zap

Installation

go get -u go.uber.org/zap

Note that zap only supports the two most recent minor versions of Go.

Quick Start

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	656 ns/op	+0%	5 allocs/op
zap (sugared)	935 ns/op	+43%	10 allocs/op
zerolog	380 ns/op	-42%	1 allocs/op
go-kit	2249 ns/op	+243%	57 allocs/op
slog (LogAttrs)	2479 ns/op	+278%	40 allocs/op
slog	2481 ns/op	+278%	42 allocs/op
apex/log	9591 ns/op	+1362%	63 allocs/op
log15	11393 ns/op	+1637%	75 allocs/op
logrus	11654 ns/op	+1677%	79 allocs/op

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

Package	Time	Time % to zap	Objects Allocated
zap	67 ns/op	+0%	0 allocs/op
zap (sugared)	84 ns/op	+25%	1 allocs/op
zerolog	35 ns/op	-48%	0 allocs/op
slog	193 ns/op	+188%	0 allocs/op
slog (LogAttrs)	200 ns/op	+199%	0 allocs/op
go-kit	2460 ns/op	+3572%	56 allocs/op
log15	9038 ns/op	+13390%	70 allocs/op
apex/log	9068 ns/op	+13434%	53 allocs/op
logrus	10521 ns/op	+15603%	68 allocs/op

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

Package	Time	Time % to zap	Objects Allocated
zap	63 ns/op	+0%	0 allocs/op
zap (sugared)	81 ns/op	+29%	1 allocs/op
zerolog	32 ns/op	-49%	0 allocs/op
standard library	124 ns/op	+97%	1 allocs/op
slog	196 ns/op	+211%	0 allocs/op
slog (LogAttrs)	200 ns/op	+217%	0 allocs/op
go-kit	213 ns/op	+238%	9 allocs/op
apex/log	771 ns/op	+1124%	5 allocs/op
logrus	1439 ns/op	+2184%	23 allocs/op
log15	2069 ns/op	+3184%	20 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. ↩