The default minimum level.
Warning	3	WARN	🟨	Something unexpected, but the app recovered — a retry, a fallback, a deprecated path, nearing a limit.
Error	4	ERROR	🟥	The current operation failed — typically a caught exception. The app keeps running.
Critical	5	CRITICAL	🟪	The app or a major subsystem is unusable — out of memory, failed startup, data loss. The "wake someone up" level.
None	6	—	—	Not a real entry. Set as the minimum level to disable all logging.

Calling them

Every level has two overloads — a message (with optional template values) and an exception variant:

Log.Trace("Entered {method}", nameof(Process));
Log.Debug("Cache miss for {key}", key);
Log.Information("User {userId} signed in", userId);
Log.Warning("Retry {attempt} of {max}", attempt, max);
Log.Error("Request to {url} failed", url);
Log.Error(ex, "Request to {url} failed", url);     // with exception
Log.Critical(ex, "Unrecoverable startup failure");

The same methods exist on Log<T> (with plain-string messages — see Log vs Log<T>).

Filtering by minimum level

The configured minimum level is the primary volume control: any entry below it is dropped before any formatting work happens, so suppressed logs are cheap.

Log.Configure(o => o.SetMinimumLevel(LogLevel.Warning));

Log.Information("ignored");   // below minimum → dropped
Log.Warning("kept");          // at/above minimum → written

Because the levels are ordered (Trace = 0 … Critical = 5), "minimum level Warning" means Warning, Error, and Critical are written; Trace, Debug, Information are dropped.

Change it at runtime any time:

Log.MinimumLevel = LogLevel.Debug;

Turning logging off

Log.MinimumLevel = LogLevel.None;   // nothing is ever written

Since None (6) is higher than every real level, nothing clears the bar.

Choosing the right level (quick guide)

• Is the app/process dead or about to be? → Critical
• Did this operation fail (exception, request rejected)? → Error
• Did something odd happen but we coped? → Warning
• Is this the normal story of what the app is doing? → Information
• Is this only useful while debugging? → Debug
• Is this trace-level firehose detail? → Trace