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

logger, _ := zap.NewProduction()
defer logger.Sync() // flushes buffer, if any
sugar := logger.Sugar()
sugar.Infow("failed to fetch URL",
  // Structured context as loosely typed key-value pairs.
  "url", url,
  "attempt", 3,
  "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, _ := zap.NewProduction()
defer logger.Sync()
logger.Info("failed to fetch URL",
  // Structured context as strongly typed Field values.
  zap.String("url", url),
  zap.Int("attempt", 3),
  zap.Duration("backoff", time.Second),
)

See the documentation and FAQ for more details.

Performance

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 packages — 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:

Package	Time	Time % to zap	Objects Allocated
⚡ zap	2900 ns/op	+0%	5 allocs/op
⚡ zap (sugared)	3475 ns/op	+20%	10 allocs/op
zerolog	10639 ns/op	+267%	32 allocs/op
go-kit	14434 ns/op	+398%	59 allocs/op
logrus	17104 ns/op	+490%	81 allocs/op
apex/log	32424 ns/op	+1018%	66 allocs/op
log15	33579 ns/op	+1058%	76 allocs/op

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

Package	Time	Time % to zap	Objects Allocated
⚡ zap	373 ns/op	+0%	0 allocs/op
⚡ zap (sugared)	452 ns/op	+21%	1 allocs/op
zerolog	288 ns/op	-23%	0 allocs/op
go-kit	11785 ns/op	+3060%	58 allocs/op
logrus	19629 ns/op	+5162%	70 allocs/op
log15	21866 ns/op	+5762%	72 allocs/op
apex/log	30890 ns/op	+8182%	55 allocs/op

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

Package	Time	Time % to zap	Objects Allocated
⚡ zap	381 ns/op	+0%	0 allocs/op
⚡ zap (sugared)	410 ns/op	+8%	1 allocs/op
zerolog	369 ns/op	-3%	0 allocs/op
standard library	385 ns/op	+1%	2 allocs/op
go-kit	606 ns/op	+59%	11 allocs/op
logrus	1730 ns/op	+354%	25 allocs/op
apex/log	1998 ns/op	+424%	7 allocs/op
log15	4546 ns/op	+1093%	22 allocs/op

Development Status: Stable

All APIs are finalized, and no breaking changes will be made in the 1.x series of releases. Users of semver-aware dependency management systems should pin zap to ^1.

Contributing

We encourage and support an active, healthy community of contributors — including you! Details are in the contribution guide and the code of conduct. The zap maintainers keep an eye on issues and pull requests, but you can also report any negative conduct to oss-conduct@uber.com. That email list is a private, safe space; even the zap maintainers don't have access, so don't hesitate to hold us to a high standard.

Released under the MIT License.

¹ In particular, keep in mind that we may be benchmarking against slightly older versions of other packages. Versions are pinned in the benchmarks/go.mod file. ↩