Metadata

ID: csharp-best-practices/logger-constant-template

Language: C#

Severity: Info

Category: Best Practices

Description

Using interpolated strings ($"...") or string concatenation forces the CLR to build a new string every time the log statement executes — even if the current log level is disabled (e.g., when logging at Debug in production). Prefer using constant templates when logging data.

Non-Compliant Code Examples

_logger.LogInformation("User " + userId + " logged in");

_logger.LogInformation($"User {userId} logged in at {timestamp}");

Compliant Code Examples

// check log enablement before
if (_logger.IsEnabled(LogLevel.Debug)) {
    _logger.LogInformation("User " + userId + " logged in");
}

_logger.LogInformation("User {UserId} logged in at {Timestamp}", userId, timestamp);