Programming language: Go

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:zap: zap GoDoc Build Status Coverage Status

Blazing fast, structured, leveled logging in Go.


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](FAQ.md) for more details.


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: zap 862 ns/op +0% 5 allocs/op
:zap: zap (sugared) 1250 ns/op +45% 11 allocs/op
zerolog 4021 ns/op +366% 76 allocs/op
go-kit 4542 ns/op +427% 105 allocs/op
apex/log 26785 ns/op +3007% 115 allocs/op
logrus 29501 ns/op +3322% 125 allocs/op
log15 29906 ns/op +3369% 122 allocs/op

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

Package Time Time % to zap Objects Allocated
:zap: zap 126 ns/op +0% 0 allocs/op
:zap: zap (sugared) 187 ns/op +48% 2 allocs/op
zerolog 88 ns/op -30% 0 allocs/op
go-kit 5087 ns/op +3937% 103 allocs/op
log15 18548 ns/op +14621% 73 allocs/op
apex/log 26012 ns/op +20544% 104 allocs/op
logrus 27236 ns/op +21516% 113 allocs/op

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

Package Time Time % to zap Objects Allocated
:zap: zap 118 ns/op +0% 0 allocs/op
:zap: zap (sugared) 191 ns/op +62% 2 allocs/op
zerolog 93 ns/op -21% 0 allocs/op
go-kit 280 ns/op +137% 11 allocs/op
standard library 499 ns/op +323% 2 allocs/op
apex/log 1990 ns/op +1586% 10 allocs/op
logrus 3129 ns/op +2552% 24 allocs/op
log15 3887 ns/op +3194% 23 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.


We encourage and support an active, healthy community of contributors — including you! Details are in the [contribution guide](CONTRIBUTING.md) and the [code of conduct](CODE_OF_CONDUCT.md). 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](LICENSE.txt).

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

*Note that all licence references and agreements mentioned in the zap README section above are relevant to that project's source code only.