Logging Levels in Go

LogInfo ✅

• The message describes expected, routine, or successful operations.
• You’re providing context or breadcrumbs for debugging later.
• The message is not indicative of a problem, but may still be useful for understanding flow or state.

log.Info("User successfully logged in")
log.Info("Started background job for report generation")
log.Info("Connected to database")

LogWarn ⚠️

• Something unexpected happened, but the app can continue running.
• It may not be critical now, but could cause issues down the line.
• You’re highlighting a potential risk, degraded performance, or a fallback being used.

log.Warn("Failed to fetch user profile image; using default avatar")
log.Warn("Cache miss for key: session_123")
log.Warn("Third-party API responded slowly")

LogInfo vs. LogWarn - Rule of Thumb

Use Warn if you or another developer would want to be aware of the situation during routine monitoring or debugging, because it might signal a problem or inefficiency.

Use Info for useful milestones or routine operational insight.

LogError ❌

• An operation failed and it shouldn’t have.
• The issue prevents correct execution or requires manual attention.
• You are handling the error (e.g. catching it and not crashing the program), but it’s still a real problem.
• It signals a bug, data issue, or infrastructure problem.

log.Error("Failed to connect to database", zap.Error(err))
log.Error("Unable to save user preferences", zap.String("user_id", id), zap.Error(err))
log.Error("Unexpected panic in request handler", zap.Any("request", req), zap.Error(err))

Summary of logging levels