Blazing fast, structured, leveled logging in Go.

go get -u go.uber.org/zap

In contexts where performance is nice, but not critical, use the SugaredLogger. It's 4-10x faster than than other structured logging libraries and includes both structured and printf-style APIs.

logger, _ := NewProduction()
sugar := logger.Sugar()
sugar.Infow("Failed to fetch URL.",
  // Structured context as loosely-typed key-value pairs.
  "url", url,
  "attempt", retryNum,
  "backoff", time.Second,
)
sugar.Infof("Failed to fetch URL: %s", url)

When performance and type safety are critical, use the Logger. It's even faster than the SugaredLogger and allocates far less, but it only supports structured logging.

logger, _ := NewProduction()
logger.Info("Failed to fetch URL.",
  // Structured context as strongly-typed Field values.
  zap.String("url", url),
  zap.Int("attempt", tryNum),
  zap.Duration("backoff", time.Second),
)

For applications that log in the hot path, reflection-based serialization and string formatting are prohibitively expensive — they're CPU-intensive and make many small allocations. Put differently, using encoding/json and fmt.Fprintf to log tons of interface{}s makes your application slow.

Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely-typed API.

As measured by its own benchmarking suite, not only is zap more performant than comparable structured logging libraries — it's also faster than the standard library. Like all benchmarks, take these with a grain of salt.¹

Log a message and 10 fields:

Log a message with a logger that already has 10 fields of context:

Log a static string, without any context or printf-style templating:

The current release is v1.0.0-rc.2. No further breaking changes are planned unless wider use reveals critical bugs or usability issues, but users who need absolute stability should wait for the 1.0.0 release.

¹ In particular, keep in mind that we may be benchmarking against slightly older versions of other libraries. Versions are pinned in zap's glide.lock file. ↩