1# :zap: zap [![GoDoc][doc-img]][doc] [![Build Status][ci-img]][ci] [![Coverage Status][cov-img]][cov] 2 3Blazing fast, structured, leveled logging in Go. 4 5## Installation 6 7`go get -u go.uber.org/zap` 8 9Note that zap only supports the two most recent minor versions of Go. 10 11## Quick Start 12 13In contexts where performance is nice, but not critical, use the 14`SugaredLogger`. It's 4-10x faster than other structured logging 15packages and includes both structured and `printf`-style APIs. 16 17```go 18logger, _ := zap.NewProduction() 19defer logger.Sync() // flushes buffer, if any 20sugar := logger.Sugar() 21sugar.Infow("failed to fetch URL", 22 // Structured context as loosely typed key-value pairs. 23 "url", url, 24 "attempt", 3, 25 "backoff", time.Second, 26) 27sugar.Infof("Failed to fetch URL: %s", url) 28``` 29 30When performance and type safety are critical, use the `Logger`. It's even 31faster than the `SugaredLogger` and allocates far less, but it only supports 32structured logging. 33 34```go 35logger, _ := zap.NewProduction() 36defer logger.Sync() 37logger.Info("failed to fetch URL", 38 // Structured context as strongly typed Field values. 39 zap.String("url", url), 40 zap.Int("attempt", 3), 41 zap.Duration("backoff", time.Second), 42) 43``` 44 45See the [documentation][doc] and [FAQ](FAQ.md) for more details. 46 47## Performance 48 49For applications that log in the hot path, reflection-based serialization and 50string formatting are prohibitively expensive — they're CPU-intensive 51and make many small allocations. Put differently, using `encoding/json` and 52`fmt.Fprintf` to log tons of `interface{}`s makes your application slow. 53 54Zap takes a different approach. It includes a reflection-free, zero-allocation 55JSON encoder, and the base `Logger` strives to avoid serialization overhead 56and allocations wherever possible. By building the high-level `SugaredLogger` 57on that foundation, zap lets users *choose* when they need to count every 58allocation and when they'd prefer a more familiar, loosely typed API. 59 60As measured by its own [benchmarking suite][], not only is zap more performant 61than comparable structured logging packages — it's also faster than the 62standard library. Like all benchmarks, take these with a grain of salt.<sup 63id="anchor-versions">[1](#footnote-versions)</sup> 64 65Log a message and 10 fields: 66 67| Package | Time | Time % to zap | Objects Allocated | 68| :------ | :--: | :-----------: | :---------------: | 69| :zap: zap | 862 ns/op | +0% | 5 allocs/op 70| :zap: zap (sugared) | 1250 ns/op | +45% | 11 allocs/op 71| zerolog | 4021 ns/op | +366% | 76 allocs/op 72| go-kit | 4542 ns/op | +427% | 105 allocs/op 73| apex/log | 26785 ns/op | +3007% | 115 allocs/op 74| logrus | 29501 ns/op | +3322% | 125 allocs/op 75| log15 | 29906 ns/op | +3369% | 122 allocs/op 76 77Log a message with a logger that already has 10 fields of context: 78 79| Package | Time | Time % to zap | Objects Allocated | 80| :------ | :--: | :-----------: | :---------------: | 81| :zap: zap | 126 ns/op | +0% | 0 allocs/op 82| :zap: zap (sugared) | 187 ns/op | +48% | 2 allocs/op 83| zerolog | 88 ns/op | -30% | 0 allocs/op 84| go-kit | 5087 ns/op | +3937% | 103 allocs/op 85| log15 | 18548 ns/op | +14621% | 73 allocs/op 86| apex/log | 26012 ns/op | +20544% | 104 allocs/op 87| logrus | 27236 ns/op | +21516% | 113 allocs/op 88 89Log a static string, without any context or `printf`-style templating: 90 91| Package | Time | Time % to zap | Objects Allocated | 92| :------ | :--: | :-----------: | :---------------: | 93| :zap: zap | 118 ns/op | +0% | 0 allocs/op 94| :zap: zap (sugared) | 191 ns/op | +62% | 2 allocs/op 95| zerolog | 93 ns/op | -21% | 0 allocs/op 96| go-kit | 280 ns/op | +137% | 11 allocs/op 97| standard library | 499 ns/op | +323% | 2 allocs/op 98| apex/log | 1990 ns/op | +1586% | 10 allocs/op 99| logrus | 3129 ns/op | +2552% | 24 allocs/op 100| log15 | 3887 ns/op | +3194% | 23 allocs/op 101 102## Development Status: Stable 103 104All APIs are finalized, and no breaking changes will be made in the 1.x series 105of releases. Users of semver-aware dependency management systems should pin 106zap to `^1`. 107 108## Contributing 109 110We encourage and support an active, healthy community of contributors — 111including you! Details are in the [contribution guide](CONTRIBUTING.md) and 112the [code of conduct](CODE_OF_CONDUCT.md). The zap maintainers keep an eye on 113issues and pull requests, but you can also report any negative conduct to 114oss-conduct@uber.com. That email list is a private, safe space; even the zap 115maintainers don't have access, so don't hesitate to hold us to a high 116standard. 117 118<hr> 119 120Released under the [MIT License](LICENSE.txt). 121 122<sup id="footnote-versions">1</sup> In particular, keep in mind that we may be 123benchmarking against slightly older versions of other packages. Versions are 124pinned in the [benchmarks/go.mod][] file. [↩](#anchor-versions) 125 126[doc-img]: https://godoc.org/go.uber.org/zap?status.svg 127[doc]: https://godoc.org/go.uber.org/zap 128[ci-img]: https://travis-ci.com/uber-go/zap.svg?branch=master 129[ci]: https://travis-ci.com/uber-go/zap 130[cov-img]: https://codecov.io/gh/uber-go/zap/branch/master/graph/badge.svg 131[cov]: https://codecov.io/gh/uber-go/zap 132[benchmarking suite]: https://github.com/uber-go/zap/tree/master/benchmarks 133[benchmarks/go.mod]: https://github.com/uber-go/zap/blob/master/benchmarks/go.mod 134 135