# :zap: zap [![GoDoc][doc-img]][doc] [![Build Status][ci-img]][ci] [![Coverage Status][cov-img]][cov] Blazing fast, structured, leveled logging in Go. ## 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. ```go 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. ```go 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][doc] and [FAQ](FAQ.md) 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.<sup id="anchor-versions">[1](#footnote-versions)</sup> Log a message and 10 fields: | Package | Time | Objects Allocated | | :--- | :---: | :---: | | :zap: zap | 3131 ns/op | 5 allocs/op | | :zap: zap (sugared) | 4173 ns/op | 21 allocs/op | | zerolog | 16154 ns/op | 90 allocs/op | | lion | 16341 ns/op | 111 allocs/op | | go-kit | 17049 ns/op | 126 allocs/op | | logrus | 23662 ns/op | 142 allocs/op | | log15 | 36351 ns/op | 149 allocs/op | | apex/log | 42530 ns/op | 126 allocs/op | Log a message with a logger that already has 10 fields of context: | Package | Time | Objects Allocated | | :--- | :---: | :---: | | :zap: zap | 380 ns/op | 0 allocs/op | | :zap: zap (sugared) | 564 ns/op | 2 allocs/op | | zerolog | 321 ns/op | 0 allocs/op | | lion | 7092 ns/op | 39 allocs/op | | go-kit | 20226 ns/op | 115 allocs/op | | logrus | 22312 ns/op | 130 allocs/op | | log15 | 28788 ns/op | 79 allocs/op | | apex/log | 42063 ns/op | 115 allocs/op | Log a static string, without any context or `printf`-style templating: | Package | Time | Objects Allocated | | :--- | :---: | :---: | | :zap: zap | 361 ns/op | 0 allocs/op | | :zap: zap (sugared) | 534 ns/op | 2 allocs/op | | zerolog | 323 ns/op | 0 allocs/op | | standard library | 575 ns/op | 2 allocs/op | | go-kit | 922 ns/op | 13 allocs/op | | lion | 1413 ns/op | 10 allocs/op | | logrus | 2291 ns/op | 27 allocs/op | | apex/log | 3690 ns/op | 11 allocs/op | | log15 | 5954 ns/op | 26 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](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. <hr> Released under the [MIT License](LICENSE.txt). <sup id="footnote-versions">1</sup> 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. [↩](#anchor-versions) [doc-img]: https://godoc.org/go.uber.org/zap?status.svg [doc]: https://godoc.org/go.uber.org/zap [ci-img]: https://travis-ci.org/uber-go/zap.svg?branch=master [ci]: https://travis-ci.org/uber-go/zap [cov-img]: https://codecov.io/gh/uber-go/zap/branch/master/graph/badge.svg [cov]: https://codecov.io/gh/uber-go/zap [benchmarking suite]: https://github.com/uber-go/zap/tree/master/benchmarks [glide.lock]: https://github.com/uber-go/zap/blob/master/glide.lock